Sampling uncertainty in medical research J. Ranstam  Osteoarthritis and Cartilage  Volume 17, Issue 11, Pages 1416-1419 (November 2009) DOI: 10.1016/j.joca.2009.04.007 Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions

Fig. 1 A super- and a finite population of osteoporosis patients (symbolized by black and white dots; white dots representing some clinically meaningful characteristic; the finite population defined by the continuous frame). Two random samples of 50 patients each (the gray rectangles) have been drawn from the finite population. While the finite population has 10% white dots, sampling uncertainty is manifested in the sampled units by the varying proportion of white dots, one sample having 8% (4 of 50), the other one 16% (8 of 50). As the super-population is infinitely large it cannot be described graphically, but if the two finite samples can be assumed to be randomly sampled from the super-population, its proportion of white dots can be estimated to 8% (2.2%–19.2%) and to 16% (7.2%–29.1%), respectively. The range within brackets are 95% confidence intervals describing the sampling uncertainty. Osteoarthritis and Cartilage 2009 17, 1416-1419DOI: (10.1016/j.joca.2009.04.007) Copyright © 2009 Osteoarthritis Research Society International Terms and Conditions