1. Chi Square Review

2. When do I perform a Chi Square test?
Chi square tests are used to calculate a critical value when you are determining if your data matches an expected value.
In our Heredity Lab, the tobacco seeds we used were bred to give a green:1 albino ratio. This is our expected value.
The data we collect from our various experimental groups will be our observed values.

3. The Null Hypothesis Our Null says that the IV has NO effect on the DV
In other words, the experimental group ratios will not be significantly different from the expected 3:1 ratio
If a Chi Square Test indicates you should reject the Null, then there IS a significant difference between the expected ratio and the experimental group ratio(s)

4. The Chi Square Table Group % observed (o) % expected (e) (o-e) (o-e)2
(o-e)
(o-e)2
(o-e)2/e
% Control Group (light)
% Experimental Group (your IV)
% Total cells (same for both)
X2 = sum (o-e)2/e =

5. Degrees of Freedom (df) = # of groups minus one

6. What do I do with the Chi Square Value?
If the calculated chi-square value is greater than or equal to this critical value, then the two groups ARE significantly different, and the null hypothesis is rejected. If the null hypothesis is rejected and we are 95% confident that there is significant difference in the ratio of the experimental group from the expected 3:1
If the calculated chi-square value is less than this critical value, then the two groups are NOT significantly different, and the null hypothesis is not rejected/accepted.