How to use replicate weights in health survey analysis using the National Nutrition and Physical Activity Survey as an example

Abstract

Objective:To conduct nutrition-related analyses on large-scale health surveys, two aspects of the survey must be incorporated into the analysis: the sampling weights and the sample design; a practice which is not always observed. The present paper compares three analyses: (1) unweighted; (2) weighted but not accounting for the complex sample design; and (3) weighted and accounting for the complex design using replicate weights.Design:Descriptive statistics are computed and a logistic regression investigation of being overweight/obese is conducted using Stata.Setting:Cross-sectional health survey with complex sample design where replicate weights are supplied rather than the variables containing sample design information.Participants:Responding adults from the National Nutrition and Physical Activity Survey (NNPAS) part of the Australian Health Survey (2011–2013).Results:Unweighted analysis produces biased estimates and incorrect estimates of se. Adjusting for the sampling weights gives unbiased estimates but incorrect se estimates. Incorporating both the sampling weights and the sample design results in unbiased estimates and the correct se estimates. This can affect interpretation; for example, the incorrect estimate of the OR for being a current smoker in the unweighted analysis was 1·20 (95 % CI 1·06, 1·37), t= 2·89, P = 0·004, suggesting a statistically significant relationship with being overweight/obese. When the sampling weights and complex sample design are correctly incorporated, the results are no longer statistically significant: OR = 1·06 (95 % CI 0·89, 1·27), t = 0·71, P = 0·480.Conclusions:Correct incorporation of the sampling weights and sample design is crucial for valid inference from survey data.

Consumption of avocado and associations with nutrient, food and anthropometric measures in a representative survey of Australians: a secondary analysis of the 2011–2012 National Nutrition and Physical Activity Survey

“…All statistical analyses were conducted using Stata/IC Version 15 (version 15, StataCorp, 2017). To account for the survey design, sampling process and provide unbiased estimates, replicate weightings were applied using jack-knife resampling in the present analysis (22) . A set of replicate weights and personal weights was supplied with the Confidentialised Unit Record Files.…”

The Profiling of Diet and Physical Activity in Reproductive Age Women and Their Association with Body Mass Index

“…Jack knife replicate weights were used to obtain unbiased standard errors and coefficient estimates. The analysis was based on complete case data, and codes followed recommendations [30] to account for the complex survey design.…”

Nut consumption in a representative survey of Australians: a secondary analysis of the 2011–2012 National Nutrition and Physical Activity Survey

“…Population weights were applied to ensure data were representative of the larger Australian population. Commands were performed in Stata using the complex design model (19) to account for sampling design to calculate means (reported as mean and 95 % CI), median (25th and 75th percentiles) and proportions (reported as a percentage) of interest, as outlined below. Mean and 95 % CI and median and 25th and 75th percentiles for nut consumption (as g/d) were determined for all participants.…”