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Open Access 14-02-2022

The Cyprus Women’s Health Research (COHERE) initiative: normative data from the SF-36v2 questionnaire for reproductive aged women from the Eastern Mediterranean

Auteurs: B. Swift, H. Naci, B. Taneri, C. M. Becker, K. T. Zondervan, N. Rahmioglu

Gepubliceerd in: Quality of Life Research | Uitgave 7/2022

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Abstract

Purpose

Describe the health-related quality of life for a representative cohort of women aged 18–55 in Northern Cyprus.

Methods

We utilised the SF-36-Health-Survey-version-2 (SF-36v2) questionnaire as part of the COHERE Initiative study to calculate the eight physical and mental subscale scores, as well as the two overall summary measures for physical and mental health, where we present results using Cyprus-specific scoring as well as scores based on the test developers’ algorithms. We examined associations between sociodemographic characteristics for both scores.

Results

A total of 7089 women fully completed the SF-36v2 questionnaire (mean age = 36.9), which was reliable and valid in this population. We observed better physical health in ages 18–25 compared to 46–55 (53.32 vs. 46.72 (p < 0.001)) and better mental health in women aged 46–55 compared to 18–25 (52.07 vs. 47.95 (p < 0.001)). Women in employment had better physical and mental health compared to those who were unemployed (physical: 50.25 vs 49.95, p < 0.001 and mental: 50.25 vs 49.24, p = 0.083) and scores increased as educational attainment increased (physical: 47.55 for primary to 51.58 for postgraduate, mental: 48.88 to 50.59, p < 0.001). Turkish Cypriot women had higher scores than Turkish women (physical: 50.42 vs 49.30, mental: 50.43 vs 49.10, p < 0.001).

Conclusion

These are the first population normative values published from a large representative sample of women between 18 and 55 years from the Eastern Mediterranean region. We found better physical health in younger women and better mental health in older women. Turkish Cypriot women and non-migrant women had better mental health, and HRQOL was highest in those in paid employment and those with a higher educational achievement.
Opmerkingen

Supplementary Information

The online version contains supplementary material available at https://​doi.​org/​10.​1007/​s11136-022-03100-7.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Introduction

Health-related quality of life (HRQOL) is important when exploring the general wellbeing of the population, as well to evaluate specific health states. The Short Form-36 Health Survey (SF-36) is a self-reported multi-dimensional measure widely used across countries, with its use ranging from monitoring the burden of disease, to examining the cost-effectiveness of a treatment [1]. In order to aid interpretation of the data, the developers recommend that a normative-based scoring method using US weights is used to provide a standard with which scores from other populations can be compared. However, there is much discussion surrounding whether it is appropriate to use weights that may not be culturally specific, especially when there are differences in health states.
Cyprus is the third largest Mediterranean island with around 300,000 Turkish Cypriot and 700,000 Greek Cypriot residents. There is a lack of population-level health data from Northern Cyprus due to unresolved political circumstances [2, 3] and as a result, this part of the island is absent from any published health statistics from the region. To date, there are no published studies that have provided population normative values in Cyprus for the SF-36, and it is inappropriate to use published values from other countries given the differences in healthcare. A cross-sectional study in Limassol, Republic of Cyprus examined HRQOL in the region [4], but it did not provide normative values for the island and instead used normative values derived from the U.S.A. Another cross-sectional study in Izmir, Turkey, used the SF-36 to provide population norms for the urban population [5]. However, the study took part just after a major economic crisis which is likely to have had an impact on the mental health component of the quality of life scores.
This paper seeks to address the lack of normative data applicable to Northern Cyprus and also serves to add further reference values for the Eastern Mediterranean region. We use data from the Cyprus Women’s Health Research (COHERE) Initiative, to provide population norms for the eight SF-36-Health-Survey version 2 (SF-36v2) health domains as well as the two higher-order summary scores; Physical Component Summary (PCS) and Mental Component Summary (MCS). We examine the reliability and the validity of this dataset and its ability to provide this information, as well as testing the construct validity by investigating statistical relationships between each domain and a range of demographic variables that are known to be related to health outcomes including age, ethnicity, migration status, educational attainment, region of residence, civil status and employment status.

Methods

Study sample: the COHERE Initiative

Normative values for the SF-36v2 and the physical and mental health scoring coefficients were estimated using data collected as part of the COHERE Initiative. The COHERE Initiative is a population based cross-sectional study that has recruited 7646 consenting women between the ages of 18–55 in Northern Cyprus. The aim of COHERE is to determine the relative burden of women’s health conditions and related co-morbidities in women living in Northern Cyprus and as such, establish a women’s health cohort for future follow-up. In short, each participant completed the baseline questionnaire—an expanded version of the Endometriosis-Phenome-and-Biobanking-Harmonization-Project (EPHect) questionnaire [6] which included the SF-36v2 generic health measurement. Data were collected through a combination of household (16%, (n = 1208)) and workplace (84% (6438)) face-to-face visits (93% (7128)) as well as through online (7% (518)) recruitment methods [7], between January 2018 and February 2020. Women aged between 18 and 55 at recruitment, who were either citizens of Northern Cyprus or had been residing there for the past 5 years and were able to give informed consent were eligible to participate in the study. Women were recruited into the study from the 6 main districts in Northern Cyprus (Nicosia, Kyrenia, Famagusta, Morphou, Trikomo and Lefke) with recruitment targets being set using geographic population densities.
We compared the age, educational attainment, civil status, employment status, and city of residence structure of our sample with the projected 2019 population figures for Northern Cyprus obtained from the Northern Cyprus Statistics Institution (available on request from: http://​www.​stat.​gov.​ct.​tr/​). Our sample was broadly representative of these projected values with the main differences being seen in age and education. We calculated weights for age and education and present all SF-36v2 scores obtained from the sample both unweighted and weighted.

Ethics

The study was approved by the Oxford Tropical Research Ethics Committee (OxTREC) of the University of Oxford (OxTREC reference: 37–17). The study also received local ethics approval from the Eastern Mediterranean University Ethics Committee (ETK00-2017-0240).

SF-36v2 health domain subscales

The SF-36 has been validated previously in the Turkish language [8, 9]. Within the SF-36, there are 36 items that measure 8 domains as follows: limitations in physical activity due to health problems (physical functioning, 10 items), limitations in social activities due to physical or emotional problems (social functioning, 2 items), limitations in usual role activities due to physical health problems (role physical, 4 items), limitations in usual role activities due to emotional problems (role emotional, 3 items), wellbeing and psychological distress (mental health, 5 items), energy and fatigue (vitality, 4 items), bodily pain (bodily pain, 2 items) and perceptions of general health (general health, 5 items). Within the 36 items, there is a singular additional question asking about changes in health over the past year. Using the methods set out by Ware et al. [10, 11], the items within each of the above dimensions were coded, summed, and transformed (calculated by subtracting the lowest possible raw score from the actual raw score, dividing by the possible raw score range, and multiplying this by 10. This gave a scale from 0 (worst possible health state as measured by the questionnaire) to 100 (best possible health state).
We also calculated the 8 health domains using norm-based scoring using a T-score transformation where the mean was set to 50 and the standard deviation to 10 in the current sample.

SF-36v2 component summary scores

Following the methods set out in the SF-36v2 manual, the data were factor analysed to produce scoring coefficients for PCS and MCS [11]. In short, we used principal components analysis to produce factor loadings, applied an orthogonal varimax rotation to rotate these loadings and then obtained scores. Calculating PCS involved multiplying each SF-36 scale z-score (calculated by subtracting the mean of SF-36 scale and dividing the difference by the corresponding scale standard deviation) by its respective factor score coefficient and in the case of the MCS, this involved multiplying each SF-36 scale z-score by its respective factor score coefficient. Finally, a T-score transformation was used to standardise the scores whereby the mean was set to 50 and the standard deviation to 10. PCS and MCS are two clusters that are produced from each of the eight scales and allow for further interpretation of the results.
Although no previous studies have investigated the SF-36v2 measures in Northern Cyprus, a cross-cultural adaptation of the survey was shown to be successful in Turkey and demonstrated an acceptable level of reliability and validity in its use in Turkish speaking individuals [5, 8]. To investigate whether the SF-36v2 questionnaire was valid in Northern Cyprus, reliability and validity was assessed. We also calculated summary measures using US-specific health domain subscale scores from 1998 and US-specific factor score coefficients from 1990 [12].

Reliability

Cronbach’s alpha was used to examine internal consistency reliability; a value of > 0.7 was considered satisfactory. To assess whether the summary measures, PCS and MCS were reliable, the reliability of each of the eight subscales, the covariances among them and the factor score coefficients were calculated.

Validity

Principal components analysis, item-subscale correlations (item-rest correlations for the subscales and their respective items) and inter-scale correlations (Spearman correlations) were used to assess construct validity. A value of > 0.4 for item-rest correlations was considered satisfactory. If the correlation between an item and the sum of the other items its respective subscale (item-rest correlation) was shown to be significantly higher than its correlation with other subscales (item-subscale correlations) then the item’s inclusion in its subscale was supported. If the correlation between two subscales was less than their reliability coefficients (Cronbach’s alpha), then it can be said that there is evidence of reliable variance measured by the respective subscales.

Sociodemographic characteristics

We used self-reported data from the COHERE questionnaire in order to obtain potential covariates. Age was calculated by subtracting birthyear from survey completion date and categorised into the following four groups: 18–25, 26–35, 36–45 and 46–55. Ethnicity was split into 3 groups: Turkish Cypriot, Turkish, Mixed/Other (women reporting to have 2 ethnicities and women reporting to be a single ethnicity other than Turkish Cypriot or Turkish). Migration status (born in Northern Cyprus or parents born in Northern Cyprus, not born in Northern Cyprus and therefore recent migrant to the island). Highest educational achievement (primary or middle school, high school or post-secondary, undergraduate and postgraduate), employment status (employed or unemployed), civil status (single, married, divorced/widowed), city of residence (Nicosia, Famagusta, Trikomo, Lefke, Morphou, Kyrenia) were also assessed using the questionnaire data.

Missing data

As we used a large sample size (n = 7646) and the intention of this primary analysis was to obtain the factor loadings to construct the summary scores, data substitution algorithms were not used. In addition to this, there has been speculation that substitution of mean values may have either a conservative or attenuated bias [13]. Given these are the first normative scores to be calculated for women in Northern Cyprus between the ages of 18–55, it is also important to report ‘actual’ scores, so that normative scores here can be used for future analyses and are not differentially attenuated according to the amount of missing data that has been recorded [14]. This approach is consistent with previously published studies [15, 16].

Statistical analyses

Descriptive statistics for each of the eight subscales for the included sample and different subsamples according to age, ethnicity, migration status, educational achievement, civil status, city of residence and employment status were calculated. Differences in means of the eight health subscales for each of the subscales were tested using linear regression. Regressions were computed both crudely and after adjustment for age, as age is usually correlated with the covariates examined here. Regressions for ethnicity and migration status were additionally adjusted for educational achievement and employment classification, as these two demographics are often correlated with non-native people. Statistical analyses were carried out using Stata SE version 16.0.810 (StataCorp LP, College Station, Texas, USA) and R Studio.

Results

Sample population and data completion

Our sample population consists of 7646 women with a mean age of 36.9 years. Women in our cohort were more likely to be Turkish Cypriot (73.8%), native to the island (74.6%) have a university degree (52.7%), be married (66.5%), be in paid employment (81.2%) and reside in the capital city, Nicosia (43.2%) (Table 1). Percentages for whom scale scores could not be calculated due to incomplete items for a particular scale was low and ranged from 0.5 to 2.9% (data not shown).
Table 1
Comparison between various demographics of participants within the Cyprus Women's Health Research (COHERE) Initiative and the census for Northern Cyprus
 
Characteristics
N (%)
COHERE
Census
Age at study (years)
18–25
1108 (14.5)
22,355 (22.7)
26–35
2383 (31.2)
31,228 (31.6)
36–45
2447 (32.0)
25,318 (25.7)
46–55
1708 (22.3)
18,784 (20.0)
Education
Primary or middle school
845 (11.8)
28,426 (33.4)
High school or post-secondary
2557 (35.6)
31,748 (37.3)
Undergraduate
2583 (35.9)
19,713 (23.2)
Postgraduate
1204 (16.8)
5206 (6.1)
Civil status
Single
1753 (24.1)
24,015 (23.8)
Married
4839 (66.5)
68,257 (67.5)
Divorced/separated or widowed
684 (9.4)
8809 (8.7)
Employmenta
In paid employment
5929 (81.2)
46,089 (91.1)
Not in paid work
1374 (18.8)
871 (1.9)
City of residence
Famagusta
1611 (21.1)
25,300 (25.6)
Kyrenia
1263 (16.5)
23,848 (24.2)
Lefke
2691 (3.7)
261 (3.4)
Morphou
585 (7.7)
6095 (6.2)
Nicosia
3301 (43.2)
32,503 (32.9)
Trikomo
625 (8.2)
7249 (7.3)
Only includes women between the ages 18–55. Ethnicity and migration status were not available
aIn paid employment includes both employees and self-employed. Not in paid work includes students, homemakers, retirees, and those without employment

Validation of the SF-36v2 questionnaire for women in Northern Cyprus

Regarding reliability, Cronbach’s alpha coefficients were found to be satisfactory (> 0.70) for all health domains (Table 2), apart from general health (0.69). Reliability of the summary measures was 0.89 for both PCS and MCS.
Table 2
SF-36v2 health domain subscales: mean 0–100 scores with 95% confidence intervals, standard deviation, percentage floor, percentage ceiling, factor score coefficients, and Cronbach's alpha
Scale
N
Mean 0–100 score
95% CI
SD
Percentage floor (%)
Percentage ceiling (%)
Factor score coefficients
Cronbach's alpha
PCS
MCS
Physical functioning (PF)
7607
88.28
(87.92, 88.63)
15.84
0.17
39.49
0.49
− 0.21
0.87
Role Physical (RP)
7558
80.67
(80.15, 81.18)
22.81
0.48
41.81
0.41
− 0.11
0.92
Bodily pain (BP)
7596
68.22
(67.67, 68.77)
24.38
1.20
22.63
0.35
− 0.08
0.87
General health (GH)
7548
63.79
(63.35, 64.24)
19.82
0.21
1.50
0.17
0.08
0.69
Vitality (VT)
7426
57.50
(57.03, 57.97)
20.71
0.83
1.25
− 0.15
0.37
0.74
Social functioning (SF)
7577
77.40
(76.87, 77.92)
23.27
0.73
35.87
0.03
0.22
0.74
Mental health (MH)
7455
64.05
(63.60, 64.50)
19.81
0.31
1.99
− 0.20
0.41
0.83
CI confidence interval, SD standard deviation, PCS physical component summary, MCS mental component summary
When looking at validity, item-rest correlations were all satisfactory apart from PF10 of the physical functioning perception subscale (0.38). The principal components analysis produced two factors with eigenvalue > 1 which indicates a two-factor structure. All items were satisfactory when looking at differences between item-rest correlations and inter-scale correlations i.e. correlations were higher between individual items and their respective subscales, than between individual items and the other 7 subscales. It was also found that the correlations between subscales were lower than their respective Cronbach’s alpha values which suggest that there is unique reliable variance (Table 2). Ceiling effects were highest in physical functioning and role physical subscales (39–42%) with the bodily pain subscale having the highest floor effect (1.20%).

Health domain subscales

Women who were younger had better physical health (PF, RP, BP) compared to older women but as age increased, mean scores for the mental health subscales also increased (VT, RE, MH) (Table 3). Though GH increased with age, this was not statistically significant. When considering ethnicity, women who self-reported to be Turkish had the lowest scores across all domains except MH, RE, SF, and all but PF remained statistically significant after adjustment for age (Table 4). Women who were not migrants had higher subscale scores for all the domains compared to women with a migration background (PF, BP, GH, VT, SF, RE, MH (Supplementary Table 2). After adjustment for age, married women generally had the best mental health (MH, RE, SF) but the worst physical health (PF, RP, BP) (Supplementary Table 3). Residency of the women in COHERE did not appear to significantly affect physical or mental health domains (Supplementary Table 4). As educational attainment increased, mean physical health also increased after adjustment for age, (PF, RP, BP, GH) as did mental health domains (VT, RE and MH) (Table 5). Generally, women who were employed had significantly better physical subscale scores (PF, RP, BP, GH) with only the VT mental health score remaining significant after adjustment for age (Table 6).
Table 3
SF-36v2 health domain subscales: mean 0–100 scores with 95% confidence intervals, standard deviation, p values from linear regression (global test) according to age (18–25, 26–35, 36–45, 46–55)
Scale
18–25 years
26–35 years
36–45 years
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
Physical functioning (PF)
1107
93.23
(92.50, 93.97)
12.46
2374
90.97
(90.42, 91.53)
13.77
2431
87.90
(87.28, 88.52)
15.61
Role Physical (RP)
1103
85.17
(83.94, 86.41)
20.93
2361
82.09
(81.19, 82.99)
22.30
2407
79.50
(78.58, 80.41)
22.84
Bodily pain (BP)
1100
72.07
(70.64, 73.49)
24.08
2370
69.93
(68.98, 70.89)
23.71
2426
67.28
(66.31, 68.25)
24.39
General health (GH)
1098
63.41
(62.22, 64.60)
20.07
2361
64.35
(63.57, 65.13)
19.32
2413
62.87
(62.07, 63.68)
20.18
Vitality (VT)
1086
56.19
(54.95, 57.43)
20.84
2315
57.35
(56.54, 58.17)
20.08
2372
57.18
(56.34, 58.02)
20.86
Social functioning (SF)
1100
77.32
(75.95, 78.68)
23.07
2363
76.78
(75.82, 77.73)
23.74
2420
77.71
(76.80, 78.61)
22.75
Role emotional (RE)
1093
73.73
(72.22, 75.23)
25.33
2333
76.79
(75.82, 77.75)
23.85
2379
77.78
(76.83, 78.72)
23.50
Mental health (MH)
1085
62.09
(60.87, 63.32)
20.57
2339
63.91
(63.13, 64.69)
19.30
2370
63.73
(62.94, 64.53)
19.71
Scale
46–55 years
p value
N
Mean 0–100 score
95% CI
SD
Physical functioning (PF)
1695
81.81
(80.92, 82.69)
18.50
 < 0.001
Role physical (RP)
1687
77.39
(76.25, 78.54)
23.98
 < 0.001
Bodily pain (BP)
1700
64.68
(63.50, 65.87)
24.92
 < 0.001
General health (GH)
1676
64.58
(63.63, 65.53)
19.76
0.665
Vitality (VT)
1653
59.03
(58.01, 60.05)
21.21
0.001
Social functioning (SF)
1694
77.88
(76.76, 79.00)
23.47
0.146
Role emotional (RE)
1652
78.80
(77.68, 79.93)
23.25
 < 0.001
Mental health (MH)
1661
65.99
(65.03, 66.95)
19.98
 < 0.001
N total number CI confidence interval, SD standard deviation
p values from linear regression (crude)
p values < 0.05 are bold
Table 4
SF-36v2 health domain subscales: mean 0–100 scores with 95% confidence intervals, standard deviation, p values from linear regression (global test) without and with adjustment for age according to ethnicity (Turkish Cypriot, Turkish, Other/Mixed)
Scale
Turkish Cypriot
Turkish
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
Physical functioning (PF)
5359
88.71
(88.30, 89.13)
15.52
1516
87.30
(86.45, 88.15)
16.91
Role physical (RP)
5323
81.26
(80.67, 81.86)
22.23
1507
79.69
(78.46, 80.93)
24.40
Bodily pain (BP)
5346
69.40
(68.76, 70.04)
23.79
1516
64.72
(63.40, 66.03)
26.09
General health (GH)
5317
64.61
(64.08, 65.13)
19.60
1501
61.54
(60.49, 62.59)
20.75
Vitality (VT)
5238
58.53
(57.99, 59.08)
20.21
1472
54.38
(53.26, 55.51)
22.04
Social functioning (SF)
5335
78.13
(77.53, 78.74)
22.58
1512
76.58
(75.33, 77.83)
24.77
Role emotional (RE)
5260
77.94
(77.32, 78.57)
23.22
1480
75.72
(74.42, 77.02)
25.45
Mental health (MH)
5261
64.86
(64.34, 65.38)
19.22
1481
62.29
(61.22, 63.37)
21.14
Scale
Other/mixed
p value
N
Mean 0–100 score
95% CI
SD
Crude
Adjusted for age
Physical functioning (PF)
383
89.92
(88.66, 91.19)
12.63
0.362
0.116
Role physical (RP)
384
80.32
(78.03, 82.62)
22.96
0.042
0.020
Bodily pain (BP)
384
67.21
(64.72, 69.69)
24.85
 < 0.001
 < 0.001
General health (GH)
386
63.85
(61.95, 65.75)
19.04
 < 0.001
 < 0.001
Vitality (VT)
381
55.61
(53.40, 57.82)
22.01
 < 0.001
 < 0.001
Social functioning (SF)
386
73.45
(70.87, 76.02)
25.83
 < 0.001
 < 0.001
Role emotional (RE)
379
74.85
(72.38,77.31)
24.51
 < 0.001
 < 0.001
Mental health (MH)
379
61.46
(59.24, 63.69)
22.13
 < 0.001
 < 0.001
N total number CI confidence interval, SD standard deviation
p values from linear regression (crude) and with adjustment for age (adjusted for age)
p values < 0.05 are bold
Table 5
SF-36v2 health domain subscales: mean 0–100 scores with 95% confidence intervals, standard deviation, p values from linear regression (global test) without and with adjustment for age according to educational attainment (Primary or middle school, high school or post-secondary, undergraduate degree, postgraduate degree)
Scale
Primary or middle school
High school or post-secondary
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
Physical functioning (PF)
838
84.18
(82.87, 85.48)
19.29
2538
87.23
(86.59, 87.87)
16.53
Role physical (RP)
834
77.63
(75.80, 79.46)
26.97
2516
80.00
(79.09, 80.91)
23.34
Bodily pain (BP)
843
61.37
(59.47, 63.28)
28.24
2537
67.43
(66.46, 68.40)
24.87
General health (GH)
831
58.42
(56.96, 59.88)
21.44
2516
63.45
(62.65, 64.26)
20.67
Vitality (VT)
820
51.27
(49.69, 52.84)
23.01
2467
57.14
(56.27, 58.01)
22.03
Social functioning (SF)
842
76.68
(74.92, 78.44)
26.03
2526
77.39
(76.47, 78.31)
23.55
Role emotional (RE)
816
77.15
(75.37, 78.94)
26.00
2478
76.70
(75.75, 77.65)
24.14
Mental health (MH)
821
61.19
(59.64, 62.73)
22.58
2486
63.44
(62.62, 64.25)
20.70
Scale
Undergraduate degree
Postgraduate degree
p value
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
Crude
Adjusted for age
Physical functioning (PF)
2579
90.27
(89.75, 90.79)
13.56
1203
90.54
(89.74, 91.34)
14.12
 < 0.001
 < 0.001
Role physical (RP)
2570
81.96
(81.15, 82.77)
20.99
1197
82.84
(81.63, 84.05)
21.36
 < 0.001
 < 0.001
Bodily pain (BP)
2570
69.94
(69.06, 70.83)
22.95
1196
71.55
(70.27, 72.82)
22.44
 < 0.001
 < 0.001
General health (GH)
2566
64.86
(64.14, 65.58)
18.63
1193
66.79
(65.72, 67.85)
18.76
 < 0.001
 < 0.001
Vitality (VT)
2525
58.85
(58.09, 59.60)
19.32
1183
59.95
(58.89, 61.00)
18.49
 < 0.001
 < 0.001
Social functioning (SF)
2566
77.84
(76.97, 78.71)
22.38
1198
78.01
(76.74, 79.27)
22.37
0.162
0.094
Role emotional (RE)
2540
77.54
(76.65, 78.44)
23.07
1189
78.30
(77.02, 79.58)
22.58
0.095
0.012
Mental health (MH)
2535
65.02
(64.30, 65.74)
18.46
1182
65.79
(64.75, 66.83)
18.22
 < 0.001
 < 0.001
N total number CI confidence interval, SD standard deviation
p values from linear regression (crude) and with adjustment for age (adjusted for age)
p values < 0.05 are bold
Table 6
SF-36v2 health domain subscales: mean 0–100 scores with 95% confidence intervals, standard deviation, p values from linear regression (global test) without and with adjustment for age according to employment status (In paid employment, not in paid employment)
Scale
In paid employment
Not in paid employment
p value
N
Mean 0–100 score
95% CI
SD
N
Mean 0–100 score
95% CI
SD
Crude
Adjusted for age
Physical functioning (PF)
5901
88.49
(88.10, 88.88)
15.26
1370
88.28
(87.36, 89.21)
17.50
0.659
 < 0.001
Role physical (RP)
5865
80.97
(80.40, 81.53)
21.98
1362
80.51
(79.15, 81.87)
25.67
0.506
0.029
Bodily pain (BP)
5890
68.56
(67.96, 69.17)
23.62
1368
67.33
(65.87, 68.80)
27.58
0.093
0.003
General health (GH)
5860
64.58
(64.09, 65.08)
19.34
1357
61.12
(59.97, 62.28)
21.63
 < 0.001
 < 0.001
Vitality (VT)
5762
58.19
(57.67, 58.72)
20.21
1343
54.79
(53.57, 56.01)
22.81
 < 0.001
 < 0.001
Social functioning (SF)
5878
77.33
(76.74, 77.92)
23.05
1367
78.45
(77.17, 79.72)
24.09
0.110
0.066
Role emotional (RE)
5780
77.64
(77.04, 78.24)
23.25
1351
75.98
(74.60, 77.36)
25.84
0.021
0.127
Mental health (MH)
5781
64.32
(63.82, 64.82)
19.40
1352
63.44
(62.29, 64.59)
21.54
0.143
0.430
In paid employment includes both employees and self-employed. Not in paid work includes students, homemakers, retirees, and those without employment
N total number CI confidence interval, SD standard deviation
p values from linear regression (crude) and with adjustment for age (adjusted for age)
p values < 0.05 are bold
The 8 domains presented as norm-based scores can be seen in the Appendix (Supplementary Tables S4-S10).

SF-36v2 summary measures PCS and MCS

Principal components analysis and orthogonal rotation was used to factor analyse the data and led to a two-factor solution; factor labelled PCS gained an eigenvalue of 4.00, with MCS having an eigenvalue of 1.14. We found better physical health (PCS) in younger women and generally better mental health in older women (Table 7). Higher scores were seen in women with a higher educational achievement and those in paid employment. Single women appeared to have the best physical health and the worst mental health (mean age in single women = 27.03 (SD 7.20) vs married women = 39.74 (SD 8.16)). Women residing in Morphou had the lowest PCS scores and those in Famagusta the worst MCS scores, with women in Kyrenia having the highest PCS scores and those in Lefke the highest MCS scores. These associations were not significant once adjusting for age (mean age and SD in each district as follows: Famagusta (mean = 35.5 (SD 9.8)), Kyrenia (mean = 37.2 (SD 9.4)), Lefke (mean = 38.1 (SD 9.5)), Morphou (mean = 37.6 (SD 10.2)), Nicosia (mean = 37.4 (SD 9.3)) and Trikomo (mean = 36.1 (SD 10.3)) (Table 7). Turkish Cypriot women had both the best physical (with other/mixed ethnicities) and mental health scores after adjustment for age as did those women with a non-migration background. After further adjustment for education and occupation classification, associations were especially attenuated for migration status and health scores and although the effect was also lessened between ethnicity and the two health scores, associations remained significant for  MCS (not shown).
Table 7
PCS, MCS: mean (T-scores) with 95% CI, SD and p values from linear regression (global test) without and with adjustment for age for the overall sample (n = 7089) and subsamples according to age, ethnicity, educational achievement, civil status, city of residence, employment status*
Characteristics
PCS
p value
MCS
p value
Mean T-score
95% CI
SD
Crude
Adjusted for age
Mean T score
95% CI
SD
Crude
Adjusted for age
Overall sample
50.10
(49.87, 50.34)
9.97
50.01
(49.78, 50.25)
10.01
Age
   
 <0.001
    
 <0.001
 
 18–25
53.32
(52.82, 53.83)
8.34
 
47.95
(47.31, 48.59)
10.50
 
 26–35
51.50
(51.12, 51.87)
9.10
  
49.43
(49.02, 49.84)
9.97
  
 36–45
49.58
(48.17, 50.00)
10.01
  
50.13
(49.72, 50.53)
9.86
  
 46–55
46.72
(46.18, 47.26)
10.96
  
52.07
(51.59, 52.54)
9.56
  
Ethnicity
   
 0.072
 0.014
   
 <0.001
 <0.001
 Turkish Cypriot
50.42
(50.15, 50.69)
9.76
  
50.43
(50.16, 50.70)
9.76
  
 Turkish
49.30
(48.74, 49.86)
10.71
  
49.10
(48.55, 49.66)
10.59
  
 Other/mixed
50.82
(49.88, 51.76)
9.05
  
48.40
(47.26, 49.55)
11.06
  
Educational achievement
   
 < 0.001
 < 0.001
   
 < 0.001
 < 0.001
 Primary or middle school
47.55
(46.70, 48.40)
12.17
  
48.88
(48.14, 49.63)
10.64
  
 High school or post-secondary
49.60
(49.18, 50.01)
10.26
  
49.95
(49.53, 50.37)
10.42
  
 University
51.04
(50.69, 51.39)
8.84
  
50.24
(49.86, 50.63)
9.57
  
 Postgraduate
51.58
(51.05, 52.11)
9.13
  
50.59
(50.03, 51.14)
9.59
  
Civil status
   
 < 0.001
 < 0.001
   
 < 0.001
0.047
 Single
52.70
(52.28, 53.12)
8.77
  
48.61
(48.10, 49.11)
10.53
  
 Married
49.21
(48.91, 49.51)
10.10
  
50.64
(50.35, 50.92)
9.69
  
 Divorced/separated or widowed
50.68
(49.87, 51.48)
10.41
  
49.80
(48.97, 50.62)
10.65
  
Migration status
   
 < 0.001
0.002
   
 < 0.001
 < 0.001
 Non migration status
50.48
(50.22, 50.75)
9.70
  
50.33
(50.06, 50.61)
9.87
  
 Migration status
49.39
(48.89, 49.90)
10.56
  
49.18
(48.68, 49.68)
10.47
  
City of residence
   
0.019
0.182
   
0.243
0.578
 Famagusta
50.43
(49.93, 50.94)
9.90
  
49.60
(49.08, 50.11)
10.11
  
 Kyrenia
50.62
(50.07, 51.16)
9.59
  
50.04
(49.46, 50.62)
10.12
  
 Lefke
49.86
(48.63, 51.08)
9.68
  
51.37
(50.20, 52.53)
9.19
  
 Morphou
49.14
(48.24, 50.04)
10.83
  
50.20
(49.33, 51.07)
10.48
  
 Nicosia
50.08
(49.74, 50.42)
9.68
  
50.03
(49.68, 50.38)
9.87
  
 Trikomo
49.38
(48.45, 50.31)
11.45
  
50.20
(49.38, 51.02)
10.05
  
Employment statusa
   
0.317
 < 0.001
   
0.001
0.083
 In paid employment
50.25
(50.00, 50.50)
9.50
  
50.25
(49.99, 50.51)
9.87
  
 Not in paid work
49.95
(49.32, 50.58)
11.59
  
49.24
(48.66, 49.82)
10.65
  
PCS Physical Component Summary MCS Mental Component Summary, CI confidence interval SD standard deviation
P values from linear regression (crude) and with adjustment for age (adjusted for age)
P values < 0.05 are bold
aIn paid employment includes both employees and self-employed. Not in paid work includes students, homemakers, retirees, and those without employment
After weighting our data by age and education we did not see great differences in the results (Supplementary Tables S11-S19).
PCS estimates calculated using US coefficients were broadly similar to those generated using our sample; however, we found that the MCS estimates were substantially lower (Supplementary Tables S20-S21).

Discussion

We have shown that the SF-36v2 questionnaire is both reliable and valid in women between the ages of 18–55 residing in Northern Cyprus in evaluating HRQOL. We found better physical health in younger women and better mental health in older women. Turkish Cypriot women and non-migrant women had both better mental and physical health, and HRQOL was highest in those in paid employment as well as in those with a higher educational achievement. Here we have provided the first normative values for women in Northern Cyprus aged between 18 and 55 and our analysis suggests that choosing culturally specific weighting coefficients is important when investigating HRQOL.

Reliability and validity

Internal consistency reliability of the scales was high (above 0.8) for 5 of the eight scales with the general health scale being the only one to fall somewhat short of the accepted Cronbach’s alpha level of 0.7 (0.69). However, we believe this to be sufficiently close to argue that this scale too had adequate internal consistency reliability. The highest ceiling value in our sample was 41.8%, for the role physical scale, suggesting that the SF-36v2 was well interpreted and suited to our population of Northern Cyprus.

Physical and mental health domains

This study has shown that the highest score of the eight health domains for participants in COHERE was physical functioning and the lowest was vitality. This pattern is consistent with various other studies conducted in a number of high-income countries such as the United Kingdom [16], Switzerland [17] and the United States [11], as well as countries within the Mediterranean region such as Turkey [5] and Greece [18]. Although the scores we present here vary from those presented by other countries, this does not necessarily mean that there are international health differences; there are a number of reasons normative scores may differ between countries, such as differences in culture, expectation of health and mode of administration of the questionnaire.
We observed that as age increased, mean physical health decreased and mean mental health increased, as seen in various other studies [11, 16, 17]. Education and employment are two demographics that can be used as proxies for the sociodemographic position of people within society. As our results showed higher mean scores in those who had obtained higher educational qualifications as well as in those who were in paid employment, we can be confident that the SF-36v2 was capable of detecting these known differences amongst different socioeconomic positions.
Compared to migrant women, non-migrants had the highest mean scores after adjustment for age only, consistent with previously published studies [17, 19]. Once education and occupation type had been adjusted for, the associations were no longer statistically significant, suggesting the observed associations may be partly explained by social disadvantages that arose from lower socioeconomic status immigrants in this sample. When examining ethnicity, after adjustment for age, education, and occupation class, the statistically significant association between ethnicity and mental health remained, with Turkish Cypriot women having the highest mean scores. Most studies examining HRQOL in non-natives show that they suffer from higher stressors when compared to their native counterparts, not only due to differences in socioeconomics, but due to other migration-specific difficulties [20, 21].
The area most similar to Northern Cyprus both geographically and culturally to have produced normative values for the SF-36v2 is Turkey [5]. Mean health domain scores in COHERE were lower for all scales, apart from physical functioning (88.3 vs 80.6). The study in Turkey was focussed on an urban region with a small sample size (670 women) which is not representative of the population of Turkey. In addition to this, five of the eight scales had a median ceiling score of 100 (perfect) which is unusually high. We believe this is why normative HRQOL scores should be both country and culturally specific.

Strengths and limitations

The cross-sectional design of our study means that we cannot infer causality of measured variables. Gandek and Ware [22] recommend that the minimum sample size used to produce country specific normative values for HRQOL using the SF-36v2 should be between 2500 and 3000 respondents. Here our large sample size (n = 7646) means we can be confident in the accuracy of our values and in addition to this, the demographic and social background characteristics of participants in our sample are broadly representative of women between the ages of 18–55 in Northern Cyprus. However, there is some over-representation of women with university degrees and in employment compared to the general population and this should be considered when carrying out any further analyses.
Although the SF-36v2 is a self-administered questionnaire and therefore may suffer from reporting bias, it is reliable and valid as well as being a widely used tool to assess HRQOL. Our study is unique in that it provides normative values for a female population. It is well established that HRQOL is significantly lower in women compared to men and therefore using female-specific normative values from a population of premenopausal women is especially advisable when investigating the impact of women’s reproductive diseases, such as endometriosis, on HRQoL. The main aim of the COHERE Initiative is to investigate reproductive health conditions and so our study is restricted to women between the ages of 18–55. Therefore, it is not generalisable to women above and below these ages or to men and so further research in these groups would be needed to discover if similar patterns exist and to provide normative values for all age groups.

Conclusion

Here we present the normative values for women aged 18–55 in Northern Cyprus using the SF-36v2 questionnaire. In accordance with the literature, we saw higher mean physical health scores in younger women and higher mean mental health scores in older women. Non-Turkish Cypriot women and migrants had lower mean scores for both domains, as did those who had lower educational attainments and those who were not in paid employment. This research will allow future studies to measure HRQOL as assessed by the SF-36v2 questionnaire using female-specific data in Northern Cyprus, which we argue is essential in order to investigate the impact women’s health diseases have on HRQOL.

Acknowledgements

We would like to thank all the women who volunteered to take part in our study and our research assistants from Eastern Mediterranean University who conducted the baseline recruitment in the field namely Ecem Fidan, Kamil Ipciler, Asya Koparan, Cise Mis, Elif Okur, Zisan Pekri, Pembe Savas, Melis Tarhan, Ebru Yasti Gokcen Kofali, Gizem Gurpinar, Sumeyye Istanbul, Dilara Altan, and the data entry team. We are grateful to the Cyprus Women’s Health Research Society (CoHERS) civil society members for their support of the project in spreading the world and reaching the women in Northern Cyprus. We would like to also acknowledge the Northern Cyprus Statistics Institution, in particular, Erkan Muhtaroglu and Dr. Turel Ozer Oksuzoglu for sharing the 2019 census projections. We also thank the two anonymous reviewers for their helpful comments that improved our manuscript.

Declarations

Conflict of interest

CMB declares that he is part of a scientific collaboration between Oxford University and Bayer Healthcare Ltd. for the purpose of drug target identification in endometriosis. He holds/has held research grants from Bayer Healthcare, Volition Rx, MDNA Life Sciences and Roche Diagnostics and has in recent years been a consultant for Abbvie Inc. and Roche Diagnostics. KTZ declares that she has scientific collaborations outside the submitted work with Bayer Healthcare, MDNA Life Sciences, Roche Diagnostics Inc., and Volition Rx and is a Board member (Secretary) of the World Endometriosis Society, Research Advisory Board member of Wellbeing of Women, UK (research charity) and Chair of the Research Directions Working Group, World Endometriosis Society. NR declares that she is the founding president of Cyprus Women’s Health Research Society in Northern Cyprus.

Ethical approval

Two ethics approvals were obtained for the study: (1) International ethics approval from the Oxford Tropical Research Ethics Committee (OxTREC) of the University of Oxford (OxTREC reference: 37–17) and (2) Local ethics approval from the Eastern Mediterranean University Ethics Committee (ETK00-2017-0240).
After the participant had been informed about the study and made the decision to take part, a written consent was obtained.
Not applicable.
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Metagegevens
Titel
The Cyprus Women’s Health Research (COHERE) initiative: normative data from the SF-36v2 questionnaire for reproductive aged women from the Eastern Mediterranean
Auteurs
B. Swift
H. Naci
B. Taneri
C. M. Becker
K. T. Zondervan
N. Rahmioglu
Publicatiedatum
14-02-2022
Uitgeverij
Springer International Publishing
Gepubliceerd in
Quality of Life Research / Uitgave 7/2022
Print ISSN: 0962-9343
Elektronisch ISSN: 1573-2649
DOI
https://doi.org/10.1007/s11136-022-03100-7

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