Contemporary study (depression option): Hans and Hiller (2013)

Aims and method

Aims: to find the overall effectiveness of, and drop-out from, individual and group outpatient CBT for adults with a primary diagnosis of unipolar depression, in routine clinical practice.

Method: a meta-analysis of 34 effectiveness studies: non-randomised trials in ordinary clinical settings. RCTs were deliberately excluded, so the results reflect routine practice.

• Databases searched: MEDLINE, PsycINFO and PSYNDEXplus, plus reference lists.
• Included: face-to-face CBT for major depressive, minor depressive or dysthymic disorder. Excluded: studies with fewer than half of the usual 12 sessions, and narrow populations such as the elderly.
• Drop-out was defined as stopping treatment after attending at least one session.
• Hans coded every study; Hiller coded a random 20% to check inter-rater reliability, and disagreements were resolved by discussion.
• Results were benchmarked against RCT findings.

Results and conclusions

• Outpatient CBT produced substantial reductions in depression, and benefits appeared to last at least 6 months after therapy.
• Completers improved significantly more than those who dropped out.
• Individual and group CBT did not differ significantly in outcome.
• Drop-out was higher for individual than for group CBT; individual CBT drop-out was higher than the RCT benchmark.
• Roughly every fourth patient dropped out.
• The methodological quality of effectiveness studies was often poor.

Evaluation

• High ecological validity: routine practice, not ideal research conditions.
• Large combined sample across 34 studies increases generalisability.
• Inter-rater check on coding improves reliability.
• Lower internal validity: without randomisation or control groups, improvement could be due to time or other factors.
• Varying quality and definitions across studies (for example of drop-out) make combining them less precise.
• Supports Beck's theory and the use of CBT (8.1.7).

Worked example

Explain why Hans and Hiller excluded RCTs, and one consequence of this.

1. They wanted to know how CBT works in everyday clinical practice, not under ideal research conditions.
2. RCTs use selected patients and specially trained therapists, so they may overestimate effectiveness.
3. Consequence: higher ecological validity, but without random allocation and controls it is harder to be sure CBT caused the improvement (lower internal validity).

Answer: Excluding RCTs increased real-world validity but reduced control.

Check yourself

1. How many effectiveness studies were included in Hans and Hiller's meta-analysis?
   Show answer

   34. 34 studies.

2. Hiller coded 20% of the 34 studies to check inter-rater reliability. About how many studies is that? Give your answer to 1 decimal place.
   Show answer

   6.8. 0.20 x 34 = 6.8, so about 7 studies.

3. Which statement about Hans and Hiller (2013) is correct?
   • It was a single RCT
   • It only included group CBT
   • It studied children
   • RCTs were excluded so the findings reflect routine practice
   Show answer

   RCTs were excluded so the findings reflect routine practice. A common exam error was saying it used RCTs.

4. How was drop-out defined?
   • Stopping treatment after attending at least one session
   • Never attending any session
   • Finishing all sessions
   • Refusing to take medication
   Show answer

   Stopping treatment after attending at least one session. At least one session attended, then stopping.

5. Which finding did Hans and Hiller report?
   • Group CBT was much less effective than individual CBT
   • No patients dropped out
   • Drop-out was higher for individual than for group CBT
   • CBT had no effect
   Show answer

   Drop-out was higher for individual than for group CBT. Outcomes were similar, but individual CBT had more drop-out.

6. If roughly one in four patients drops out, how many of 200 patients starting CBT would be expected to drop out?
   Show answer

   50 patients. 200 / 4 = 50.

7. Explain one strength of Hans and Hiller's use of effectiveness studies rather than RCTs.
   Show answer

   Effectiveness studies take place in routine clinical practice with ordinary patients and therapists, so the findings have high ecological validity and generalise to real treatment settings.. Real-world settings give ecological validity.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification (issue January 2026)
• Pearson IAL Psychology component guide: WPS04 (Issue 2, November 2024)
• Pearson IAL Psychology summary of studies: WPS04
• Pearson WPS04/01 examiners' report, June 2025

Last updated 8 November 2026. Spotted a mistake? Tell us.