After you perform an ANOVA, it is useful to be able to
report Omega Squared as a measure of the strength of the effect of the independent
variable. Stata does not have a program or option that computes this, but ATS has developed a program called
**omega2** that you can download and use to
compute Omega Squared after running an ANOVA. You can download the **omega2
**command by typing **search omega2 **(see
How can I use the search command to search for programs and get additional
help? for more information about using **search)**.

Once installed, you can use
**omega2**
after running an ANOVA. Below, we run an ANOVA where factor **b** has 4
levels and is highly significant.

anova y bNumber of obs = 32 R-squared = 0.8259 Root MSE = 1.21008 Adj R-squared = 0.8072 Source | Partial SS df MS F Prob > F -----------+---------------------------------------------------- Model | 194.50 3 64.8333333 44.28 0.0000 | b | 194.50 3 64.8333333 44.28 0.0000 | Residual | 41.00 28 1.46428571 -----------+---------------------------------------------------- Total | 235.50 31 7.59677419

We can now run **omega2** and we get a value of 0.8023.

omega2omega squared = 0.8023

Below we run a factorial ANOVA, and factor **b**
is again highly significant.

anova y a b a*bNumber of obs = 32 R-squared = 0.9214 Root MSE = .877971 Adj R-squared = 0.8985 Source | Partial SS df MS F Prob > F -----------+---------------------------------------------------- Model | 217.00 7 31.00 40.22 0.0000 | a | 3.125 1 3.125 4.05 0.0554 b | 194.50 3 64.8333333 84.11 0.0000 a*b | 19.375 3 6.45833333 8.38 0.0006 | Residual | 18.50 24 .770833333 -----------+---------------------------------------------------- Total | 235.50 31 7.59677419

When there is more than one factor present, you need to
supply **omega2** with the **SS** and **df **for
the effect you wish to compute Omega Squared. Below, we compute Omega Squared for
factor **b** by supplying the **SS** and **df** for
factor **b**.

omega2 194.50 3omega squared = 0.8134