Researchers are aware of these problems. In fact, they take this into account when studying the patient’s answers. For example, remembering past information is referred to as recall. Scientists already know there is a certain amount of bias just based on answers that rely on memory.

The researchers also take into account the fact that every test has its own problems. Scientists know how to account for changes in the test score that are based on errors in the test itself. This is called the standard error of measure.

Patients are usually instructed to fill out the forms to the best of their ability. The math formulas used to analyze the data will do the rest.