In an observational study, the researcher observes and finds measures about a chosen sample — doing so without controlling its environment, nor interacting with or exposing it to any treatment. This method is used when it is impossible to isolate the variable under study or when individuals cannot be exposed to treatments due to ethical concerns.

An observational study aims to observe the effect of a risk factor, a treatment, or other intervention. The study's criteria needs to be specified in advance to find characteristics, behaviors, or specific events in the observations. Criteria, such as a list of things to look for, ensure consistency in the process of making observations.

It is crucial to acknowledge that other variables might affect a study. Suppose that a diet program's effect on a person's blood pressure is being investigated. It must be accounted for that there are various factors which also affect blood pressure such as a person's stress levels or exercise routine. Consider the following cases of advantages of observational studies.

Advantages	Example
Measures are taken in real and naturally occurring scenarios.	Observing lions in their environment to learn about roles, eating habits, and social and family structures.
It is helpful for complex situations, especially those where imposing treatment on individuals could be unethical.	Compare the sugar levels of $50$ people who drink coffee and $50$ who do not without influencing this decision.

Observational studies also have disadvantages to be considered.

Disadvantages	Example
Risk of ignoring other factors that can affect the variables of the study.	A study might conclude that people who meditate have lower cholesterol levels than others, but it might ignore that they exercise more and follow a healthier diet than others.
It can be time-consuming, mainly if the observed variables do not occur frequently or last for long periods.	Studying the lifestyle of elephants in their birth and pregnancy stages. Their pregnancy can last around two years and they give birth around every four years.

In conclusion, consider the context of what is under study to be sure that an observational study is the best methodology for data collection.