The matching functions fullmatch and pairmatch
have a maximum problem size, based on the number of comparisons between treated
and control units. For a completely dense problem, in which every treated units
is compared to every control unit there are length(treated) *
length(control) comparisons. A caliper restricts which comparisons are valid,
disallowing matches of treated and control pairs that are too far apart. A
caliper can significantly decrease the size of a matching problem. The
caliperSize function reports exactly who many valid treated-control
comparisons remain after applying a caliper of the given width.
caliperSize(scores, z, width, structure = NULL)A numeric vector of scores providing 1-D position of units
Treatment indicator vector
Width of caliper, must be positive
Grouping factor to use in computation
numeric Total number of pairwise distances remaining after the caliper is placed.