The theory behind the Chi2 test

Most textbooks do a pretty bad job in describing how the Chi² test works and how to apply it.

Here's my first video on the subject.  It goes into the theory behind the Chi² formula and when you would apply the statistic to your data.  The components of the Chi² formula are discussed so you should be able to get an idea what it measures.  

The Chi² test is commonly taught in Genetics courses to give students a tool to assess whether data could belong to particular ratios (e.g. 3:1, 1:2:1, 9:3:3:1). After viewing this video, you should:

•  recognize that the Chi² formula measures deviation of and observed value from a theoretical value for purposes of comparison
• be able to calculate the Chi² score from a set of data
• determine the degrees of freedom for a particular sample 
• be able to reject or fail to reject a set of data from a theoretical population by using the Chi² table

Actually doing the Chi²  test is quite simple.  I'll provide a few examples of calculating the Chi² value and interpreting it using the Chi²  table.