Which type of evidence provides the best indication to try a new treatment?

• A. In a published study, many children similar to X are randomly assigned to receive B and show better outcomes than those randomly assigned to receive A.
• B. You take a course from a well-known expert who shows videos of how to implement B and you see many children similar to X making good progress with this approach.
• C. A local clinic adopts B as routine practice and reports better outcomes overall compared to the previous year when they were using A.
• D. Your friend, colleague and mentor reports that she recently tried B with a client similar to X and was very pleased with the outcome for her client.

Answer: (A)

Randomized controlled trials provide the strongest evidence because random assignment and a control group help isolate the effect of the new treatment from other factors. When many children similar to X are randomly assigned to receive B or A and the B group shows better outcomes, we can be more confident that the improvement is due to B rather than biases or external influences. Other sources—expert demonstrations without a control, before-after outcomes in a single clinic, or anecdotal reports—are more vulnerable to biases like placebo effects, confounding factors, or natural variation, so they don’t establish causality as reliably. This design therefore offers the best indication to try the new treatment.