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. 2006 May 10;114(10):1479–1485. doi: 10.1289/ehp.9101

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Sample size required to demonstrate a statistically significant effect (p = 0.01) 90% of the time for different magnitudes of response (effect size) and different proportions contributed by sensitive subpopulations. The ability to detect a small overall change when only a small proportion of the total population consists of responders requires extremely large sample sizes.