DOI: 10.5258/soton/d3556
title: Geographically weighted mediation analysis: food retail stores accessibility, deprivation and depression in Hampshire and the Isle of Wight [Dashboard]

description: This analysis applies a novel spatial mediation framework to examine how food retail accessibility mediates the relationship between deprivation and depression at the local level.

The methodological approach combines mediation analysis principles (Judd, C.M. & Kenny, D.A., 1981) with Geographically Weighted Regression (GWR) models, allowing relationships to vary spatially across Hampshire and the Isle of Wight rather than assuming uniform effects across the region.

The spatial mediation analysis involved two key steps: Step 1 established the total effect of income deprivation on depression, whilst Step 2 examined the indirect effect by modelling both deprivation and food retail accessibility as simultaneous predictors of depression. 

Local coefficients were then compared at each location to identify areas where food retail accessibility serves as a mediating pathway in the deprivation-depression relationship.

Statistical significance was assessed using local t-values with a threshold of ±1.96 (p &lt; 0.05), ensuring robust identification of meaningful mediation effects across different geographical contexts. The analysis utilised QOF depression prevalence data (2022), Index of Multiple Deprivation measures (2019), and Department for Transport travel time statistics to retail food outlets (2019), representing spatial access to food supply chain endpoints across the study region.

Data sources: 

In all analyses, we used the LSOA boundaries published by the Office for National Statistics:
Office for National Statistics. Census 2011 geographies [Internet]. 2020. Available from: Lower layer Super Output Areas (December 2011) https://geoportal.statistics.gov.uk/datasets/ons::lower-layer-super-output-areas-december-2011-boundaries-ew-bfc-v3/about

Digital vector boundaries for Integrated Care Boards in England were those published by the Office for National Statistics: Integrated Care Boards (April 2023) EN BGC [Internet]. 2023. Available from: https://www.data.gov.uk/dataset/d6bcd7d1-0143-4366-9622-62a99b362a5c/integrated-care-boards-april-2023-en-bgc

Depression Prevalence 2022 - QOF depression prevalence: Daras, K., Rose, T., Tsimpida, D., & Barr, B. (2023). Quality and Outcomes Framework Indicators: Depression prevalence (QOF_4_12) [Dataset]. University of Liverpool. Available from: https://datacat.liverpool.ac.uk/2170/

Retail accessibility: DfT. (2021). Journey time statistics, England: 2019 [Dataset]. Department for Transport. Available from: https://www.gov.uk/government/statistics/journey-time-statistics-england-2019/journey-time-statistics-england-2019#official-statistics

Deprivation: McLennan, D., Noble, S., Noble, M., Plunkett, E., Wright, G., & Gutacker, N. (2019). The English indices of deprivation 2019: Technical report. Available from:https://www.gov.uk/government/statistics/english-indices-of-deprivation-2019

Longitudinal Depression: Tsimpida, D., Tsakiridi, A., Daras, K., Corcoran, R., & Gabbay, M. (2024). Unravelling the dynamics of mental health inequalities in England: A 12-year nationwide longitudinal spatial analysis of recorded depression prevalence. SSM - Population Health, 26, 101669. Available from: https://doi.org/10.1016/j.ssmph.2024.101669