Lawyers working in small firms undertook more pro bono hours than colleagues in medium-sized practices, according to a new data index.

The TrustLaw Index, published by the Thomson Reuters Foundation, shows that lawyers at offices with fewer than 20 staff worked an average of 22.3 hours pro bono. Lawyers at firms with 20-99 fee-earners performed 19.3 hours pro bono.

However lawyers at firms with more than 100 fee-earners did 34.1 hours pro bono.

The index is based on data from more than 140 firms, representing 49,000 lawyers in 77 countries.

Lawyers at a firm with a formal pro bono policy performed 36.7 hours compared to 21.1 hours at firms that did not have a policy.

Firms with a pro bono requirement in place to encourage or require lawyers to do a minimum number of hours did more pro bono work on average (42.7%) than those without a requirement (29.3%).

Lawyers at firms where pro bono was factored into their appraisal performed 35.9 hours of pro bono work compared to 23.3 hours at firms where it was not taken into account.

In the UK, the number of pro bono hours performed by partners rose by almost 10% from last year to 14.9 hours in 2015.

Fee-earners performed an average of 21.9 hours compared to 21.3 hours last year.

The percentage of fee-earners that performed 10 or more hours pro bono fell slightly – from 36.1% in 2014 to 35.3% this year.

The percentage of partners who recorded time on pro bono matters also dipped – from 38.1% in 2014 to 37.8% this year.

Thomson Reuters Foundation chief executive and TrustLaw founder Monique Villa said having good data on pro bono was crucial.

‘It allows us to better understand where the industry is going, to set important benchmarks and to build up support for the practice.

Villa said last year’s index helped prompt the inception of the Collaborative Plan for Pro Bono, ‘with some of the country’s best law firms setting their benchmark at 25 hours of pro bono work per lawyer’.