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Confidence function
I need to know about the output of the confidence funtion in Excel. I used
the expression... =confidence(0.01, STDEV, 164). The stdev changes for every row of data and I want the 99% confidence level. The sample size is 164. The result from the calculation for the funtion is one number which changes with every row. What does this number mean? |
#2
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Confidence function
Mike -
Regarding the explanation of the CONFIDENCE worksheet function in Excel's Help, what don't you understand? CONFIDENCE gives the half-width of a confidence interval. It is based on the normal distribution, and it is appropriate when the population standard deviation is known, i.e., when the standard deviation does not have to be estimated from the sample data. If sample data are used to estimate standard deviation, the confidence interval should be computed using the t distribution, not the normal distribution. According to the book "Data Analysis Using Microsoft Excel: Updated for Office XP" by Michael R Middleton, the half-width is =TINV(1-Conf_Level,n-1)*STDEV(Data)/SQRT(n) For your example, that would be =TINV(0.01,163)*STDEV(Data)/SQRT(164) What does it mean? The half-width and the sample mean are used to construct a confidence interval from (mean - half-width) to (mean + half-width). Referring to the Middleton book, here are two interpretations. Subjective Probability Interpretation: Based on the sample there is a 99% chance that the population mean is between (mean - half-width) and (mean + half-width). Relative Frequency (classical statistics) Interpretation: If we repeatedly selected random samples of size 164 from this population and constructed a confidence interval for each sample, approximately 99% of the confidence intervals would contain the true population mean. - Mike www.mikemiddleton.com "Mike Fisherow" <Mike wrote in message ... I need to know about the output of the confidence funtion in Excel. I used the expression... =confidence(0.01, STDEV, 164). The stdev changes for every row of data and I want the 99% confidence level. The sample size is 164. The result from the calculation for the funtion is one number which changes with every row. What does this number mean? |
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