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CRIMLAB

vodtst

Veil-of-darkness test

vodtst(day, night = NULL, ref = 1, shift = NULL)

Compares each group’s share of stops made in daylight, when a driver’s race can be seen, with its share in darkness, when it cannot. The ratio of the two odds against a reference group is the factor by which visibility changes that group’s chance of being stopped; 1 means no change.

Parameters

Section titled “Parameters”
day

Stops by group in daylight: non-negative numbers, as a numeric vector, a 1-d table, a list of single numbers or a one-row data frame. With night left out, one table of groups by stops: a matrix, 2-d table or data frame whose two columns are named day and night, in either order (columns are never taken by position).

night

Stops by group in darkness: positive numbers, in the forms of day; named inputs are matched to day by name, and an error lists any group named in one and not the other. Unnamed inputs are matched by position: only names protect against a mismatch.

ref

The reference group, by name (matched exactly, case included; a factor by its label) or by position in day as given.

shift

NULL, or one positive number per group: daylight exposure over darkness exposure, in the forms of day, matched by name.

Returns

Section titled “Returns”

A data frame with one row per group, in the order of day: group, ref (TRUE for the reference group), shday, shnight, ratio, sign (the sign of shday - shnight) and, when shift is given, adj.

Notes

Section titled “Notes”

The ratio identifies the visibility effect only when the mix of drivers on the road is the same in daylight and darkness. shift states how much each group’s exposure differs between the two, and adj is the ratio with that difference taken out. See proof("vodtst").

References

Section titled “References”

Grogger, J. and Ridgeway, G. (2006). Testing for racial profiling in traffic stops from behind a veil of darkness. Journal of the American Statistical Association, 101(475), 878-887. doi:10.1198/016214506000000168

Examples

Section titled “Examples”
vodtst(day = c(white = 600, black = 400),
       night = c(white = 700, black = 300))
# one table of groups by day and night
stops <- data.frame(day = c(600, 400), night = c(700, 300),
                    row.names = c("white", "black"))
vodtst(stops)

Generated from the R help page: vodtst in the R reference.