Health state preferences are equivalent in the United States and Trinidad and Tobago

Leaders and health administrators in developing countries are interested in using HRQoL instruments from developed countries for a variety of reasons. First, using instruments that are already evaluated and recognized saves the effort of developing them from scratch. Furthermore, developing countries are less likely to possess the expertise and resources to construct and evaluate an instrument. Second, existing instruments produce results in terms and measures already recognized in the field [4]. However, the preferences of HRQoL instruments are based on valuations in the populations from their countries of origin. It is important to determine if the instruments are appropriate for each application [5, 8, 9]. The original QWB preference weights were derived from a probability sample of the non-institutionalized population of San Diego, California [2]. In addition to the general population of San Diego, the instrument has shown evidence of validity in other populations [9, 10]. Because the population of Trinidad was not included in the generation of these weights, it is important to elicit preferences in Trinidad before application of the measure [5, 8].

Although only 50% of the eligible respondents provided ratings, we speculated that the valuations and resulting preferences would remain the same even if all of the eligible respondents had provided ratings. Those who provided ratings did not differ on any of the demographic variables or QWB scores from those who did (Table 1). Since we did not have the direct valuations from the San Diego sample, we calculated weights and compared them with the San Diego US weights. Balaban et al. [9] used the same technique (for the same reason) when they compared patients with arthritis with the sample of the US general population. Overall, we found the US and Trinidad and Tobago weights were highly similar and that the choice of weights would lead to the same conclusions for most analyses.

Our method of eliciting valuations was similar, but not identical to the methods used previously. The QWB was updated during the intervening period from the version used by Patrick et al. [11] and the version used by Balaban et al. [9]. The most recent version is also different from the version used by Balaban et al. [9]. Specifically, the mobility scale has been condensed to three steps from five and the physical activity scale was condensed to three steps from four. This study compared the weights from the most recent version. The method of presenting the scenario was also different. The previous valuation studies had each “scenario” on a single card that the respondent sorted into slots [11]. Thus, the respondents did not have the opportunity to review previous scenarios. In this study, nine vignettes were listed on pages of a booklet. The respondent had the opportunity to review vignettes they previously rated and calibrate the current rating to their previous ratings. While no one changed an earlier rating, a few referred back to prior ratings while rating a vignette. For example, a respondent noted, “I rated vignette 12 with a 7. I think a person in the condition of vignette 20 is worse off. So I will give it 5.” This method of comparison did not appear to materially affect the preferences. There were other differences in calculating preference weights between this study and previous work. The CPX items were maintained in the order of the US standard CPX table, but assigned the Trinidad weights. We averaged the Trinidad weights of two adjacent CPX items for the unrated items. This is in contrast to the standard approach where the average of all CPX weights is assigned to four CPX items that are “not on the respondent’s card” in the United States. Because the most undesirable CPX score is used in calculating the QWB score, the standard approach pulls the QWB score toward the mean when any of the four unrated items end up being the most undesirable CPX. In either case, assigning the average of all CPX weight or the average of two adjacent items is unlikely to have much effect on the average QWB score for the sample. While preference weights for the mobility and physical activity scales had the same ordering with the US and Trinidad preferences, the social activity scale had a slightly different ordering. The US preference weights distinguished not performing major role activity and not performing self-care distinct from the three other levels of the scale. In contrast, the Trinidad preferences distinguished limited role performance and not performing as separate groups with the level of self-care (limited versus did perform) not affecting the preference score. Our findings suggest that elicitation methods can tolerate a small amount of modification [8, 9].

In this study and in the study by Balaban et al. [9], the QWB scores with the study weights were plotted against QWB scores with the original QWB weights. In both studies, the R-square was very high. It reached 0.99 for Balaban et al. [9] and 0.98 in this study. The similarity in the US and Trinidad weights was further evidenced by the similarity in associations of QWB scores with gender, income, education level, and religious affiliation.

Not all studies show these similarities in weights and the differences that have been reported have important policy implications. Johnson et al. [8] reported that valuations for the EQ-5D were different for the United States and the United Kingdom. This research has led some observers to suggest that preference weights might be culture specific [12, 13]. Johnson et al. [8] used virtually the identical time trade-off (TTO) method to elicit valuations in the United States as in the United Kingdom and concluded that the TTO method might have been problematic for several reasons including cultural differences: “… valuations of any health state were elicited in a specific cultural context.” (Johnson et al. [8], p. 227).

Trinidadians are of African descent, Indian descent and Mixtures of the various races that live in close proximity on the island. They write standard English, but speak a peculiar mixture of British English, Spanish, Hindi, French with Sango words and sayings from the Central African Republic. Ethnicity did not have a strong effect on preferences.

Our study further suggests that QWB weights from the US might be appropriate in at least one very different cultural setting. The correspondence between the QWB weights from Trinidad and the QWB weights from the United States in 1975 favors the null hypothesis that health preferences do not migrate as time elapses.

Several limitations were present in this study. First, the probability sample covered three locations rather than the entire country. Therefore, the results pertain to these locations. However, a probability sample is not required to test the validity of the QWB [9, 10]. In addition, the QWB was originally tested on probability sample from San Diego and applied throughout the United States [2]. Second, the large number of interviewers with different levels of medical training added a substantial amount of complexity to a project of this size. The different levels of medical training served to determine the lowest level of medical training needed to successfully administer the QWB in Trinidad. Using clerk-level interviewers could be important for developing Caribbean countries. These workers are well educated and in relatively good supply. They can be used in various healthcare facilities to administer the QWB to patients. The response rate was low due to the length of the interview. The TT-NHIS section covered many aspects of the health care services and took a long time to be completed. The duration ran up against other obligations for some of the respondents. The obligations included things like reacting to rainy weather that frequently causes flooding. In urban areas, flooding paralyzes the city and poses physical threats to adults and children [14]. In rural areas, flooding increases the occurrence of invasion by reptiles that pose threats to children and small animals [15]. Also meals required longer preparation times because ingredients were not usually prepackaged. A meal that included chicken usually began with a live bird. Similarly, fish had to be scaled and cleaned. Thus, parents tended to terminate the interview when mealtimes approached or to secure their home and family during inclement weather. Conducting surveys in developing countries poses challenges not encountered when conducting surveys in developed countries, but the low response rate for preference ratings was not related to health status or demographics and was unlikely to introduce any bias in the preference ratings.

In summary, this study suggests that QWB weights are interchangeable between the United States and Trinidad. In most analyses, weights derived from the Trinidad and Tobago population would produce results similar to those using standard US weights. Leaders and health administrators in other Caribbean countries may use the QWB in their populations with greater confidence that the weights will be appropriate for their populations. While leaders and health administrators can use the QWB with Trinidad weights to assess the impact of disease or injury on the population, for the sake of uniformity and direct comparisons, they might opt to use the US weights.