I am conducting an impact study, which is a "pure natural experiment" type. However, the sample size of the treated group is somewhat higher that the comparison group. Does this ratio difference affect the estimates of propensity score matching model result? If so, what proportion is better?
Hi Erkie,
The ratio of the sample sizes is not the primary issue. What is most important is that any comparison of means requires the estimation of means from each group. The goodness of the comparison is limited by the least accurate group estimation. Thus, the variance of the distribution of the sample mean of the group with the smallest n is the limiting factor and greatly impacted by the size of the n. As long as you have a large enough sample to estimate the mean of that group with accuracy you desire, you should be OK.
Good luck,
J. McLean
Hi,
It depends on which statistical analysis you would use.
If you're using ANOVA or t-test, besides small sample size, it might cause problems with the variance of each group.
However, you can perform a F-test of equality of variances or Levene's test.
Good luck,
Shay.
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