Did use of helmets reduce deaths due to 2 wheeler accidents?

This blog post is about the analysis of implementation of helmet rule in various Indian states and the effect it had on bringing down accidental deaths due to 2 wheelers. Here we are specifically focussing on one particular state, Karnataka.
National Mandatory helmet legislation is included in the Indian Motor Vehicles Act, 1988.  However, implementing this law has been left to the individual states. Karnataka gov. enforced mandatory helmet rule for all 2 wheeler riders in the year 2007. Traffic cops started imposing fines to violators of the rule and within no time, good compliance to the rule was observed. Accidental Deaths & Suicides in India publicizes the data about accidental deaths broken down by type of vehicle and by state (from 1967 to 2009). Considering the state of Karnataka, looking at the accidental deaths due to 2 wheelers and plotting the trend we see a clear decline in accidental deaths after 2007, specifically 8% decline in accidental deaths as of 2009. But can we just attribute this drop in accidental deaths to the helmet rule? Let’s explore.