| Ref ID | 245 |
| First Author | C. J. Oliver |
| Journal | BMC COMPLEMENTARY & ALTERNATIVE MEDICINE |
| Year Of Publishing | 2017 |
| URL | https://bmccomplementmedtherapies.biomedcentral.com/track/pdf/10.1186/s12906-017-1906-x.pdf |
| Keywords |
• Vitamins and supplements • External validity • Cochrane |
| Problem(s) |
• Weaknesses identified in some Cochrane reviews • Overly stringent inclusion criteria affecting external validity • Inflexible methods to complex questions |
| Article Type | Empirical |
| Article Subtype | Case study |
| First Author Country | Australia |
| Aim | To assess a Cochrane Database Systematic Review published in 2012 which concluded that α-tocopherol forms of vitamin E have a statistically significant effect on mortality, by assessing the trials and datasets used and determining their effect upon the primary outcome |
| Level of Investigation | Descriptive |
| Summary of Findings | An analysis of one Cochrane Systematic Review published in 2012 which concluded that α-tocopherol forms of vitamin E found a 3 cell analytical method comparing all vitamin E cells (vitamin E alone plus vitamin E + β-carotene) to the placebo only cell. This meta-analysis had the unfortunate effect of incorrectly inflating the mortality risk attributed to vitamin E by not balancing the contribution to mortality of the β-carotene intervention. Studies with low numbers of events, i.e. low mortality rates, had little or no impact on the analysis and resulted in a high weighting on the ABTC study from A11. Re-analysis of the ATBC trial using data derived from the more generally accepted ‘inside the table’ (2 cell – vitamin E versus placebo) or ‘at the margins’ (4 cell – all vitamin E versus all non-vitamin E) analytical methods demonstrates a statistically non-significant result. The authors state that current meta-analysis methods do not allow for studies with low (or no) mortality to be incorporated in a meaningful way. |
| Number of systematic reviews included | 1 |
| Number of eligible systematic reviews assessed | 1 |
| Treatment impacted | Yes |
| Treatment impacted description | Re-analysis of the ATBC trial using data derived from the more generally accepted ‘inside the table’ (2 cell – vitamin E versus placebo) or ‘at the margins’ (4 cell – all vitamin E versus all non-vitamin E) analytical methods demonstrates a statistically non-significant result. |
| Interpretation impacted | Yes |
| Interpretation impacted description | Using the 3 cell analysis method only the 6 and 8-year (used in the meta-analysis) follow-up periods were statistically significant. Using the 2 or 4 cell method the outcome remains non-significant over all time periods. |