**Subject:** Book drops Sampling

From: James W. Mason <*masonjw*>

Date: Wednesday, March 13, 1991

Date: Wednesday, March 13, 1991

At Kansas State we have two outside bookdrops, one for walk up and one for drive up. Both are locked anytime the library is open. This has been the case "always." Complaints are few and most of those are because our parking is very limited, forcing people to leave their car standing while going inside. Of course, AV materials are never to be returned in the drops. While i've got everyone on the phone, we're going to do a condition survey similar to that at Stanford and U. Illinois. statistically speaking, how does 400 samples sound for a collection of 800,000? thanks. jim **** Moderator's comments: Short answer: it sounds fine. Medium answer: For dichotomous variables (ie yes/no), a sample size of 384 will yield a 95% confidence interval with a width of NO MORE THAN 5 percentage points. This is the "worst case". If your actual data has an increased variance (or in English, if the number of yeses is not pretty close to equal to the number of no's), the interval width will be even less. This holds true for infinite samples. If your population is very small (so that 384 is more than about 5% of the population) you can apply the finite population correction to reduce the interval even further. Does this mean that 400 specimens (the entire group is the sample, not the individual items) is an 'adequate' sample? Yes, if you are going to ask one dichotomous question. Maybe, if you are going to try to draw elaborate correlations, do crosstabs, etc, in which case you may not have enough observations in a particular category to draw meaningful conclusions. If you are looking at continuous data, then these remarks still obtain, if The Usual Assumptions about the underlying population are valid (ask your local statistician about this). Long answer: ask again when I'm chatty *** Conservation DistList Instance 4:48 Distributed: Thursday, March 14, 1991 Message Id: cdl-4-48-003 ***Received on Wednesday, 13 March, 1991