This research conceptualises, measures and evaluates the effects of sample
selection bias on models of commuting time. Data are drawn from the Public
Use Microdata Sample of the 1990 US Census for the Boston metropolitan area
. The major finding of the analysis is that the process that determines ent
ry into employment introduces sample selection bias into the estimates of c
ommuting-time models. The degree of sample selection bias observed differs
by race/ethnicity and gender on such key variables as marital and parental
status and reliance on public transport, because the influence of these var
iables on employment differs by race/ethnicity and gender, These variables
are important for evaluating both the spatial mismatch and the spatial entr
apment hypotheses and therefore the contribution of previous analyses shoul
d be reconsidered.