# P-value when sample SDEV differs from population
**URL:** https://boards.straightdope.com/t/p-value-when-sample-sdev-differs-from-population/681151
**Category:** Factual Questions
**Created:** [February 12, 2014, 3:24pm UTC](https://boards.straightdope.com/t/p-value-when-sample-sdev-differs-from-population/681151 "2014-02-12T15:24:00Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Reyemile](https://boards.straightdope.com/u/Reyemile)
#### Post date: [February 12, 2014, 3:24pm UTC](https://boards.straightdope.com/t/p-value-when-sample-sdev-differs-from-population/681151/1 "2014-02-12T15:24:00Z")
If a sample or sub-population has the same mean as, but a different standard deviation from, the general population, how do I test whether this difference is significant?
For example: I purchased a hamburger machine from a line of machines known to produce 100g beef patties with a standard deviation of 5g. The average weight of my first 100 patties was not significantly different from 100g, but the standard deviation of the batch was 9g. Can I conclude my machine is defective, and if so, what is the p-value of my conclusion?
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### Author:  [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)
#### Post date: [February 12, 2014, 3:29pm UTC](https://boards.straightdope.com/t/p-value-when-sample-sdev-differs-from-population/681151/2 "2014-02-12T15:29:54Z")
Use a chi-square test.
[http://www.itl.nist.gov/div898/handbook/eda/section3/eda358.htm](http://www.itl.nist.gov/div898/handbook/eda/section3/eda358.htm)
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### Author:  [@Reyemile](https://boards.straightdope.com/u/Reyemile)
#### Post date: [February 12, 2014, 3:31pm UTC](https://boards.straightdope.com/t/p-value-when-sample-sdev-differs-from-population/681151/3 "2014-02-12T15:31:28Z")
Well that was easy 🙂