TABLE 1 Summary of Data Analysis Adopted for the 1990 and 1995 NPTS,,,,,
Description of constraints,1990,1995,,,
Sample size—total trips,"159,832","381,388",,,
Reasons for dropping records,,,,,
Invalid destination,"3,314",43,,,
Trip in miles >200,"23,372","27,455",,,
Travel minutes >120,"3,015","5,254",,,
Age >65 years,"9,210","35,399",,,
Age <18 years,"21,470","63,832",,,
Shop duration >420,707,70,,,
Total dropped,"61,088","132,053",,,
Subtotal at trip level  (after records are dropped),"98,744","249,335",,,
Subtotal at person level ,"15,870","52,341",,,
"Travel + duration minutes >1,440","7,652",656,,,
"Travel + duration minutes <1,440","2,643","17,119",,,
Duration <0,654,"2,237",,,
Total dropped,"10,949","20,012",,,
Net total at person level,"4,921","32,329",,,