In a study patients of both CA stomach and CA colon

In a study patients of both CA stomach and CA colon were compared and their preoperative notes were studied for history of h. pylori. What type of study is this Cohort or Case control

Based on the given information, it is not possible to determine whether the study is a cohort or case-control study.

A cohort study would involve following a group of patients with a certain characteristic (such as H. pylori infection) over time to determine if they develop a specific outcome (such as gastric or colon cancer). A case-control study, on the other hand, would involve comparing patients with a certain outcome (such as gastric or colon cancer) to a control group without the outcome to determine if there is a difference in exposure to a certain risk factor (such as H. pylori infection).

The information provided in the question only indicates that the preoperative notes of patients with gastric and colon cancer were compared with regard to the history of H. pylori infection. It is possible that this could be part of a larger cohort or case-control study, but it is also possible that it is simply a comparison of two groups without a specific study design.