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Open Access Highly Accessed Research article

The interpretation of systematic reviews with meta-analyses: an objective or subjective process?

Ian Shrier*, Jean-François Boivin, Robert W Platt, Russell J Steele, James M Brophy, Franco Carnevale, Mark J Eisenberg, Andrea Furlan, Ritsuko Kakuma, Mary Ellen Macdonald, Louise Pilote and Michel Rossignol

BMC Medical Informatics and Decision Making 2008, 8:19  doi:10.1186/1472-6947-8-19

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EBM mischaracterized

Eddy Lang   (2008-06-26 15:47)  McGill University email

Intriguing study but you've missed the boat on one of the 2 central tenets of EBM (the other relating to the hierarchy of evidence). What is important to remember is that evidence alone is never sufficient to drive decision-making and a consideration of context, values and preferences are crucial. It is no wonder then that only the cardiologists got the correct interpretation of the systematic reviews that were presented to them. Only they were able to appreciate that most of this research was done in an era when MIs were treated very differently and that the significant increase in hypotension and heart block that comes with magnesium is nothing to sneeze at.

The authors of this Cochrane also got it right by concluding that: Owing to the likelihood of publication bias and marked heterogeneity of treatment effects, it is essential that the findings are interpreted cautiously. From the evidence reviewed here, we consider that: (1) it is unlikely that magnesium is beneficial in reducing mortality both in patients treated early and in patients treated late, and in patients already receiving thrombolytic therapy". Seems clear enough to me.

Systematic reviews are however not immune to "spin" by those who write them (or interpret them) and that is why we try to teach our students to take author conclusions (or anyone else's take) with a grain of salt. Go straight to the data, consider the heterogeneity and then apply the evidence to your practice.

There's absolutely nothing wrong with two diametrically opposed courses of action if the values and preferences of the situation dictate different applications of the same evidence.

Cheers,

Competing interests

I coordinate the EBM undergradiate course at McGill University.

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