In the observational studies, the data are collected or recorded as they appear in the data generating units or individuals without intervening or influencing the data generating process. So, there is no imposition of external conditions or intervention or any other activities or treatments on the data generating units or individuals. An example of an observational study is to gather measurements on the blood sugar level of a group of patients as they are observed (without implementing any medical procedure or administering any drug to impact on the sugar level).