Monthly Archives: July 2012

What is Power Analysis?

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What is power in statistics, and how does it relate to the size of my sample?

This is a common question we hear from doctoral students doing quantitative analysis in their research. They may know who they want to survey or interview, but selecting the size of the sample is a mystery.  In this case, the tool to help you is power analysis.

Power analysis is a method to determine how large a sample is needed for statistical judgments that are accurate and reliable, and how likely the selected statistical test is to detect effects of a given size in a particular situation.  We just added a new resource to our library that steps you through the basics and points you to additional references on this very useful statistical tool.  You can find it here:

http://dissertationrecipes.com/wp-content/uploads/2011/04/Power-AnalysisX.pdf

 

Effect Size vs. Inferential Statistics

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What is the difference between a statistically significant result and a meaningful result?

Most doctoral students are exposed to the standard canon of quantitative research methods – null hypothesis testing using statistical inference.  Using a variety of different test methods, one can test hypotheses to determine whether or not relationships between variables exist, within a reasonable degree of error, and thereby whether or not a null hypothesis can be rejected or fail to be rejected.

While this sort of hypothesis testing is ubiquitous in research, a statistically significant result does not always equate with a meaningful result.  Particularly in large samples, statistical significance in a tested relationship can be present even while the effects of the variables on each other are minor, even trivial.  In such cases, we need a better approach to determine not just whether statistical significance is present, but whether the effects are sufficiently large to be important.

We have just added a resource to our “guides, tools, and worksheets” library that explores how measuring and reporting effect sizes can provide a stronger interpretation of a relationship between variables than the usual “p-value” approach in inferential statistics.   You can find the discussion here:

http://dissertationrecipes.com/wp-content/uploads/2011/04/Effect-SizeX1.pdf