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Effective Size

Source: R/esize_m.R
esize_m.Rd

Function for computing Effective Size

Usage

esize_m(lineup_tab, k, both = FALSE)

Arguments

lineup_tab

A table of lineup choices.

k

Number of members in the lineup. Must be specified by the user (scalar).

both

Logical. Defaults to FALSE, returning Tredoux's adjusted effective size estimate only. If TRUE, both Malpass's (1981) original formulation and Malpass's adjusted version (Tredoux, 1998) are printed to the console.

Value

The Tredoux-adjusted Malpass effective-size estimate. With both = TRUE, the original and adjusted estimates are also printed.

Details

Reduces the size of a lineup from a (corrected) nominal starting value by the degree to which members are, in sum, chosen below the level of chance expectation.

References

Malpass, R. S. (1981). Effective size and defendant bias in eyewitness identification lineups. Law and Human Behavior, 5(4), 299-309.

Malpass, R. S., Tredoux, C., & McQuiston-Surrett, D. (2007). Lineup construction and lineup fairness. In R. Lindsay, D. F. Ross, J. D. Read, & M. P. Toglia (Eds.), Handbook of Eyewitness Psychology, Vol. 2: Memory for people (pp. 155-178). Mahwah, NJ: Lawrence Erlbaum Associates.

Tredoux, C. G. (1998). Statistical inference on measures of lineup fairness. Law and Human Behavior, 22(2), 217-237.

Tredoux, C. (1999). Statistical considerations when determining measures of lineup size and lineup bias. Applied Cognitive Psychology, 13, S9-S26.

Wells, G. L.,Leippe, M. R., & Ostrom, T. M. (1979). Guidelines for empirically assessing the fairness of a lineup. Law and Human Behavior, 3(4), 285-293.

See also

esize_T, whose “Small-sample bias” section describes a downward bias affecting plug-in effective-size estimators at small numbers of choices, and an optional correction.

Examples

#Data:
lineup_vec <- round(runif(100, 1, 6))

#Call:
esize_m(lineup_vec, 6, both = TRUE)
#> Effective size (Malpass, 1981) =  4.84 
#> Effective size (Malpass, 1981, 
#>              adj Tredoux, 1998) =  4.84 
#> [1] 4.84
esize_m(lineup_vec, 6)
#> [1] 4.84