Sample Size Calculator in Excel |
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Jay Arthur
We help people think! Copyright © 2008
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To calculate a sample size you need to know:
The QI Macros Sample Size Calculator is designed to work with both variable (measured) and attribute (counted) data. When you click on QIMacros-Sample Size Calculator for Lean Six Sigma and Analysis Tools and select Sample Size Calculator, you should see the following:
The defaults are set to standard parameters:
Confidence Level Step 1 - Select a confidence level Confidence Interval Step 2 - Set the confidence interval Attribute (Counted) Sampling Step 3 - Attribute data - Set percent defects to 0.5 Variable (Measured) Data If you know the specification tolerance, then you can use (maximum value - minimum value)/6 as your standard deviation. (The default is 1/6=.167). Step 3 - Variable Data - Enter Standard Deviation Step 4 - Enter the total population (if known) Step 5 - Press Calculate
Step 6 - Read the Sample Size In this case, we're using variable data so the sample size would be 43. Attribute Example:
Here you'd need 384 coins to be 95% confident that the coins fell within the 5% interval. What if you knew there were 1000 coins in the vat (population known)?
What if you changed the confidence interval to be +10% (0.1)?
You only need 88 to be 95% confident. Variable Example Estimated standard deviation = (2.027-2.009)/6 = .003 And you want to be 95% confident that the sample is within 0.001 of the true mean. Enter the data as shown below:
You need 35 samples. The Sample Size Calculator is just one of the tools included in the QI Macros for Excel SPC Software for Excel. |
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