There are several ways to collect data from a sample and extrapolate the data to the entire population. The experimental study is a common method of data collection. Here, the samples are manipulated by applying some form of treatment before collecting data. Suppose a researcher wants to know the effect of sunlight on plant growth. In this experiment, one group of plants is exposed to sunlight, and another group is kept in the dark. After a month, the heights of the plants are recorded, and an inference– whether sunlight is required for plant growth–is drawn. Thus, in an experiment, the samples are manipulated before collecting the data. Clinical trials are typical examples of data collection by experiments. Before a drug or treatment method is released for public use, its efficacy is tested on a small number of randomly selected groups of volunteers. Here, one group of subjects is treated with specific doses of drugs or treatment methods, and a control group may be given a placebo. Then, the effects on disease symptoms are evaluated.