Six Degrees of Kevin Bacon is a game in which movie buffs challenge each other to find the shortest path between an arbitrary Hollywood actor and the well-known character actor Kevin Bacon, using films in which both have starred. The standing joke is that this can always be done in six steps or fewer.
Back in 2008, a group of researchers at the University of Maryland tested this idea by constructing a network of links between Hollywood actors using data from the Internet Movie Database. To everyone’s surprise, they found that the best-connected actor was not Kevin Bacon but William Hurt, a piece of information that will no doubt be hugely useful in trivia quizzes of the future.
Since then, the study of social networks has exploded. But while researchers have used Hollywood actors as an interesting case, they have ignored the largest acting network entirely.
The Indian film industry, sometimes called Bollywood, is the world’s largest producer of films and dwarfs its American counterpart. In 2009 alone it produced almost 3,000 films, and the industry itself both reflects Indian culture and has a profound influence on it. That makes it an interesting subject for analysis.
Today we get just such a study thanks to Sarika Jalan at the Indian Institute of Technology Indore in India and a few pals. These guys have mined several databases of Indian films from the last 100 years to create a comprehensive network showing male and female actors who have worked together on the same film.
And their network provides some fascinating insight into the nature of the Indian film industry and its links to broader Indian culture as well. It shows not only how combinations of actors have been particularly successful but also how the industry has waxed and waned in response to the broader economic and social conditions in the country at large.
Jalan and co begin by analyzing the cast lists from almost 9,000 movies made in Bollywood between 1913 and 2012. Each actor is a node in this network, and a link is drawn between them if they both acted in the same movie. By dividing the hundred-year time span into five-year blocks, Jalan and co can see how this network has evolved over time.
This network is similar in many ways to other social networks. For example, the number of links per node, known as their degree, follows a power law. In other words, a small number of actors have a very large number of links, or a high degree, while a large number of actors have a low degree.
That raises an interesting question: are the best-known and most successful actors also the best-connected individuals in the network? To find out, Jalan and co manually compiled a list of leading male and female actors, chosen according to their billing (whether the lead or not) and the number of significant awards they had received.
To their surprise, they found that leading actors are not the best-connected. “The most important nodes of the industry, acknowledged as the lead male actors, do not form the hubs of the constructed network, but instead have a moderate degree,” they say.
Instead, the best-connected actors turn out to be prominent supporting actors who can take on more projects in a given time period and therefore end up collaborating with a larger number of other actors. That’s similar to the Hollywood network, where prominent supporting actors such as William Hurt and Kevin Bacon are also better connected than superstars such as Tom Cruise and George Clooney.
The supporting actors are a kind of glue that knits the network together. This is reflected in a parameter called betweenness centrality, which measures how likely it is that a node sits on the shortest path between one part of the network and another.
Female actors are nowhere near as prominent in this network as men. Jalal and co say this gender gap reflects a similar disparity in Indian society as a whole.
Perhaps the most interesting aspect of this work is the way the Bollywood network has changed over time. In particular, Jalal and co have studied the underlying randomness in the network and how it has changed.
They say that the network has become less random, with a couple of notable exceptions. Between 1948 and 1952, the network became more random, probably because of the significant upheaval associated with partition when the country split in two. Another period of increasing randomness occurred between 1962 and 1965, during the period of economic crisis when India was at war with Pakistan.
Interestingly, the network also changed dramatically after 1998, when it grew rapidly and became more interconnected. This is probably the result of Bollywood becoming a globally recognized phenomenon rather than just a national one.
One question that comes to mind is whether these network studies reveal the greatest Bollywood actor in history. Jalal and co refrain from making too much of this, but their data point to Amitabh Bachchan, who tops a number of lists in terms of significance.
The most significant female actor is less clear, although Kareena Kapoor and Helen get special mentions.
That’s fascinating work providing an insight into one of the world’s great industries.
Ref: arxiv.org/abs/1406.4607 : Uncovering Randomness and Success in Society