Muslim Population Growth: Sex Ratio & Rural Populations

The common refrain of many when Census data showed high Muslim growth rates was: look at Kerala. Let’s look.

Two factors that were reported by the Census data and pointed to as factors that could, at least in part, explain the higher growth rates of Muslims were: sex ratio and percentage of rural population. It’s a reasonable hypothesis. After all, fewer women mean fewer women who can bear children and vice-versa. Similarly, a greater percentage of rural population means more people with lower socio-economic status pointing to higher fertility rates. But is that hypothesis, while well founded in literature[1], hold up within the data set[2] released?

The first thing one does when told one variable may be predicting another is to simply plot the data, before any analysis. A plot of rural population in various states as X and Muslim growth rates in population as Y looks thus.



A similar plot against sex ratio is,


There really is nothing discernible to the naked eye from these scatter plots. If anything, it appears more women correlates to lower growth rates. Not higher.

The next thing we’d do is simple linear regression. There seems to be no linear relationship between rural population and growth rates for Muslims. There isn’t an exponential relation either. But the data for sex ratio among Muslims is a tiny bit more interesting. At least within this flawed model which predicts nothing, if at all there is a wager it’s that more women seems to point to lower rates of growth. 

It’s useful in such cases to just see the two variables interact on a response surface. For this purpose, let’s model this as a Gaussian Process[3].



As we’d expected, the response surface doesn’t move much except for the places X2 acts up. X1 is rural population and X2 is female population as a percentage. The basic point of the data that Muslims have higher growth rate is captured well, though. To understand that even better, let’s look at how the corresponding response surface for Hindus looks,

HinduGPAgain, there is no evidence for rural populations outpacing their urban peers, much. But female population seems to suggest a concentration in the middle and a plunge when the ratio of women increases. The scatter plot of Hindu women and their population growth is in this direction as well,


Of course we know from living in the real world that more women are not resulting in lower population growth. The reason is likely to be the reverse: socially advanced states have better sex ratios and low fertility rates, resulting in low growth.

With the data that’s been released by Census, there isn’t a conclusive model for anyone to conclude reasons within this set. There isn’t even a bad model. But we at least know the hypothesis that lower IMR and hence better sex ratio is a contributing factor to high Muslim growth rates has no evidence. Rural population ratios don’t seem to matter, either.

[1] – Demography as a Science is far too advanced for lay people to just make stray observations. When searching for the model Demographers use to estimate human population, I found this thesis; it’s quite useful as background reading material. Hopefully, I’ll understand the models better in the near future.

[2] – Data used here is the from the same source as the previous post: Census of India.

[3] – Please do not take this to mean anything more than an illustration of the variable’s effects. The GP here is not a real model given how limited the data is. And don’t blame me if you get a failing grade for doing this in class.

[4] The Model details, if you are interested in wrong models that is, of the two GPs.