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Accounts Receivable

'From Mendenhall/Reinmuth/Beaver, 1992, p. 80)
'During times of economic recession, dentists and physicians tend to
'incur special problems with account collection. The number of days
'since billing 30 accounts receivable of a physician are shown below
'in vector A. Establish a 90% confidence interval for the average
'number of "days since billing" for all the physicians' accounts.
'Use the "bootstrap" procedure. If we could, we would take
'additional samples from the universe of accounts receivable.
'That is too time-consuming and too expensive. Instead, we let our
'sample serve as a proxy universe. We can imagine replicating
'each of the sample observations millions of times to creat our
'"bootstrap" universe. Even this is time-consuming, so we achieve
'the same effect by putting each observation back in after we
'sample it -- sampling with replacement. We draw samples of size 20,
'because this is the size sample whose behavior we wish to observe.

NUMBERS (17 57 10 35 26 3 21 11 7 
                    72 5 86 6 20 105 40 14 42 12 32) a
REPEAT 1000
  SAMPLE 20 a b

take a sample of 20 with replacement

  MEAN b c

find the mean

  SCORE c z

keep score

END

end the loop, go back to the repeat statement and repeat until all 1000 trials are complete.

HISTOGRAM z 
PERCENTILE z (5 95) k

find the interval that bounds 90% 'of the results.

PRINT k