Cochrane

# Supplementary material 9 to:
Interventions for preventing falls in older people living in the community

Gillespie LD , Robertson MC , Gillespie WJ , Sherrington C , Gates S , Clemson L , Lamb SE
https://doi.org/10.1002/14651858.CD007146.pub3

Cochrane disclaims all liability and responsibility arising from any reliance placed on this supplementary material which has been supplied by the author(s). The above associated publication’s Author Licence will apply in respect of any supplemental materials published. How to cite the supplementary material is defined in the Cochrane policy.

# 'Risk of bias' assessment methods for incomplete outcome data (attrition bias)

## Falls

For studies reporting falls as an outcome, we first calculated a rate ratio (RaR1) by dividing falls per person year in the intervention group by falls per person year in the control group. If these data or the numbers lost to follow-up in each group were not available we assessed the risk of bias as 'Unclear'. We estimated a second rate of falling for all participants randomised (RaR2) by using the conservative assumption that participants lost to follow-up in the intervention group had the same rate of falls as observed in the control group, and vice versa.

A ratio of these rate ratios (RaR2/RaR1) of greater than 1.15 or less than 0.85 was assessed as 'High risk' indicating the possibility of clinically important bias; studies with values between 0.85 and 1.15 were assessed as 'Low risk'.

## Fallers

For risk of falling, we first calculated for intervention and control groups in each study a risk of falling and a risk of falling ratio (RR1) using for each group the number of participants falling divided by the number analysed. Where the number analysed in each group was not provided, we used as denominator the number in each group providing complete data on falling throughout the study period. Where these data were not specifically mentioned, we used number of participants randomised less the number lost to follow-up as the denominator.

Using the conservative assumption that participants lost to follow-up in the intervention group had experienced the risk of falling observed in the control group, and vice-versa, we calculated an estimated risk of falling ratio for all participants randomised (RR2). We added an imputed number of fallers in each group (the number of lost participants who might have experienced a fall) to the observed number of fallers in each group. The number randomised to that group was used as the denominator.

A ratio of the risk ratios RR2/RR1 of greater than 1.15 or less than 0.85 was assessed as 'High risk' indicating the possibility of clinically important bias; values between 0.85 and 1.15 were assessed as 'Low risk'. When data were not available to calculate RR1 and RR2, risk was assessed as 'Unclear'.