Case Study

Explain the research methodology concern raised by the colleague in this case. In your explanation, specify the type of validity in question and why the study's design makes generalization uncertain.

Case context: A clinical researcher conducts a single-subject study demonstrating that a new behavioral intervention successfully reduces self-injury in two children (n=2n = 2) who have intellectual disabilities. A practitioner at a school reads this study and wants to implement the treatment program-wide, but a colleague raises concerns about whether they can expect this treatment to be effective for the rest of the school's students who have similar delays.

Question: Explain the research methodology concern raised by the colleague in this case. In your explanation, specify the type of validity in question and why the study's design makes generalization uncertain.

Sample answer: The colleague is questioning the study's external validity (or generalizability). In single-subject research, because the treatment was only shown to be effective in a couple of children (n=2n = 2), it is unclear whether these positive effects will generalize to other children with similar intellectual delays in the broader school population.

Key points:

  • Identifies the threat to validity as external validity or generalizability.
  • Explains that success in a couple of children (n=2n = 2) does not automatically translate to the broader population.
  • Relates the concern back to children with similar intellectual delays in the broader population.

Rubric: The answer should clearly identify the issue as one of external validity or generalization. The student must explain that because the study used a single-subject design with only two children, there is insufficient evidence to guarantee the treatment will work for the wider population of children with similar delays.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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