**Subject:** Sampling

From: Karen Brynjolf Pedersen <*karen.brynjolf.pedersen*>

Date: Thursday, November 22, 2001

Date: Thursday, November 22, 2001

Pierre-Emmanuel Nyeborg <penyeborg [at] noos__fr> writes >I am having trouble figuring out the size of the sample we should >examine to get an accurate view of the problems. And I also have >problems figuring out the time needed for the examination of each >sample. I would appreciate any suggestion, remarks or advice. I have used the method of Carl M. Drott to make surveys of different photographic collections. The statistical method is founded on the principle of random selection and is described in his article "Random Sampling: a Tool for Library Research" in College and Research Libraries, March 1969 p.119-125. In his article is a table showing different options regarding the size of the samples, depending on how you want the tolerance and the confidence of the survey. For instance if you want your survey to have a 90% confidence and a 7% tolerance, your sample size should be 138, according to the table. The confidence is the probability that the answer is right. If the confidence is 90% this means that if you repeat the survey 100 times, you will get the same result 90 times out of 100.The tolerance is the accuracy of the survey, for instance plus/minus 7%. I think the article makes an excellent help for surveying collections. If you cannot find the article, I will be happy to Fax: it to you. As for the time being used on the survey, I think most time is spent on the planning of the survey and an accurate description of damages, photographic technique et cetera to describe each sample. How much time you use of course depends on how much information you want from each sample and how the collection is organised. If your collection consists of various housing systems you might want to take for instance 138 samples of each type of storage system. I can tell you that I have used about 200 hours to take samples from a collection with 7 different storage systems each containing various kinds of negatives and prints, and 138 samples were taken from each storage system. The time spent includes planning the survey, taking the samples, and analyzing the results, but not writing a report which still awaits (alas). I hope this can give you some ideas for your survey--I am sure there are other ways to do this. Karen Brynjolf Pedersen Conservator of Photographs Department of Conservation The National Museum of Denmark Brede P O Box 260 DK-2800 Lyngby Denmark +45 33 47 35 51 Fax: +45 33 47 33 27 *** Conservation DistList Instance 15:39 Distributed: Tuesday, November 27, 2001 Message Id: cdl-15-39-011 ***Received on Thursday, 22 November, 2001