This free access 2014 article in BREATHE unpacks what goes into Systematic reviews and gives pointers about how to appraise them. We use an example of the Cochrane systematic review comparing spacers with nebulisers to deliver salbutamol in acute asthma in adults and children.
Links
What is heterogeneity and is it important? (BMJ 2011)
There is no heterogeneity between steroids and antihistamines as I argue in my response to this BMJ article in 2011:
http://www.bmj.com/rapid-response/2011/11/01/there-no-heterogeneity-between-steroids-and-antihistamines