Statistics never proves a theory, but along with other beliefs, provides a basis upon which a scientist can make decisions. There are two primary means for collecting data. The essential difference consists of who assigns the treatments. In an experimental study, the researcher has control over the allocation, and in an observational study, the researcher has no control. The experimental unit is the smallest group of subjects in an experiment whose response cannot be affected by the other subjects.
Sample size is the number of units.
Begin a program to encourage compliance with vaccination recommendations. When a researcher conducts an experiment, she manipulates the independent variable and measures the dependent variable. These are ways of summarizing data that can reveal information, but are not usually used to test the validity of a hypothesis. Different types of descriptive data can often be presented graphically. An inferential statistic is a claim about a population that can be tested with data obtained from a random sample.