Length of stay with its distribution and interval

Where alos() takes the total days and returns a mean, this takes one value per person and reports the spread as well, because a mean stay is a poor summary of a distribution that is usually skewed.

Usage

stay_summary(days_per_person, conf_level = 0.95)

Arguments

days_per_person

Days served, one element per person.

conf_level

Confidence level for the interval on the mean.

Value

A one-row data frame: n, total_days, mean, sd, median, iqr, max, se, lower, upper.

Details

The interval is the ordinary t interval on a mean. It describes uncertainty about the AVERAGE stay, not the spread of stays, and on a skewed distribution the median and the interquartile range say more about a typical stay than the mean does – which is why they are returned beside it rather than left to be asked for.

Lakner's caveat on alos() applies here too (1976, p.16-17): a person still held has an unfinished stay, so a window shorter than the longest stay biases the mean DOWNWARD.

See also

alos(), adp(), stock_flow()

Examples

# a skewed distribution: most stays short, a few long
stays <- c(rep(1, 40), rep(3, 30), rep(10, 20), 60, 90, 120)
stay_summary(stays)
#>    n total_days     mean       sd median iqr max       se    lower    upper
#> 1 93        600 6.451613 16.33183      3   2 120 1.693532 3.088113 9.815113

# the mean is pulled well above the median by the long tail
stay_summary(stays)[, c("mean", "median", "max")]
#>       mean median max
#> 1 6.451613      3 120