I am performing an analysis (for dissertation project) where I am comparing the sum of branch lengths from phylogenetic trees reconstructed from altered datasets (Group 0) versus sum of branch lengths from phylogenetic trees reconstructed from control datasets (Group 1). Then I am considering the observed values (the actual branch lengths from each tree) versus the expected values (the branch lengths from the control trees). The data is below:

Group Observed Expected

.00 1.50 3.01

.00 3.58 9.98

.00 1.00 4.00

.00 3.03 7.61

.00 2.52 6.41

.00 .91 3.13

.00 2.74 4.10

.00 1.89 4.44

.00 1.79 3.42

.00 2.11 3.74

.00 .52 1.60

1.00 3.01 3.01

1.00 9.98 9.98

1.00 4.00 4.00

1.00 7.61 7.61

1.00 6.41 6.41

1.00 3.13 3.13

1.00 4.10 4.10

1.00 4.44 4.44

1.00 3.42 3.42

1.00 3.74 3.74

1.00 1.60 1.60

After finding the regression lines for each group, I get two lines...for the control group, y = 1x, as expected since the values were plotted against each other, and the expectation is that of no change from the control tree group. For the altered group, y = 0.343x + 0.356. To find out if the slopes are statistically significantly different, I used SPSS (Analyze -> General Linear Model ->Univariate) to identify whether or not there was an interaction between the covariate (expectation) and the IV (group). The interaction term is statistically significant (p < 0.0005), indicating a violation of homogeneity of regression slopes.

**My question is**, by doing this analysis, am I able to report that the slopes are statistically significantly different? I think that lack of homogeneity between regression slopes is the same as them being statistically significantly different, but I wanted to run it across the forum to make sure I am correct.

Thank you.