Hey! There’s a simple question for you at the end of this, don’t forget to scroll down and click to let your voice be heard!

Indians who have lived in either or both of Delhi and Mumbai will at some point make a comparison between the two cities and you’ll know why they have a strong preference for one over the other. Even expats in India who have lived in one and visited the other will express fairly strong opinions about one or both cities.

As a recreational distance runner, I am well aware of the claims that are made about the Airtel Delhi Half Marathon being a “faster race” than the Standard Chartered Mumbai Marathon. Both are held in the winter, with Mumbai scheduled for the third Sunday of January, and Delhi some weeks before that. In my life as a hedge fund manager, what mattered was not just how well you performed but also why your performance was the way it was – how much was from your effort or skill, and how much was just luck! Your time in a race will be a function of many things on race day, some that are to do with you, others that are to do with various features of the race itself.

The Question
The question I set about to answer was “how much faster is Delhi than Mumbai?”. Internationally, there are rating factors, a single number between 0-100 (or between 0-1) that rate races based on a given set of factors. However, I preferred to dig for a deeper understanding of Delhi vs Mumbai, the two most popular races in India. Would you like to know how much slower (or, perhaps, faster!) you will be in Mumbai than in Delhi? And how does that vary based on whether you are a 1:30 half marathoner as opposed to a 2:30 half marathoner?

Data & Methodology
Ideally, to make a comparison, you would like the weather and the course for both races to be the same every year – they are not. You would also like the same runners to participate in both races with the same level of fitness and race motivation. Often your motivation for one race is to “push hard” for the other it is to “do an easy pace”.

So, practically, I identify runners who ran both races a few weeks apart and thus am able to work with differences in race time for the same runner in both races. By using multiple race years and thousands of runners I hope to iron out any statistical variations and glean some useful information from the data.

Looking at the 6 races in Delhi from 2009 to 2014 I could identify 5,525 individual runners (by name, gender and age category) who ran both Delhi and Mumbai in any given season. From these records, obvious outliers were removed, many of them because it was clear that they ran the half marathon in Delhi but the full marathon in Mumbai a few weeks later.

Race Specific Backgrounds to Bear in Mind
There are features of the races that are specific to the comparison.
Time of Year
The Delhi race is earlier in the primary racing season, which for the main and older races in India happen between the end of the Monsoons and culminate with the race in Mumbai. Of course, fortunately, there are races in India all through the year now but the premium races are bunched in the period between October and January.
Weather
Delhi is colder in Nov-Jan than Mumbai by a noticeable margin. (The “historical average low” in Delhi in November is about 8 degrees Celsius lower than that of Mumbai in January). It is also less humid in Delhi than in Mumbai for the most part. One notable exception is the year 2012 when the Delhi race date was, annoyingly for most runners, brought forward to September! I will tell you how this too impacts the answer.
Terrain
The race route for Delhi is ‘pretty much flat’ whereas Mumbai has 2 noticeable inclines (the Bandra-Worli Sea Link and Peddar Road). In both cities, the races are held on motorable roads.

Calculations
Because Delhi is reputed to be faster, what interests me is “what is the time difference (in seconds) between Delhi and Mumbai run a few weeks later?”. So, I define
TimeDiff = Delhi – Mumbai
using the race records of “net time”.

Thus, a negative value indicates that Delhi is faster than Mumbai.  A positive value tells us that Mumbai was actually run faster than Delhi.

Racing ahead
I shall tell you the details of what I did over many tens of hours (of programming, number crunching and analysis) when I present this research in a live presentation one day.  For now, what might interest you more are the primary findings. And, pictorially, this is what they look like.

There’s no single number
There is no single “Delhi is faster than Mumbai by X minutes” that paints a decent representation. In fact the slower runners in Delhi get faster by the time they race in Mumbai.

The relationship is far from linear
One might expect that, as we examine slower runners, the difference grows such that Mumbai (hotter, more humid and with inclines) becomes increasingly slower.  Not only do we find the converse to be true, but also that it is not linear. This general relationship is seen when bucketing the time differences by race time buckets. The effect can be easily explained by the fact that often (not always, but, in general) the slower runners are also newer runners or are the type that train to race only in the primary racing season. Thus, even as they peak towards the end of the racing season (ending with the race in Mumbai) their fitness levels improve and they actually run Mumbai faster than Delhi.

2012 – The dreaded Delhi Year
In case you had not noticed, I excluded the data for Delhi from 2012 because that is the year the race was held in September, in weather that was considerably hotter (by about 5 degrees Celsius) than Mumbai in January. The impact of that is evident in the race timings. Once you adjust for the difference in weather, Delhi looks less attractive than Mumbai to obtain a better race time. Also, for the typical runner there was even more time to improve between Sep-12 (Delhi) and Jan-13 (Mumbai). I suspect that the additional training time had a greater impact than the weather difference.

Racing to the finish – what might you conclude?
So, what might you conclude from this? Well, if you are an experienced runner, run Delhi to get your fastest time in India. If you are new to running, and train to race mainly in the Sep-Jan season, then Mumbai will not be particularly slower than Delhi. In fact, you might even race faster in Mumbai than in Delhi. In that case, unless you are a Delhi lover or live close to it, reduce your carbon footprint and race only in Mumbai.

So far, so good…so what?
All that I presented is what the data tells us.  But you are not a number! You can pay attention to detail and focus on your goals without labels, avoiding bottlenecks and working with discipline to get to that higher level you have never been at before. Never mind the debate between Delhi and Mumbai lovers!

And now, I’d like your (anonymous) opinion please?

Dr Purnendu Nath spends his waking hours focusing on helping individuals and organizations reach their goals, to make the world a better place. He speaks, writes and advises on topics such as finance, investment management, discipline, education, self-improvement, exercise, nutrition, health and fitness, leadership and parenting.