Bias can occur in sampling. bias refers to

Bias can happen in sampling. The propensity of a sample statistic to systematically under - or over-approximate a population is referred to as bias.

To add, in statistics, sampling bias is a bias in which a sample is collected in such a way that some members of the intended population are less likely to be included than others.

The following are some types of biases in Statistics:

Selection bias includes individuals being more likely to be chosen for study than others, biasing the sample. This can also be termed Berksonian bias

In statistical hypothesis testing, a test is said to be unbiased if for some alpha level (between 0 and 1), the probability the null is not accepted is less than or equal to the alpha level for the entire parameter space defined by the null hypothesis, while the probability the null is rejected is greater than or equal to the alpha level for the entire criterion space interpreted by the alternate hypothesis.