In researches where two or more groups are desired to be compared, observational and randomized experiments are very frequently used. As the subjects arc randomly assigned to the groups in randomized experiments, balance is provided in observed/unobserved covariates of subjects in different groups. As the subjects cannot be randomly distributed into groups in observational studies, balance of observed/unobserved covariates between groups is not provided. This situation causes a biased estimate of the treatment effect. In this research, it is focused oil different matching methods in observational studies and elimination of observed covariate effects confounding in the group effect, and these methods arc examined comparatively. For this purpose, the effect of depression in 300 migraine patients, obtained from an observational study, oil State continuous anxiety scale scores is taken and compared with the five different matching methods. Sensitivity of results is examined and it is researched whether the effect of treatment contains any bias. When results are examined, it is seen that matching methods produce similar results due to the overlap of propensity distribution in groups, high and balanced number of subjects in groups and covariates being not so many in number. The effects of unobserved covariates do not change the effect of treatment significantly. In conclusion, it is seen that, in the estimation of group effect in observational Studies, it is possible to eliminate the effects of observed covariates using matching methods and matching quality of matching methods based on the propensity score is high. (C) 2007 Elsevier Ltd. All rights reserved.