Helen Macdonald and Carl Heneghan are back again talking about what's happened in the world of evidence this month.

They start by talking about how difficult a task it is to find evidence that's definitely practice changing, what GPs can learn from Malawian children with nonsevere fast-breathing pneumonia, how radiation dosage varies substantially - and consultant radiologist Amy Davies what that means for patients.

They also rail against add-on tests for fertility, and the lack of evidence underpinning their use - will the traffic light system suggested help patients make treatment choices.

Carl's rant this week is based on a new study by Steve Woloshin and Lisa Schwartz which documented 20 years of medical marketing in the USA.

Reading list:

Pneumonia in Malawi - https://www.ncbi.nlm.nih.gov/pubmed/30419120

Variation in radiation dose - https://www.bmj.com/content/364/bmj.k4931

Traffic light fertility tests - https://www.bmj.com/content/364/bmj.l226