Placebo-adjusted effect: difference between revisions
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| 10 | The active-arm change alone conflates the treatment effect with everything else operating during the trial: regression to the mean, the natural course of the condition, the lifestyle intervention both arms received, and the effects of being observed.{{r|hrobjartsson2010}} | 10 | The active-arm change alone conflates the treatment effect with everything else operating during the trial: regression to the mean, the natural course of the condition, the lifestyle intervention both arms received, and the effects of being observed.{{r|hrobjartsson2010}} |
| 11 | 11 | ||
| + | 12 | In obesity trials the distinction is substantial. [[STEP trial programme|STEP 1]] reported −14.9% on semaglutide and −2.4% on placebo, so the placebo-adjusted effect is about 12.4 percentage points — not 14.9.{{r|wilding2021}} | |
| + | 13 | ||
| 12 | == What the comparator arm captures == | 14 | == What the comparator arm captures == |
| 13 | A placebo arm in a modern obesity trial is not a no-treatment arm. Participants receive the same lifestyle counselling, the same visit schedule and the same measurement, and the difference between the arms is the treatment alone.{{r|hrobjartsson2010,ich_e10}} | 15 | A placebo arm in a modern obesity trial is not a no-treatment arm. Participants receive the same lifestyle counselling, the same visit schedule and the same measurement, and the difference between the arms is the treatment alone.{{r|hrobjartsson2010,ich_e10}} |
| ⋮ | ⋮ | ||
| 15 | Several distinct phenomena contribute to the change in a placebo arm. Regression to the mean operates because participants are enrolled at a moment when their measurement was high enough to qualify. The trial's own intervention — diet advice, activity advice, regular weighing — has an effect. Observation changes behaviour. And the natural course of a condition may be towards improvement or deterioration.{{r|hrobjartsson2010}} | 17 | Several distinct phenomena contribute to the change in a placebo arm. Regression to the mean operates because participants are enrolled at a moment when their measurement was high enough to qualify. The trial's own intervention — diet advice, activity advice, regular weighing — has an effect. Observation changes behaviour. And the natural course of a condition may be towards improvement or deterioration.{{r|hrobjartsson2010}} |
| 16 | 18 | ||
| + | 19 | The placebo response proper — improvement attributable to expectation — is only one of these, and in objective endpoints such as body weight it is generally small relative to the others.{{r|hrobjartsson2010}} | |
| + | 20 | ||
| 17 | == References == | 21 | == References == |
| 18 | {{reflist}} | 22 | {{reflist}} |
| 19 | <ref name="ich_e9">International Council for Harmonisation, ''E9(R1): Estimands and Sensitivity Analysis in Clinical Trials'' (2019).</ref> | 23 | <ref name="ich_e9">International Council for Harmonisation, ''E9(R1): Estimands and Sensitivity Analysis in Clinical Trials'' (2019).</ref> |
| 20 | <ref name="hrobjartsson2010">Hróbjartsson A, Gøtzsche PC. "Placebo interventions for all clinical conditions." ''Cochrane Database of Systematic Reviews'' (1):CD003974 (2010). PMID 20091554.</ref> | 24 | <ref name="hrobjartsson2010">Hróbjartsson A, Gøtzsche PC. "Placebo interventions for all clinical conditions." ''Cochrane Database of Systematic Reviews'' (1):CD003974 (2010). PMID 20091554.</ref> |
| + | 25 | <ref name="wilding2021">Wilding JPH, Batterham RL, Calanna S, et al. "Once-weekly semaglutide in adults with overweight or obesity." ''New England Journal of Medicine'' 384(11):989–1002 (2021). PMID 33567185.</ref> | |
| 21 | <ref name="ich_e10">International Council for Harmonisation, ''E10: Choice of Control Group and Related Issues in Clinical Trials'' (2000).</ref> | 26 | <ref name="ich_e10">International Council for Harmonisation, ''E10: Choice of Control Group and Related Issues in Clinical Trials'' (2000).</ref> |
| 22 | 27 | ||
| ⋮ | ⋮ | ||
| 24 | [[Category:Research methodology]] | 29 | [[Category:Research methodology]] |
| 25 | [[Category:Evidence appraisal]] | 30 | [[Category:Evidence appraisal]] |
| + | 31 | [[Category:Clinical evidence]] | |
| 26 | 32 |