The right dose of data: balancing reliability and participant burden in a validated daily measure of food parenting practices

Intensive longitudinal methods are increasingly used to capture daily fluctuations in food parenting practices (FPP), but reliable tools for daily assessment are limited. Most studies rely on a fixed recall period for all FPP constructs; yet, the reliability of such approach remains unclear as some FPP may fluctuate more than others. Identifying the minimum number of measurement days needed can improve the feasibility and quality of daily FPP research. This Daily Diary study aimed to: 1) assess the test–retest reliability of daily FPP measures among mothers and fathers over a 14-day period; 2) estimate the minimum number of days needed to achieve adequate reliability; and 3) validate these reliability estimates using a second 14-day period. A total of 315 parents (aged 40 ± 5 years; 60% mothers) of children aged 2.5–6 years completed 28 daily assessments across two 14-day periods, three months apart, yielding 8820 observations. Seven FPP constructs were assessed daily using 13 binary items, and evidence of validity was obtained with a Confirmatory Factor Analysis (CFA). Intraclass correlation coefficients (ICCs) were calculated from mixed-effect models using data from the first 14-day period. The Spearman-Brown formula estimated the minimum number of days needed for ICC ≥ 0.70. These minimum-day estimates were validated using the second 14-day period, drawing random sets of consecutive and non-consecutive days. ICCs in the first period ranged from 0.80–0.97. Required days for acceptable reliability varied by FPP construct: Coercive control (1 day); Autonomy support, Child involvement, and Meal routines (5–6 days); and Rules and limits, Nondirective support, and Healthy opportunities (8–9 days). Compared to fathers, mothers required fewer days to reliably assess Rules and Limits, Healthy Opportunities, Autonomy and Nondirective Support. Validation in the second period showed ICCs ≥ 0.70 except for Healthy opportunities, Nondirective support, and Child involvement, which had borderline ICCs (0.63–0.68) in some subgroups and sampling approaches. This study provides a valid and reliable instrument to measure FPP in Daily Diary protocols. Although 14 days of data collection ensures high reliability, many FPP constructs can be assessed reliably with fewer days. To reduce participant burden, researchers may tailor diary duration based on the specific construct and caregiver sex.