How to read a forest plot

Researchers undertook a meta-analysis of the safety and efficacy of antibiotic treatment compared with appendicectomy for the primary treatment of uncomplicated acute appendicitis. Randomised controlled trials were included if they investigated adult patients presenting with uncomplicated acute appendicitis, diagnosed by haematological and radiological investigations. The primary outcome measure was the presence of complications, including wound infection, perforated appendicitis, or peritonitis. Four randomised controlled trials were identified.1 The results of the meta-analysis for complications were presented in a forest plot.⇓

Which of the following statements, if any, are true?

• a) Not one of the four trials showed a significant difference between antibiotic treatment and appendicectomy in the risk of complications.

• b) The forest plot is drawn on a linear scale.

• c) A relative risk less than 1.0 represents a reduced risk of complications for antibiotic treatment compared with appendicectomy.

• d) The meta-analysis of complications showed a relative risk reduction of 31% for antibiotic treatment compared with appendicectomy.

• e) No significant heterogeneity existed between the sample estimates of the population relative risk.