International legal research company Acritas says research for its global Sharplegal study of senior in-house counsel found that male law firm clients were half as likely to nominate a female lawyer for its "Star" category than a male.

Acritas compiles the "Stars" database for its global panel of General Counsels.

"Only 15% of male-nominated Stars were women. This compared with 29% of female nominated Stars being women - almost twice the level," says Acritas CEO Lisa Hart Shepherd.

"The effect of this bias is multiplied when you consider four out of five senior in-house counsel are male, it is therefore easy to see why female partners find it hard to get equity partnerships in law firms."

Acritas says when it looked closely at the reasons behind selection, the data showed the quality of expertise was the number one star quality for both genders in equal measure.

"However, female Stars on average had a higher number of qualities mentioned in their nominations. Female Stars were significantly more recognized for being responsive, approachable, professional and diligent."

Acritas says that to help increase the levels of diversity at senior levels in law, it will campaign for more senior in-house counsel to work towards greater gender diversity by setting quotas at a minimum level of 1 in 3 female-led instructions.

“The gender gap at equity partner level will only see material change if clients use their buyer muscle to give female lawyers in private practice more power," Ms Shepherd says.

"Money still talks in law firms and those who bring in the business are the ones who rise to the top.”

The New Zealand Law Society and New Zealand Bar Association are managing the Gender Equitable Engagement and Instruction Policy which has the objective of policy adopters using reasonable endeavours to have women lawyers with relevant expertise take a lead on at least 30% of court proceedings, arbitral proceedings and major regulatory investigations.