What is the probability of making a type II error typically set at?

The probability of making a type II error, often denoted as beta (β), is commonly set at 0.2 in research contexts. This choice implies that there is a 20% chance of failing to reject the null hypothesis when it is actually false. This threshold is frequently adopted in fields such as psychology to balance the risks of type I errors (false positives) and type II errors (false negatives).

Setting the probability of a type II error at 0.2 allows researchers to maintain a reasonable level of power in their studies, roughly translating to an 80% probability of correctly rejecting a false null hypothesis. This standard is often used in hypothesis testing to ensure that the study is adequately powered to detect an effect if it exists, thereby minimizing the risk of overlooking significant findings in research.