To improve reliability and validity of a baseline physical activity assessment, which approach is best?

• A. Relying on a single self-report diary with no piloting
• B. Collecting data only once without clear definitions
• C. Using informal interviews without validated measures
• D. Using validated instruments and standardized administration

Answer: (D)

Using validated instruments with standardized administration provides established reliability and validity, and minimizes variation due to how data are collected. When you rely on a single self-report diary with no piloting, you introduce recall errors, misunderstandings of the diary items, and unknown measurement properties—the results can vary widely between people or even for the same person at different times. Collecting data only once without clear definitions invites misclassification and inconsistent interpretation of what counts as activity, how long, and at what intensity, making the baseline unreliable. Informal interviews without validated measures bring about interviewer bias and lack of documented psychometric properties, so it’s hard to know whether the questions and responses truly capture physical activity in a consistent way. In contrast, validated instruments have been tested for reliability (yielding stable results over time and across raters) and validity (accurately reflecting the construct of physical activity). Standardized administration ensures every participant receives the same prompts, timing, and instructions, reducing systematic error and enabling meaningful comparisons across individuals and over time. This combination yields a robust baseline that can faithfully guide subsequent behavior-change efforts.