| Ref ID | 468 |
| First Author | B. Tendal |
| Journal | BMJ |
| Year Of Publishing | 2011 |
| URL | https://www.bmj.com/content/bmj/343/bmj.d4829.full.pdf |
| Keywords |
• General medical • Cochrane • Multiplicity |
| Problem(s) |
• Weaknesses identified in some Cochrane reviews • Multiplicity of outcomes and lack of pre-specification for outcome reporting |
| Article Type | Empirical |
| Article Subtype | Meta-epidemiological analysis |
| First Author Country | Denmark |
| Aim | To assess the extent of multiplicity of data in trial reports and to assess the impact of multiplicity on meta-analysis results of a sample of Cochrane systematic reviews published 2006 to 2007. Reviews with protocols and meta-analyses that presented data with a standardised mean difference were included. |
| Level of Investigation | Analytical |
| Summary of Findings | Review protocols often lacked information about which data to choose. There was multiplicity of data in at least one trial report. 29% trials reported data for multiple intervention groups, 36% reported data for multiple time points, and 35% reported the index outcome measured on multiple scales. The impact of multiple data in trial reports regarding intervention groups, time points, or measurement scales on meta-analysis results varied greatly across meta-analyses, ranging from almost no effect (0.04 standard deviation units) to a substantial one (0.91 standard deviation) units, corresponding to a large treatment effect. |
| Number of systematic reviews included | 19 |
| Number of eligible systematic reviews assessed | 32 |