Hemali Chhapia | TNN | Updated: Jul 20, 2020, 05:35 IST

Medical personnel check temperature of a Dharavi residents in MumbaiMUMBAI:

What is the rate at which Covid-19 cases in the city are doubling? It may look like simple math, but is the BMC, which claimed the answer was over 50 days, correct?

Mumbai crossed 50,000 cases on June 9. On July 18, the count stood at 1,00,178. Thus, it took 39 days for the number of Covid-19 positive cases in Mumbai to roughly double.

“Despite this, BMC has been claiming that the doubling period for Mumbai has crossed 50 days,” said Mumbai University economist Neeraj Hatekar in his paper, ‘Mumbai’s Doubling Period: Are we Getting It Right?’

‘Feel-good false numbers won’t help fight virus’

This is not the first time BMC reported a doubling rate that does not match the data. On June 26, the civic dashboard claimed a doubling period of 40 days. A look at the data showed that it had taken 28 days for case numbers to double and reach 70,878 on June 26.
“Data is important and good data analytics can help fight pandemics like Covid-19. But the data analytics must be well founded in good scientific practice. Otherwise, false numbers can make us all feel good, but will not help fight the situation,” said Hatekar.

“While it is indeed true that the Covid-19 situation in Mumbai is not as bad as that in certain other parts of the country and even the state, it is simply not true that the doubling period of Covid-19 cases in Mumbai has crossed 50. The BMC has been maintaining this because of a faulty analytical method,” he said.

While BMC does not reveal the formula it uses, a particular approach reveals the answer, said Hatekar. Give or take some rounding off using logarithms, and we get the BMC’s doubling period, he explained. “But this is not the actual doubling period at which cases are doubling. It is a hypothetical period that would elapse if the growth rate continued to be the same and cases were growing exponentially.”

Equally erroneous is the city’s guardian minister, who he said, picked it from the BMC dashboard and tweeted about it. While the doubling period in Mumbai is increasing, it is yet to cross 40 days, said Hatekar.