I & Birthdates

One fine morning, I land on the my Orkut page and suddenly the section of upcoming birthdays which had just 1 row a few days back had 4 rows. That is a dramatic increase. That was mid-August and the number of rows of upcoming birthdays has stayed constant at 3 since then now. I suppose the trend is about to stay.

That prompted my curiousity and I asked myself, if indeed people are more likely to be born in few months of the year? And if so why? I had a hypothesis for the why. But to prove it no data. So, the trained manager that I am, I put my skills to use and did this: Start > Programs > Google Chrome > Google Chrome > Alt + D > distribution of birthdays across months > Enter. Actually, I have a shortcut for Chrome (Ctrl + Alt + G, I am really hooked on to this browser), but the former method has some hint of sophistication.

Rest assured, Google always has the answer - actually 30,900,000 answers. And in this case, I found my answer at Google Answers. It led to this page - An Analysis of Distribution of Birthdays in a Calendar Year. This guy had actually taken over 400,000 birth date data points (all United States) and plotted their distribution, by day-month, by month and by day of month. He conducted chi-square test of fit of a distribution to check if it is uniformly distributed and found that it is not.

Birthdays were higher than expected from July to October while for rest of month it was lower than expected (significantly or insignificantly). Of course, a logical conclusion is that October (July - 9 months) to January (October - 9 months) where 9 months is the average period of pregnancy, is somehow a suitable time period for conception. Now in US, figuring the equation out might be pretty simple, especially, where the North Hemispherean winter is harsh and people are forced to stay indoors most of the time in that period. Also, in the holiday season, they stop relaying new TV shows. So, you really have nothing but one thing to do. Should I name it? In the interest of keeping this post clean and avoid the risk that some "ist" might report abuse of this blog, I will not, but I guess everyone must have figured what I am talking about by now. If not, I really sympathise with you.

However, this might not be an explanation applicable to all. Now, somebody in hot Texas or the humid California and Florida does not really have to worry too much about the winter. It may as well be true that the distribution of birthdays is uniform in such temperatures. But winter may not be the only reason that could account for this distribution. It is known fact that high temperature environments are ill-conducive to generation of the agents of change (to put it unabusively). Besides, it would be difficult to play baseball when one is perspiring. Baseball is a game very much like cricket. Except that they don't have stumps, their bat is a mini club, they call a six as a home run... Wait a minute, I wasn't writing about baseball. Hmm... where was I? So, even in Texas, 9 months from the lowest temperature period of the year, the North hemispherean winter, would most likely account for more births than other months. Thus, there could be physiological and lifestyle reasons for the observed distribution.

Wait another minute, I do not have a single dumb friend. Then why am I studying US data. What waste!

And so, I browsed through the results to look for Indian data. I clicked a link which led to another and I found this: Seasonality of Births and Possible Factors Influencing it in a Rural Area of Haryana, India. This study of 35,328 births between 1972-90 show that there is almost a sinusoidal frequency curve with a clear trough and clear peak. And the peak was spread over July to November. Actually this study includes a discussion on factors too. They discuss the following:

1. Seasonality of weddings (and hence first wedding nights) coupled with lack of contraception in rural India (in that time period). But I don't buy this. Most auspicious dates for wedding start from mid-March to early-June. I know because of the hordes of wedding invitation cards, my parents receive each year in that period while receiving scanty invitations rest of the year.
2. Next factor, they figure is winter. Taken.
2a. Combined with lack of privacy, however, winter, they say, should have adverse effect.
2b. Availability of leisure time due to slackness in agricultural work.

And then they list this set of "potentiating" and "inhibiting" factors. Potentiating: holidays/festivals, conducive weather, agricultural cycle, seasonality of marriage, use of contraception. Inhibiting: air conditioning of homes, contraception, religious proscription, food availability.

But these are for rural India and with almost 19 year old data in rural Haryana. Now, most of my friends actually hail from cities and as far as I know, most of them weren't born in rural Haryana. Unfortunately, there is no study about seasonality of births in urban India. Pulling data of Orkut is going to take years. So, I am commissioning a primary research to study seasonality of birth in urban India. I request you to cooperate with me and help me in this quest. Please fill this form (click here). I promise you that you will get nothing but my sincere gratitude in return of your debt. Savvy investment bankers can make a CDO or a CDS or any other funky named instrument out of it and make money. Anyway, once there is enough data, I will post the summary data.