Intervals and Confidence Limits

The intervals for values included around the mean ( la, 2a, etc.) are called confidence intervals and the percent probability of finding values within such a limit is termed confidence level. A usefiil graphical display of the relationship between these two quantities may be seen in Figiue 12.3. 

For example, in a data set describing a copper alloy having a mean (p) of 41.26 0.12 % (standard deviation) Cu, any future samples of the same alloy will yield results that will fall between 41.02 and 41.50% Cu (confidence interval is 2a) with a 96% probability (confidence level). An important corollary is that the chances that values outside these limits are 

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