Background Public Health England recently published a tool to help local authorities monitor the density of fast food outlets, with restrictions on access to these ‘unhealthy’ outlets being promoted in the fight against obesity. Secondary data containing the locations of food outlets present valuable resources to guide and evaluate these interventions. However, evidence appraising these data sources is limited. This study therefore seeks to validate two sources of secondary food environment data (SFED): Ordnance Survey Points of Interest (POI) data and food hygiene data from the Food Standards Agency (FSA), against street audits. These data sources are commonly used in research, with the former also being used in the Public Health England tool.
Methods Audits were conducted across 54 Lower Super Output Areas in England. All streets within each Lower Super Output Area were covered to identify the name and street address of all food outlets therein. Audit identified outlets were matched to outlets in the SFED to identify true positives (TP: outlets in both the SFED and the audits), false positives (FP: outlets in the SFED only) and false negatives (FN: outlets in the audits only). Agreement was assessed using positive predictive values (PPV: TP/(TP +FP)) and sensitivities (TP/(TP +FN)). Confidence intervals were calculated in Excel using the Agresti-Coull method.
Results Overall, the street audits identified 1188 food outlets, compared to 1102 and 1098 for the POI and FSA data respectively. Sensitivity and PPV were significantly higher for FSA data (sensitivity: 0.80, CI: 0.77–0.82; PPV: 0.86, CI: 0.84–0.88) than for the POI data (sensitivity: 0.73, CI: 0.71–0.76; PPV: 0.79, CI: 0.77–0.81). Both datasets had ‘good’ agreement with street audits according to the Paquet classifications (‘good’ defined as PPV and sensitivities between 0.71 and 0.90).
Conclusion This study provides new evidence for the validity of SFED commonly used in research and emergently used by policymakers. Agreement between the SFED and street audits is sufficiently good to provide local authorities with confidence in using tools and research based on these SFED. Whilst FSA data has statistically significantly higher agreement with street audits than POI, the magnitude of the difference is relatively small. POI also has other advantages (e.g. more detailed outlet classifications and better spatial accuracy). Thus, POI is still a useful and recommended source of food environment data.
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