# Can higher level be insignificant but lower level significant in a nested ANOVA?

I have ran a nested ANOVA on a data set and the results suggest that there is an association for the higher level with an insignificant P-value but also an association for the lower level with a significant P-value. Is this even possible, or have I done something completely wrong?

Details

I have a data set comprising of: Groups (A,B,C...) - each group contains 3 different genotypes (1,2,3...). The same genotype doesn't occur in two different groups. For example, I have group A with genotypes 1,2,3 and Group B with genotypes 4,5,6, and group C with genotypes 7,8,9. I then have several measurements of height for each genotype. I had to perform an analysis that can test for differences between the three groups as well as for the genotypes within each of the groups. I chose nested ANOVA, but now I'm slightly doubting myself. A huge thank you for any help!

• Basically I have a data set comprising of: Groups (A,B,C...) - each group contains 3 different genotypes (1,2,3,..). The same genotype doesn't occur in two different groups. I then have several measurements of height for each genotype. I had to perform an analysis that can test for differences between the three groups as well as for the genotypes within each of the groups. I chose nested ANOVA, but now I'm slightly doubting myself. A huge thank you for any help! – sshelp Nov 26 '12 at 11:50
• Sorry, I didn't make it quite clear: I have group A with genotypes 1,2,3 and Group B with genotypes 4,5,6, and group C with genotypes 7,8,9. – sshelp Nov 26 '12 at 16:56
• you can delete these comments now... I edited the question because I don't think you can with your reputation. Now that we have details, do you mean groups is the higher level and genotypes is the lower level? – John Nov 26 '12 at 17:06

This can happen a number of ways. You need to examine your outcome variables to see what happens but imagine something like the following.

height group gene
200    A     1
150    A     2
150    A     3
200    B     4
150    B     5
150    B     6


It's easy to see how gene's 1 and 4 lead to greater heights but there's no difference between the groups.