Our list randomization experiment indicates near universal bednet use by the adult population of eastern Gambia, in the year following an LLIN distribution campaign. Though, for feasibility reasons, we did not carry out a direct estimation to assess the validity of our results as some other studies have done (19), the high figures suggest high LLIN usage, at least during the period in which the study took place (towards the end of the transmission season, when coverage is likely to be highest). In fact, the near 100% coverage found in this study was significantly higher than previous studies (16). For example, net coverage in 2010 in the Upper River Region was only 68% (20)..
This study showed very high LLIN use among rural Gambian adults, using a low bias method, in the year following nationwide distribution. Irrespective of the potential limitations in our implementation of the list randomization method, the finding of high LLIN usage is plausible given that the study took place at the end of the high transmission season(21), the study was part of a clinical trial setting (with the associated behavioural effects) and the NMCP had embarked on a net distribution campaign one month earlier.
High usage in a context of high coverage is good news for public health practitioners worried about disuse and misuse, and is consistent with previous research showing high LLIN use even when not purchased (22–24). Net distribution campaigns should take into account these results when estimating effectiveness and planning time between interventions. List randomization may be a useful tool for malaria control programs, but at the same time more research should be carried out on this promising method's robustness, susceptibility to context, and applicability to the specific area of bednet usage.
Our results suggest that virtually all adults in our study area slept under LLIN. Though this may be true, four factors lead us to question the reliability of our results: (1) the estimate of usage is extremely high, even for an area with universal coverage, (2) we lacked any reliable method for validating responses (i.e., direct observation), (3) our study took place in an area where a great deal of health research had already taken place, opening the door to the possibility that our population was not representative of The Gambia as a whole (especially since they had already been sensitized to malaria-related issues given their participation in the housing improvement trial), and (4) the nature of our responses (no minimum or maximum item responses) suggests that there may have been some social desirability bias despite the method. We conclude that our data are indicative of high bednet usage, but more detailed study of the list randomization method in the context of LLIN use is needed, particularly a means of questionnaire-item optimization (to avoid the issue of insufficient response heterogeneity experienced in this study) and external validation (to reliably compare list responses with an objective, observable outcome).
Importantly, among our 196 participants, none stated that they did the minimum (zero) or maximum (four or five, depending on the group) number of activities from our list. There are two possible explanations for this finding. First, it is possible that our list items were poorly chosen and did not provoke sufficient heterogeneity in responses. Second, the list randomization method, though meant to anonymize item-specific responses, may not work in certain contexts. We believe that the second explanation is more likely. The study was carried out in an area where a great deal of health research had been carried out previously, and the field worker was known to be an employee of a health research facility. One potential explanation is that some study participants may have inflated the number of affirmative responses to reduce suspicion by the fieldworker that they were sleeping without a mosquito net. In other words, social desirability bias may have occurred in our study, despite our best efforts to avoid it. Further implementation research is required on both (1) the correct selection of list items, and (2) how the context (who the fieldworker is, etc.) may affect results.
Our approach mirrors that of a recent analysis of sexual behaviours (19) and intimate partner violence (13). However, there are number of limitations to this study. Firstly, it was carried out in an area where considerable research has taken place, and therefore may not be generalizable to the population at large, particularly areas with less research activity. The Medical Research Council Unit in The Gambia have been active in the study area for many years, which might affect knowledge and practices around LLINs, as well as social desirability bias. Our fidelity test between whether children were reported to sleep under a bednet and whether an adult reported (via list randomization) to do the same lacks obvious comparability due to the likely differences in behaviour by age and relatively low number of households where children’s status could be identified. Additionally, we could not validate the reliability of either method (self-reporting or list randomization) through direct observation, due to privacy concerns. Though a movement logger could theoretically be used as a validation tool, the awareness of the logger itself might also bias results, since one can assume that an individual is more likely to use an LLIN if they know their use is being directly monitored. Finally, though our sample size was sufficient for an overall assessment of bednet coverage based on a two-group comparison, we did not have sufficient statistical power to identify the potential determinants of bednet use, such as gender, ethnicity, age, or socioeconomic status. Nonetheless the list randomization test offers a promising new method for exploring LLIN use in study communities.
Our list randomization experiment indicates near universal bednet use by the adult population of eastern Gambia, in the year following an LLIN distribution campaign. Though, for feasibility reasons, we did not carry out a direct estimation to assess the validity of our results as some other studies have done (19), the high figures suggest high LLIN usage, at least during the period in which the study took place (towards the end of the transmission season, when coverage is likely to be highest). In fact, the near 100% coverage found in this study was significantly higher than previous studies (16). For example, net coverage in 2010 in the Upper River Region was only 68% (20)..
This study showed very high LLIN use among rural Gambian adults, using a low bias method, in the year following nationwide distribution. Irrespective of the potential limitations in our implementation of the list randomization method, the finding of high LLIN usage is plausible given that the study took place at the end of the high transmission season(21), the study was part of a clinical trial setting (with the associated behavioural effects) and the NMCP had embarked on a net distribution campaign one month earlier.
High usage in a context of high coverage is good news for public health practitioners worried about disuse and misuse, and is consistent with previous research showing high LLIN use even when not purchased (22–24). Net distribution campaigns should take into account these results when estimating effectiveness and planning time between interventions. List randomization may be a useful tool for malaria control programs, but at the same time more research should be carried out on this promising method's robustness, susceptibility to context, and applicability to the specific area of bednet usage.
Our results suggest that virtually all adults in our study area slept under LLIN. Though this may be true, four factors lead us to question the reliability of our results: (1) the estimate of usage is extremely high, even for an area with universal coverage, (2) we lacked any reliable method for validating responses (i.e., direct observation), (3) our study took place in an area where a great deal of health research had already taken place, opening the door to the possibility that our population was not representative of The Gambia as a whole (especially since they had already been sensitized to malaria-related issues given their participation in the housing improvement trial), and (4) the nature of our responses (no minimum or maximum item responses) suggests that there may have been some social desirability bias despite the method. We conclude that our data are indicative of high bednet usage, but more detailed study of the list randomization method in the context of LLIN use is needed, particularly a means of questionnaire-item optimization (to avoid the issue of insufficient response heterogeneity experienced in this study) and external validation (to reliably compare list responses with an objective, observable outcome).
Importantly, among our 196 participants, none stated that they did the minimum (zero) or maximum (four or five, depending on the group) number of activities from our list. There are two possible explanations for this finding. First, it is possible that our list items were poorly chosen and did not provoke sufficient heterogeneity in responses. Second, the list randomization method, though meant to anonymize item-specific responses, may not work in certain contexts. We believe that the second explanation is more likely. The study was carried out in an area where a great deal of health research had been carried out previously, and the field worker was known to be an employee of a health research facility. One potential explanation is that some study participants may have inflated the number of affirmative responses to reduce suspicion by the fieldworker that they were sleeping without a mosquito net. In other words, social desirability bias may have occurred in our study, despite our best efforts to avoid it. Further implementation research is required on both (1) the correct selection of list items, and (2) how the context (who the fieldworker is, etc.) may affect results.
Our approach mirrors that of a recent analysis of sexual behaviours (19) and intimate partner violence (13). However, there are number of limitations to this study. Firstly, it was carried out in an area where considerable research has taken place, and therefore may not be generalizable to the population at large, particularly areas with less research activity. The Medical Research Council Unit in The Gambia have been active in the study area for many years, which might affect knowledge and practices around LLINs, as well as social desirability bias. Our fidelity test between whether children were reported to sleep under a bednet and whether an adult reported (via list randomization) to do the same lacks obvious comparability due to the likely differences in behaviour by age and relatively low number of households where children’s status could be identified. Additionally, we could not validate the reliability of either method (self-reporting or list randomization) through direct observation, due to privacy concerns. Though a movement logger could theoretically be used as a validation tool, the awareness of the logger itself might also bias results, since one can assume that an individual is more likely to use an LLIN if they know their use is being directly monitored. Finally, though our sample size was sufficient for an overall assessment of bednet coverage based on a two-group comparison, we did not have sufficient statistical power to identify the potential determinants of bednet use, such as gender, ethnicity, age, or socioeconomic status. Nonetheless the list randomization test offers a promising new method for exploring LLIN use in study communities.