Therefore, programme managers may act conservatively and have sample sizes higher than required to determine population iodine status. Therefore, it is not valid to calculate or present prevalence of iodine deficiency (which implies a count and comparison of people with adequate and inadequate iodine status).Īccording to the UNICEF 2018 guidance,2 there is uncertainty on the best methods for power calculations to determine population iodine status using spot UIC measurements. Because there is high variability in individual iodine excretion throughout the day, a single urine sample and resulting UIC cannot be considered to reflect an individual’s iodine status. Iodine status is normally assessed in cluster surveys using casual (single sample) urine samples. For example, a median urinary iodine concentration (UIC) of 100-199 µg/L indicates adequate iodine intake among a population of school-age children. Special considerations for calculation of sample size in surveys assessing iodine statusĬurrent recommendations for survey sample collection and data analysis are based on the determination of population - not individual - iodine status. Whatever decisions are made regarding sample size calculations, they should all be documented in the methodology sections of the survey protocol, human subject documents and final survey report. A rationale for acceptable precision and the final proposed size should be agreed for each indicator and population group. The assumptions behind the differences between sample sizes should be discussed with the Steering committee and Technical committee. Module 5 / Calculation of sample size for a single cross-sectional cluster survey Calculation of sample size for a single cross-sectional cluster surveyīecause sample size calculations are based on a number of different decisions and estimates, a range of sample sizes may be produced for a single indicator and population group.
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