Modified ground-truthing: an accurate and cost-effective food environment validation method for town and rural areas

Table 1 Accuracy of three food retail outlet lists, as compared with ground-truthing

		List 1: Business Analyst (BA)				List 2: Modified ground-truthing,^a (stores outside of clusters assumed open)				List 3: Modified ground truthing,^a (stores outside of clusters assumed closed)
		Site				Site				Site
		A	B	C	Total	A	B	C	Total	A	B	C	Total
Stores on list	for comparison with traditional ground-truthing	14	74	63	151	15	78	60	153	14	66	46	126
True positives	stores correctly listed	7	48	35	90	14	69	49	132	14	66	46	126
False positives	stores that should not have been on the list	7	26	28	61	1	9	11	21	0	0	0	0
False negatives	stores missing from the list	7	24	15	46	0	3	1	4	0	6	4	10
					Mean				Mean				Mean
Positive Predictive Value (PPV)	true positives/(true positives + false positives)	0.50	0.65	0.56	0.57	0.93	0.88	0.82	0.88	1.00	1.00	1.00	1.00
Sensitivity	true positives/(true positives + false negatives)	0.50	0.67	0.70	0.62	1.00	0.96	0.98	0.98	1.00	0.92	0.92	0.95

^aThe list of stores derived from driving only the streets within 1/8 mile buffer of any two stores on the commercial list