Investigating the suitability of dichotomous responses for the Water Insecurity Experience (WISE) Scales using nationally representative data from 39 countries

Indira Bose , Joshua D Miller , Hilary J Bethancourt, Olga P Garcia , Hugo Melgar-Quiñonez, Rosana Salles-Costa, Mauro E. DelGrossi , Scott Miller, Tessa Durham , Teresa Shamah-Levy, Pablo Gaitán-Rossi , Sera Young, Edward A. Frongillo 

Background 
The Water Insecurity Experiences (WISE) Scales have been validated to comparably measure water insecurity globally. The scales consist of 12 items that can be administered in approximately 3 minutes. There is interest in developing more rapid WISE Scale versions, for use when time is limited. One alternative is to use a subset of 4 items, which has been validated, but has some drawbacks. Here we investigate another alternative: dichotomous (yes/no) response options instead of the original four levels of frequency-based (polytomous) responses. 
Methods/principle findings
We used nationally representative data from 39 countries to simulate dichotomized responses by collapsing the four levels of frequency (never, rarely, sometimes, often/always) into yes/no.  We first explored if “rarely” is meaningful in the gradation of water insecurity, as experiences that occur “rarely” may not be affirmed with dichotomous response options. We tested item-by-item if “rarely” responses predicted dissatisfaction with water quality using logistic regression and found that they were associated with higher odds of dissatisfaction with water quality. As such, some meaningful nuance may be lost if “rare” experiences are not affirmed as “yes”.
We then compared the predictive accuracy of WISE scores using simulated dichotomous responses vs. those calculated using polytomous responses. Based on ROC curves and regression models, dichotomized response scores had good predictive accuracy. Scores calculated using the abbreviated 4-item version were also found to be similarly accurate.
Finally, we explored if it was possible to determine levels of water insecurity that were comparable to the levels calculated using the original responses using dichotomized responses. Using ROC curves, we found that it was possible, which is an advantage over the 4-item scales.
Conclusion/significance
Although polytomous responses options provide more information, dichotomous response options hold promise as a quicker alternative for measuring water insecurity