Bureau of Transportation Statistics (BTS)
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Table 1 - Summary of Data Analysis Adopted for the 1990 and 1995 NPTS

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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