Meta-analyses: standardised mean differences

Researchers undertook a meta-analysis of the effects of local anaesthesia for pain control during hysteroscopy. Randomised controlled trials were included if they compared local anaesthesia with no intervention, placebo, oral analgesics, or conscious sedation. Participants were women undergoing diagnostic or operative hysteroscopy as outpatients without general anaesthesia. The primary outcome was pain associated with the procedure.1

In total, 15 trials were included. Four methods of administration of local anaesthesia were identified—intracervical, paracervical, and transcervical injections plus topical application. The trials used different scales to assess the pain associated with the procedure, including continuous visual analogue scales and numerical scales. The standardised mean difference in pain between treatment groups (local anaesthesia minus control) was derived for each trial. The results of the meta-analysis were presented in a forest plot, with those for the subgroup of paracervical injections shown (fig 1⇓).

Which of the following statements, if any, are true for the subgroup of paracervical injection of local anaesthesia?

• a) For each trial, the standard error of the mean difference was used to calculate the standardised mean difference

• b) For each trial, the standardised mean difference was on the same scale as the original measurement of pain

• c) The standardised mean differences allowed a direct comparison of treatment effects across …