Average length of stay

The mean number of person-days served per person: the FLOW side of the same person-days.

Usage

alos(days, n)

Arguments

days

Person-days served during the period, summed.

n

Number of people. For an unbiased average this should be the people both admitted AND released within the period, because anyone still held has an unfinished stay.

Value

A single number: days per person.

Details

Lakner's \(\bar{X}_t = \sum X_i / N'\) (1976, p.16), with a caveat worth repeating (p.16-17): the period must be longer than the longest stay people actually serve, or the average is biased DOWNWARD, since the longest stays are the ones that fail to finish inside the window. For short-stay facilities a year is comfortable; for long sentences it is not, and the period has to be set from the records.

References

Lakner, E. (1976) A Manual of Statistical Sampling Methods for Corrections Planners. University of Illinois at Urbana-Champaign.

See also

adp(), stock_flow()

Examples

# Lakner (p.17): 2,700 inmates admitted and released served 12,150
# detention days between them.
alos(12150, 2700)
#> [1] 4.5