Medical Research: Validity, Bias, Confounds, Probability, P-value, and Power

Kimberly Pendell

Validity

Validity implies that the measurement reliably measures what it intends to measure.

Validity relates to the magnitude of bias.

Bias

Bias is the systematic tendency to produce an outcome that differs from the underlying truth.

Some different types of bias

Selection bias Interviewer bias Recall bias Detection bias Verification bias Publication bias

Bias and Research Designs

Ex. research design

Ex. of potential bias

Ex. of potential solution

RCT Selection bias Randomization

Case-control study

Recall biasBlind subjects to research hypothesis

Meta-analysis Publication biasLook for unpublished data

Confounds

A confound is a variable that is distributed differently in the study group and the control group and that affects the outcome being assessed. (Riegelman, 2005)

Confounding variables can appear through bias or random chance.

Probability

Probability is the quantitative estimate of the likelihood of condition existing (as in a diagnosis) or of subsequent events (such as in a treatment study). (Guyatt, Rennie, 2002)

P-value

P-value is the probability of an outcome occurring by chance. The p-value establishes statistical significance.

In medical research the standard p-value is p<.05

Power

Power is the ability of a research study to demonstrate statistical significance.

Researchers determine the size of study population needed for a set amount of power before beginning their study.

If the study has statistically significant results, the study has enough power.

In medical research the standard for power is 80%.

Readings:

Guyatt, G., Rennie, D. (Eds.). (2002). Users’ guide to the medical literature: a manual for evidence-based practice. USA: American Medical Association.

Katzer, J., Cook, K.H., Crouch, W.W. (1998). Evaluating information: a guide for users of social science research. Massachusetts: McGraw Hill.

Riegelman, R.K. (2005). Studying a study & testing a test: how to read the medical evidence. Philadelphia, PA: Lippincott Williams & Wilkins.