TABLE 1 - Comparison of Sampling Strategies,,,,,,,,
Sampling and estimation alternative,,Unstratified ratio estimation statistics,,,Overall performance,,,
,,"cv of 
pass-miles",cv of auxiliary variable,Correlation coeff between pass-miles and auxiliary variable,Unit cv,Necessary sample size (SS),SS reduction vs. Circular ,
—,Circular 2710.1A,,,,n.a.,549,,
A,Direct sampling and estimation,,,,0.95,522,5%,
B,Ratio estimation; auxiliary variable = boardings,0.95,0.77,0.67,0.72,296,46%,
C,Stratified ratio estimation (4 strata); auxiliary variable = boardings,,,,0.43,117,79%,
D,Combined ratio estimation; auxiliary variable = boardings,,,,0.45,117,79%,
E,Ratio estimation; auxiliary variable = (boardings * route length),0.95,0.91,0.89,0.44,112,80%,
F,Ratio estimation; auxiliary variable = (boardings * adjusted route length),0.95,1.09,0.89,0.51,147,73%,
G,Combined ratio estimation; auxiliary variable = (boardings * route length),,,,0.39,86,84%,
KEY: cv = coefficient of variation.,,,,,,,,