jtdecay
Distance-decay functions for journey to crime
jtdecay(d, type, par, tab = NULL)The decay of the chance of offending with distance from an offender’s
base, in the forms of Brantingham and Brantingham (1981), Rossmo (2000)
and Levine (2009): "linear", f = max(0, A + B d), par = c(A, B);
"negexp", f = A exp(-b d), par = c(A, b) with b >= 0;
"normal", f = A dnorm(d, mu, s), par = c(A, mu, s); "lognormal",
f = A dlnorm(d, mu, s), par = c(A, mu, s) (the lognormal density of
d; some texts use log d^2 and 1 / d^2, which is not a density);
"trunc", the truncated negative exponential, f = P d / dp up to the
peak dp and P exp(-C (d - dp)) beyond, par = c(P, dp, C); and
"table", values tab at distances 0, delta, 2 delta, ..., linear in
between and 0 beyond, par = delta (as jtcal() tabulates).
Parameters
Section titled “Parameters”dDistances: numbers from 0.
typeThe form: one of the names above.
parThe parameters of the form, of the length given above.
tabFor
type = "table": at least two values from 0.
Returns
Section titled “Returns”A numeric vector of f(d), one per distance.
References
Section titled “References”Brantingham, P. J. and Brantingham, P. L. (1981). Environmental Criminology. Sage.
Levine, N. (2009). Introduction to the special issue on Bayesian journey-to-crime modelling. Journal of Investigative Psychology and Offender Profiling, 6(3), 167-185. doi:10.1002/jip.107
Examples
Section titled “Examples”jtdecay(c(0, 0.5, 1, 2, 5), type = "trunc", par = c(1, 0.5, 0.8))Generated from the R help page: jtdecay in the R reference.