Akshay Kumar stars as a policeman in a set of viral videos endorsing road safety. Amitabh Bachchan endorses Tata Sky, Dabur, Navratan Oil, Dairy Milk... and also TB, Polio and Nutrition.

Using celebrities to persuade is a time honoured tactic – both in the private and social sector. 24 per cent of commercials aired in India are celebrity endorsed, lower than Japan (70 per cent) but higher than Europe (<15 per cent). And yet, there is surprisingly little research in India on the role of celebrities in persuasion.

At the Centre for Social and Behaviour Change, one of our aims is to undertake research that helps craft more effective behaviour change interventions for poor and marginalised communities. So, with the Yale Centre for Customer Insights, we set out to answer the question of how and when to effectively use celebrities to motivate social and behaviour change. We scanned peer-reviewed literature in a variety of subjects, ranging across disciplines. This included social psychology, behavioural economics and marketing, and general business literature.

Celebrities work – athlete endorsements were associated with a 4 per cent increase in sales for a sample of consumer goods companies and a 0.25 per cent in stock return on the day of announcement. They were associated with a small but consistently higher donation contribution – 1.5 per cent over control. To put this number in perspective, a recent study showed that the wealthiest Indians donated 1.6 per cent of their net household income to charity.

When are celebrities most likely to be effective? Celebrities can add extra persuasion power when people are likely to be resistant to messaging e.g. in the health or political sector. They can also be effective when people desire an aspirational image and can be used to upgrade many health or charity behaviours.

Importantly, when people are mentally depleted and not paying attention, celebrities can help cut through the clutter. What makes for a good celebrity endorser? Research suggests a good endorser has three characteristics: s/ he is likable, credible, and relevant (matches audience characteristics).

Likeability is a combination of several factors: sheer attractiveness, familiarity, authenticity and interest the celebrity shows in the cause or brand. Likeability leads to persuasion because, as human beings, we fall prey to the “halo effect” – and judge people we like as consistently more intelligent and trustworthy. Further, through a simple conditioning effect, celebrities transfer positive associations to the brand. It is therefore critical to pick a liked celebrity.

Likability is not enough – the celebrity also needs to be viewed as credible in the category. In a lab study, simply manipulating the person’s identity (Olympic athlete vs. actor) changed people’s intent to purchase endorsed products. Specifically, when the “celebrity” was framed as an actor, 61 per cent indicated they would buy an energy bar endorsed by him but when the “celebrity” was framed as an Olympic athlete this increased to 65 per cent. Credibility is a result of perceived expertise in the category, trustworthiness and altruistic motivations. Julia Roberts and Angelina Jolie may be equally liked as celebrities, but Angelina Jolie may be viewed as more credible around saving orphans from Darfur.

Finally, and this is often overlooked, celebrities are most effective when they are personally relevant. The audience is more likely to be persuaded by someone whose age or gender matches theirs. In a lab study, Gen X participants were more likely to purchase an endorsed product when Madhuri Dixit was endorsing it vs. Deepika Padukone. However, for Gen Y it was the reverse.

One of the surprising things that emerged from our literature review was the lack of evidence in India around celebrity endorsement. In keeping with our vision to create an institution in India we plan to address this by A/B testing some of these findings using Indian celebrities. For example, what is the relative value of attractiveness vs. matching? Is there a dilution effect (important in India, given the multiple brands and services celebrities endorse)? Stay tuned for the second phase of this work!