Ascertainment bias involves which kind of assumptions?

• A. Assumptions including stereotypes such as racism or ageism
• B. Relying on a random sample
• C. Using objective measurements
• D. Following clinical guidelines

Answer: (A)

Ascertainment bias arises when preconceived expectations shape how data are observed or recorded. If a clinician or researcher believes that a certain group is more or less likely to recover, they may notice, interpret, or document outcomes in that group differently, which skews the data toward those expectations. This kind of bias often stems from stereotypes, such as racism or ageism, influencing what is recognized or recorded.

Relying on a random sample helps ensure representativeness and reduces selection bias, using objective measurements minimizes subjective judgment, and following clinical guidelines promotes consistency in assessment. These practices tend to prevent bias rather than introduce it, which is why the statement about assumptions including stereotypes is the best fit for ascertainment bias.