The WHO-UNICEF minimum dietary diversity (MDD) indicator for children aged 6–23 months is a global monitoring indicator used to track multi-year population-level changes in dietary quality, but the influence of seasonality on MDD estimates remains unclear.
Examine how seasonality of data collection may influence population-level MDD estimates and inferences about MDD change over multiple survey years.
Three countries were selected with three or more consecutive years of MDD data collection including continuous national Demographic Health Surveys in Senegal (2012–2017, N = 12,183) and Peru (2005–16, N = 35,272) and the PoSHAN sentinel site seasonal surveys (covering 3 seasons/year) in Nepal (2013–2016, N = 1309). MDD prevalence (≥5 of 8 food groups) and an 8-item continuous food group score (FGS) and 95% confidence intervals were estimated by month and compared for lean and non-lean seasons using Ordinary Least Squares (OLS) regression with dummy variables for year.
The national prevalence of MDD was higher in Peru (75.4%) than in Nepal (39.1%) or in Senegal (15.7%). Children in Peru were 1.8% [coefficient: –0.0179 (–0.033, –0.002)] less likely to achieve MDD during the lean season. Similar seasonal magnitudes were observed in Senegal [–0.0347, (–0.058, –0.011)] and for Nepal [–0.0133 (–0.107, 0.081)]. FGS was about 0.1 item lower during the lean season in all three countries. In comparison, MDD increased by an average rate of only 4.2 and 4.4 percentage points per five years in Peru and Senegal respectively. Intake of specific food groups was stable across months in all countries with the provitamin-A rich food group exhibiting the most seasonality.
The magnitude of seasonal variation in MDD prevalence was smaller than expected but large relative to longer term changes. If large-scale surveys are not conducted in the same season, biased conclusions about trends are possible.