Introduction
Methods
Study design and participants
Procedures
Questionnaires
Statistical analysis
Measurement property | Statistical methods |
---|---|
Objective 1: Further validity of the MyPOS
| |
Diagonally weighted least squares (DWLS) confirmatory factor analysis using R lavaan package [41] | Goodness-of-fit indices: (a) χ
2/df > 2 [44] (b) Comparative fit index (CFI) of ≥ 0.90 [45] (c) Root mean square error of approximation (RMSEA) of ≤ 0.06, 90% confidence interval 0.05–0.08 [45] (d) Non-normal fit index (NNFI) of ≥ 0.95 or normal fit index (NFI) of ≥ 0.95 [45] Checks of unidimensionality of three separate subscales analysed with Rasch analysis: principal component analysis and paired t-tests in RUMM2030 [46, 47]: (a) RMSEA < 0.08 [48] (b) CFI > 0.90 [49] (c) Tucker-Lewis Index (TLI) > 0.90 [45] |
Floor and ceiling effects via descriptive and Rasch analysis | Data completeness and distribution of item responses >15% of responders at the lower or upper end of the scale [16] Rasch analysis: Scale-to-person targeting, the ability of the scale to cover the whole range of person estimates, shown on the person-item threshold distribution map [29] |
Scaling assumptions via Rasch analysis (RUMM 2030) [42] | |
Fit to the Rasch model | |
Fit of individual items |
Individual item fit Fit residual range −2.5 to +2.5 [50]. The residuals indicate the level of agreement between the observed and expected responses with perfect fit being given if a mean residual is zero with a standard deviation falling between −1 and +1. Positive fit indices above +2.5 show misfit to the model, negative fit indices below −2.5 indicate redundancy of items. Item characteristic curves were examined for graphical item fit |
Person fit |
Person fit Same criteria as item fit |
Reliability |
Reliability: Person Separation Index (measure of internal consistency in Rasch analysis) ≥ 0.70 [51] |
Response options |
Response options: Category probability curve maps for each item examined for disordered answer options, signifying ambiguous labelling or abundance of response options |
Redundant items |
Redundant items Residual correlation matrix, identifying pairs of items with high correlation coefficients (≥0.3) [50] |
Objective 2: Test–retest reliability/item invariance of the MyPOS
| |
Test–retest reliability using Generalizability theory | Restricted maximum-likelihood variance decomposition (VARCOMP) with participants and interaction terms as random factors and items and days as fixed factors. The variance associated with each component of variation, systematic between-person differences in mean item levels, true within-person change over time, idiosyncratic item responses and random measurement error, is partitioned [27, 28]. These variance estimates are used to form indices of the reliability for discriminating between-persons (between-person differences) and within-person change Four generalizability coefficients (all >0.5 [29]): R
1F
Reliability of assessment/screening (Is the MyPOS reliable at each assessment?)
R
1R
Reliability of discrimination (Can the MyPOS reliably distinguish between persons over time?)
R
KF
Test–retest reliability (Is the MyPOS reliable over time?)
R
c
Within-person reliability of change (Can the MyPOS assess change in one person over time?) It should be noted that determination of test–retest reliability within Generalizability theory is a model-based approach that derives reliability indices from variance decomposition as an alternative way to intra-class correlation coefficients. Analysis of test–retest reliability was based on the subgroup of stable patients as indicated by the global rating of change (“unchanged”—see objective 3, responsiveness) |
Item invariance using Rasch analysis | Differential item functioning (DIF) via a two-way ANOVA of standardised residuals with Bonferroni correction for type I error [52]; assessing whether item mean scores showed significant change over all five assessments [50] Significant interaction between class interval (level of quality of life) and time indicates a non-uniform DIF and an unstable, unreliable item |
Objective 3: Responsiveness and minimal important difference (MID(for MyPOS
| |
Responsiveness | GRC to categorise patients into: (a) improved overall QOL (b) deteriorated overall QOL (c) unchanged Differences in mean score changes between each time point and baseline were assessed and graphed. The adequacy of the anchor was assessed via Spearman correlation [17] |
MID: anchor-based approach | Receiver-operating characteristic curve (ROC) to determine optimal cut-off points separately for improvement and deterioration, according to GRC ratings [53]. MID: cut-off point on ROC for which the sum of percentages of false-positive and false-negative classifications [(1-sensitivity or true positive rate) + (1-specificity or false positive rate)] is smallest [39]. Significance of the area under the curve with a p value > 0.5 indicates changes on the MyPOS scores are associated with the gold standard GRC criterion [39]. Graph of distribution of change scores, MIDs and 95% CIs [54] |
MID: distribution-based approach | Standard deviation at baseline used to estimate MID [55] |
Objective 4: acceptability of monitoring
| |
Acceptability | Thematic analysis of responses to open-ended questions about views on self-monitoring and data feedback were analysed using thematic analysis [57] |
Results
Characteristics of patients and questionnaire completion
Variable | |
---|---|
Age, mean ± SD (range) | 68.5 ± 10.5 (range 34–92) |
Men, N (%) | 147 (61.8) |
Married, N(%) | 170 (71.4%) |
White background, N(%) | 220 (92.4%) |
Education level, N(%) | |
Secondary school | 137 (57.5) |
Technical qualification | 52 (21.8) |
University | 41 (17.3) |
Working, N(%) | 41 (17.2) |
Type of myeloma, N(%) | |
IgA or IgG | 180 (78.6) |
Light chain disease | 39 (16.4) |
Other | 9 (3.8) |
ISS stage at diagnosis, N(%) | |
I | 68 (28.6) |
II | 41 (17.2) |
III | 52 (18.6) |
Time since diagnosis (in months), mean (SD) | 39.1 (38.2) |
Disease stage, N(%) | |
Newly diagnosed | 38 (15.9) |
Stable/plateau | 128 (53.8) |
Relapsed/progressive/refractory disease | 72 (30.3) |
Currently receiving treatment, N(%) 118 (49.6) | |
Active therapy | 80 (33.6) |
Maintenance therapy | 38 (15.9) |
Intensity of treatments received, N(%) | |
Chemotherapy only | 111 (46.7) |
Chemotherapy and HSCT | 76 (31.9) |
Two or more HSCT | 15 (6.3) |
Lines of treatment received, mean (SD) | 1.5 (1.2) |
ECOG performance status, N(%) | |
0 Fully active | 79 (33.2) |
1 Restricted | 104 (43.7) |
2 Unable to work | 33 (13.9) |
3 or 4—Limited self-care/bed-bound | 15 (6.3) |
Charlson comorbidity index, mean (SD) | 4.9 (1.5) |
General symptom level (MyPOS), N(%) | |
0 | 3 (1.3) |
1–5 | 70 (29.4) |
6–8 | 65 (72.3) |
9–15 | 92 (38.7) |
Mean number of symptoms, Mean ± SD | 7.4 ± 3.6 |
Total MyPOS, mean ± SD | 26.0 ± 16.8 |
Confirmatory factor analysis of the MyPOS and Rasch scaling
Confirmatory factor analysis
Rasch analysis
Item | Label | Threshold ordering | Item location | Standard error | Item fit residual |
X
2
|
p value | Threshold after collapsing response categories | Item fit residual after reordering |
p value after reordering |
---|---|---|---|---|---|---|---|---|---|---|
Subscale symptoms
| ||||||||||
1 | Pain | √ | −0.48 | 0.08 | −0.01 | 1.5 | 0.674 | – | – | – |
2 | Breathlessness | √ | −0.44 | 0.09 | 0.65 | 4.6 | 0.201 | – | – | – |
3 | Fatigue | √ | −1.16 | 0.09 | −1.28 | 7.2 | 0.067 | – | – | – |
4 | Nausea |
×
| 0.46 | 0.11 | −0.49 | 3.7 | 0.294 | 0/1(A little + moderate)/2(severe + overwhelming) | −0.82 | 0.209 |
5 | Vomiting |
×
| 1.92 | 0.15 | −1.07 | 4.6 | 0.202 | 0/1/2 | −1.76 | 0.028 |
6 | Poor appetite |
×
| 1.52 | 0.09 | −1.34 | 3.2 | 0.357 | 0/1/2 | −1.41 | 0.159 |
7 | Constipation |
×
| −0.37 | 0.08 | −0.43 | 2.5 | 0.472 | 0/1/2 | −0.61 | 0.421 |
8 | Sore or dry mouth | √ | −0.17 | 0.09 | 1.07 | 4.3 | 0.229 | – | – | – |
9 | Drowsiness | √ | −0.27 | 0.09 | −1.13 | 3.7 | 0.290 | – | – | – |
10 | Poor mobility | √ | −0.59 | 0.08 | −1.13 | 6.5 | 0.091 | – | – | – |
11 | Diarrhoea |
×
| 0.22 | 0.10 | 0.89 | 5.5 | 0.138 | 0/1/2 | 0.71 | 0.367 |
12 | Tingling in hands/feet | √ | −0.41 | 0.08 |
2.68
| 16.7 |
0.001
| 0/1/2 | 2.39 | 0.011 |
13 | Difficulty remembering |
×
| −0.21 | 0.09 | 0.25 | 1.5 | 0.687 | 0/1/2 | 0.64 | 0.339 |
Subscale emotional response
| ||||||||||
14 | Anxiety | √ | 0.06 | 0.08 | −2.18 | 15.3 |
0.002
| 0/1/2 | −1.80 | 0.006 |
15 | Family anxiety | √ | −0.26 | 0.07 | 0.87 | 0.7 | 0.864 | 0/1/2 | 0.53 | 0.974 |
16 | Depression |
×
| 0.29 | 0.08 | −0.83 | 7.9 | 0.047 | 0/1/2 | −1.32 | 0.035 |
17 | At peace |
×
| −0.69 | 0.08 | −1.69 | 13.9 |
0.003
| 0/1/2 | −1.20 | 0.036 |
18 | Sharing feelings |
×
| −0.03 | 0.07 |
2.52
| 3.6 | 0.308 | 0/1/2 | 2.49 | 0.041 |
19 | Information |
×
| 0.23 | 0.07 | −0.13 | 2.6 | 0.453 | 0/1/2 | −1.03 | 0.519 |
20 | Practical matters |
×
| 0.31 | 0.08 | 0.45 | 1.3 | 0.741 | 0/1/2 | 0.88 | 0.624 |
21 | Usual activities |
×
| −0.26 | 0.07 | 0.21 | 1.7 | 0.639 | 0/1/2 | −0.21 | 0.705 |
22 | Hobbies |
×
| −0.66 | 0.06 | 0.81 | 8.5 |
0.037
| 0/1/2 | −0.55 | 0.423 |
23 | Quality time with family/friends | √ | 0.26 | 0.08 | −0.91 | 5.7 | 0.126 | 0/1/2 | −1.06 | 0.301 |
24 | Worry about sex life |
×
| 0.17 | 0.08 |
3.16
| 27.6 |
0.001
| 0/1/2 |
2.79
|
0.001
|
25 | Worry about infections |
×
| 0.15 | 0.08 | 1.45 | 4.3 | 0.228 | 0/1/2 | 1.22 | 0.223 |
26 | Worry about physical appearance | √ | 0.29 | 0.08 | −0.17 | 0.3 | 0.953 | 0/1/2 | 0.13 | 0.402 |
27 | Worry about financial situation |
×
| 0.17 | 0.07 | −0.02 | 3.0 | 0.391 | 0/1/2 | 0.44 | 0.285 |
28 | Worry about illness worsening | √ | −0.50 | 0.07 | −1.64 | 8.4 |
0.038
| 0/1/2 | −1.72 | 0.010 |
29 | Coping with illness and treatment |
×
| 0.41 | 0.09 | −1.93 | 19.3 |
0.001
| 0/1/2 | −2.40 | 0.018 |
33 | Information about future |
×
| 0.06 | 0.07 |
2.99
| 19.4 |
0.001
| 0/1/2 |
2.79
| 0.044 |
Subscale: healthcare support
| ||||||||||
30 | Contact for advice |
×
| −0.69 | 0.15 | 0.46 | 1.8 | 0.411 | 0/1/2/3 + 4 | 1.27 | 0.109 |
31 | Knowledge/skill of doctors |
×
| −0.14 | 0.17 | 0.25 | 5.3 | 0.069 | 0/1/2/3 + 4 | 0.56 | 0.023 |
32 | Care and respect |
×
| 0.83 | 0.24 | −0.20 | 4.8 | 0.092 | 0/1/2/3 + 4 | 0.05 | 0.154 |
Floor and ceiling effects
Reliability of the Myeloma Patient Outcome Scale
Source of variance | Total MyPOS | Symptoms | Emotions and functioning | Healthcare support | ||||
---|---|---|---|---|---|---|---|---|
var | % | var | % | var | % | var | % | |
Person | 0.11 | 12.5 | 0.097 | 12.7 | 0.177 | 17.1 | 0.05 | 20.0 |
Time point | 0.143 | 16.2 | 0.164 | 21.4 | 0.108 | 10.4 | 0.005 | 2.0 |
Item | 0.004 | 0.5 | 0.003 | 0.4 | 0.006 | 0.6 | 0.001 | 0.4 |
Person × time point | 0.2 | 22.7 | 0.178 | 23.3 | 0.202 | 19.5 | 0.021 | 8.4 |
Person × item | 0.083 | 9.4 | 0.066 | 8.6 | 0.143 | 13.8 | 0.087 | 34.8 |
Time point × item | 0.007 | 0.8 | 0.006 | 0.8 | 0.009 | 0.9 | 0 | 0.0 |
.Error | 0.334 | 37.9 | 0.251 | 32.8 | 0.393 | 37.9 | 0.086 | 34.4 |
Total | 0.881 | 100.0 | 0.765 | 100.0 | 1.038 | 100.0 | 0.25 | 100.0 |
Standard error of measurement | 6.9 | 3.2 | 4.9 | 1.1 |
Scale | RIF | RIR | RKF | RC | ||||
---|---|---|---|---|---|---|---|---|
Screening | Discrimination | Test–retest reliability* | Reliability of change | |||||
Total MyPOS | 0.553 | 0.233 | 0.970 | 0.642 | ||||
Symptoms subscale | 0.587 | 0.218 | 0.974 | 0.680 | ||||
Emotions subscale | 0.632 | 0.338 | 0.978 | 0.607 | ||||
Healthcare support | 0.734 | 0.591 | 0.986 | 0.423 |
Responsiveness of the Myeloma Patient Outcome Scale
N | Mean changes by GRC | ROC analysis | Effect sizes | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mc
| 95% CI | Cut-off point | Sens/Spec (%) | AUC (95% CI) |
p valueg
| Sum of % misclassified | 95% limit | SDe,f
| Smalla
| Moderateb
| Largec
| ||
Total MyPOSd
| 16.8 | ||||||||||||
Improved | 22/50 | 8.7 | (3.0, 14.3) | 2.5 | 77/66 | 0.717 (0.576, 0.858) |
0.004
| 56.7% | 30.9 | 3.4 | 8.4 | 13.4 | |
Deteriorated | 21/50 | −10.3 | (−17.7, −2.9) | −4.5 | 82/57 | 0.719 (0.568, 0.870) |
0.004
| 60.8% | 18.3 | −3.4 | −8.4 | −13.4 | |
MyPOS symptomd
| 6.1 | ||||||||||||
Improved | 23/64 | 3.3 | (0.8, 5.9) | 1.5 | 65/75 | 0.691 (0.559, 0.823) |
0.007
| 59.8% | 13.5 | 1.2 | 3.1 | 4.9 | |
Deteriorated | 26/64 | −2.7 | (−4.7, −0.7) | −2.5 | 79/57 | 0.687 (0.550, 0.824) |
0.006
| 62.6% | 6.1 | −1.2 | −3.1 | −4.9 | |
MyPOS emotionsd
| 11.3 | ||||||||||||
Improved | 25/59 | 6.1 | (2.8, 9.5) | 4.5 | 56/76 | 0.701 (0.572, 0.830) |
0.004
| 67.7% | 20.2 | 2.3 | 6.2 | 9.0 | |
Deteriorated | 24/59 | −8.0 | (−13.7, −2.3) | −3.5 | 88/54 | 0.691 (0.544, 0.839) |
0.006
| 57.7% | 15.3 | −2.3 | −6.2 | −9.0 | |
MyPOS supportd
| 1.5 | ||||||||||||
Improved | 26/78 | −0.2 | (−1.1, 0.8) | 0.5 | 26/80 | 0.565 (0.442, 0.688) | 0.322 | 92.3% | 3.7 | 0.3 | 0.8 | 1.2 | |
Deteriorated | 29/78 | −0.3 | (−0.8, 0.2) | −0.5 | 78/27 | 0.544 (0.421, 0.667) | 0.481 | 94.2% | 1.8 | −0.3 | −0.8 | −1.2 |