The effect of sample size on normative values

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Abstract
As shown by successively‐larger random samples of data on weight, length and head circumference with Ns of 25, 100, 400, 900, 1600 and 2500, respectively, and calculated values for percentiles 2.5, 5, 10, 15, 50, 85, 90, 95 and 97.5 sample size must range from a minimum of 25 to effectively distinguish the 10th from the 50th percentile, to 1300 to distinguish the 2.5th and 5th percentiles at the 95 percent confidence limits. From these randomly‐generated examples arranged by doubling values of N, and from theoretical calculations, nearly all published “norms” and standards are based on age/sex samples of inadequate size for the intended purpose.

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