Anemia design effects in cluster surveys of women and young children in refugee settings.

Background Nutrition surveys in many refugee settings routinely estimate anemia prevalence in high-risk population groups. Given the lack of information on anemia design effects (DEFF) observed in surveys in these settings, the goal of this paper is to better understand the magnitude and distribution of DEFFs and intracluster correlation coefficients (ICCs) in order to inform future survey design. Methods Two-stage cluster surveys conducted during 2013-2016 were included if they measured hemoglobin in refugee children aged 6-59 months and/or non-pregnant women aged 15-49 years. Prevalence of anemia, anemia DEFFs and ICCs, mean cluster size, number of clusters, and total sample size were calculated per-survey for non-pregnant women and children. Non-parametric tests were used to assess differences and correlations of ICC and DEFF between women and children and inter-regional differences. Results Eighty-seven unique cluster surveys from nine countries were included in this analysis. More than 90% of all surveys had ICC values for anemia below 0.10. Median ICC for children was 0.032 (IQR: 0.015-0.048), not significantly different from that observed for non-pregnant women for whom the median was 0.024 (IQR: -0.002-0.055). DEFFs were significantly higher for children [1.54 (IQR: 1.21-1.82)] versus women [1.20 (IQR: 0.99-1.46)]. Regional differences in DEFFs and ICCs were observed. Conclusions Both ICCs and DEFF were relatively small for both non-pregnant women and preschool children and fall in a narrow range. Differences in ICCs between women and children were non-significant, suggesting similar inter-cluster distributions of anemia; significant differences in DEFF were likely attributable to differing cluster sizes. Given regional differences in both ICCs and DEFFs, location-specific values are preferred. However, in the absence of other context-specific information, we suggest using DEFFs of 1.4-1.8 if mean cluster size is around 20, and DEFFs of 1.2-1.4 if mean cluster size is around 10.