Find the sample size required to estimate the true mean conc

Find the sample size required to estimate the true mean concentricity to within +-.2 using a 95% confidence interval.

Solution

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Kane (1986) discusses the concentricity of an engine oil sealgroove. Concentricity measures the cross-sectional coaxialrelationship of two cylindrical features. In this case, he studiedthe concentricity of an oil seal groove and a base cylinder in theinterior of the groove. He measures the concentricity as a positivedeviation using a dial indicator guage. Historically, the standarddeviation for the concentricity is 0.7. To monitor this process, heperiodically takes a random sample of three measurements.

Compute Sample Size
n = (Z a/2 * S.D / ME ) ^2
Z/2 at 0.05% LOS is = 1.96 ( From Standard Normal Table )
Standard Deviation ( S.D) = 0.7
ME =0.2
n = ( 1.96*0.7/0.2) ^2
= (1.37/0.2 ) ^2
= 47.06 ~ 48