A statement made about a population for testing purposes is called a **hypothesis**. A hypothesis is a tentative explanation for a phenomenon that can be tested through observation or experiment. Hypotheses are often expressed in the form of “If…, then…” statements, such as “If a new drug is effective, then it should reduce the symptoms of a disease.”

There are two main types of hypotheses: the **null hypothesis** (H0) and the **alternative hypothesis** (H1). The null hypothesis is the assumption that there is no difference between two groups or that there is no effect of a treatment. The alternative hypothesis is the opposite of the null hypothesis, and it states that there is a difference between the groups or that there is an effect of the treatment.

Hypotheses are tested using statistical methods. These methods allow researchers to determine whether the data they have collected is consistent with the null hypothesis or the alternative hypothesis. If the data is not consistent with the null hypothesis, then the null hypothesis is rejected. This means that there is enough evidence to support the alternative hypothesis.

Hypothesis testing is a fundamental tool in scientific research. It allows researchers to test their ideas and make progress in understanding the world around us.