Response to 'Effects of parity on lifestyle changes: from a methodological perspective to societal applications'.

Abstract

We appreciate the interest of Anamege and Perez-Carreno in our article titled ‘Assessing patterns of change in lifestyle behaviours by parity: a longitudinal cohort study’.1 We are also grateful to the editor for the opportunity to respond and to provide further details about our work. We excluded all respondents with implausible energy intake (n = 286) from all analyses (these were not part of the 4927 participants included in the final analysis). We only excluded the 573 women who were pregnant in sensitivity analysis to explore the impact of pregnancy including confounding (these were included in the 4927 participants in the final analysis). Missing data on weight and body mass index (BMI) reported in Table 1 of the published manuscript were from the baseline in 2003 (Survey 3).1 At Survey 5 in 2009 (the endpoint in our analysis), missing data for both weight and BMI in parous women was lower, at 1%. Hence previous weight and BMI measurements did not seem to affect women’s willingness to provide data in subsequent surveys. The pattern of missingness in weight and BMI data is consistent with decisions made for data cleaning in the Australian Longitudinal Study of Women’s Health (ALSWH) data.2 In 2002, limits were set for plausible weights, and the derived BMI variable and values outside these limits were set to missing.2 This decision was reviewed in July 2006 in light of analytical issues arising and it was decided that extreme values should no longer be deleted.2 Hence survey data from Survey 4 in 2006 onwards had less missingness in the weight and BMI data. The probability of missingness in our weight and BMI data is independent of the missing values given the observed data (i.e. it can be predicted based on the observed data). This satisfies the ‘missing at random’ mechanism and validates our analysis.3,4