A difference is not yet a treatment effect

A difference is not yet a treatment effect

Psychology studies behavior and mental processes through systematic evidence. Random assignment helps make treatment groups comparable; random sampling concerns who the sample represents. Blinding and consistent measurement address different sources of bias.

Inspect the case

Teaching study: volunteers choose a memory app or no app. App users recall 8 of 10 words on average; others recall 6.

Teaching recruitment notes: app users already practiced word games and chose harder classes. No random assignment occurred.

Both records are original fictional teaching materials. They are not historical primary sources and do not report real participants.

Work through the mechanism

The two-word difference is observed. Prior practice may explain part or all of it, so the app’s causal effect is not isolated.

Your investigation

Draw a comparison separating selection, treatment and outcome. Redesign the study with random assignment and a consistent outcome test.

Make a two-column evidence table: what the record directly supports, and what you infer. Use record IDs when connecting observations to claims. Preserve your first interpretation before revising it.

Practice and transfer

What does random assignment mainly improve?

Try the practice check in the activity, explain your choice, then apply the idea to this unfamiliar case: A randomly assigned study uses only one school’s volunteers. What remains limited?

Limits and responsible interpretation

This is a study critique, not an invitation to experiment on classmates. Supplied records avoid consent and privacy risks.

A successful answer identifies a mechanism and its boundaries. A saved response records practice; it does not automatically establish independent understanding.

Further reading

OpenStax: Psychology 2e provides disciplinary context. The teaching records above were authored for this lesson and are not quotations from that source.

Choose your depth

High school: Use the supplied records to complete this task: Draw a comparison separating selection, treatment and outcome. Redesign the study with random assignment and a consistent outcome test. Explain your reasoning in a short paragraph or an annotated diagram with a text equivalent.

AP connection: Build an original stimulus-based response: identify the relevant Psychology concept, cite a specific detail in each record and explain a limitation. Then answer the transfer question without reopening the worked example. This is practice, not an official AP question.

Introductory college: Frame a researchable version of the case, document definitions and source selection, and compare the supplied mechanism with a rival explanation. Use the linked disciplinary reading to find one relevant scholarly or institutional source; distinguish that real source from these fictional records. Submit a revision log and methods note.