In outcome testing, what is the difference between independent and dependent measures, with PT examples?

• A. Independent measures are measured by the patient; dependent measures by the therapist
• B. Independent variable is the treatment; dependent variable is the outcome measured (e.g., ROM, pain, function)
• C. Independent measures are not related to treatment; dependent measures are always objective
• D. Independent and dependent measures are interchangeable in PT studies

Answer: (B)

In outcome testing, you’re looking at what you change and what you observe as a result. The thing you manipulate is the independent variable — the treatment or intervention you apply. The thing you measure afterward is the dependent variable — the outcome that changes in response to the treatment. In physical therapy, common outcomes include range of motion, pain, and functional ability.

For example, if you’re comparing two different rehab approaches for a knee issue, the rehab approach itself is the independent variable. The outcomes you track—knee ROM in degrees, pain level on a scale, and a functional measure like a walk test—are the dependent variables, because they depend on which treatment the patient received.

Even in a study where you vary the dose or intensity of an exercise program, that dose is the independent variable, and the resulting changes in ROM, strength, gait speed, or functional scores are the dependent variables.

That’s why the other statements aren’t correct: the distinction isn’t about who measures the outcome, independent variables aren’t unrelated to treatment, dependent measures aren’t necessarily objective (pain scales are subjective but valid outcomes), and independent and dependent measures aren’t interchangeable.