Visualising the effectiveness of India's COVID-19 lock down
While there has been broad speculation about the benefits of the nationwide lock down in India, if we look at its day-on-day growth rate, the issue becomes easier to comprehend with clear evidence of its effectiveness.
In this graph, we plot the percentage increase in the total number of cases over the previous day. To arrive at this number, we use the previous day's cases as the base. The numerator is the difference between the cases today and yesterday. As we can see, this number had been volatile and touching 30% before the lock down. This means on a base of 600, there would be ~200 new cases.
Now, if we move towards the centre, we see the lock down formally announced on 23rd of March to be effective from 24th of March. While the daily growth rises and falls for a week after the announcement, if we look at two weeks since the decision of the lock down, we see that it has considerably eased. Since the incubation period of the virus is taken between 6 to 14 days, we start seeing the dip roughly 10 days later. This is consistent with the impact of government actions in other countries. After peaking at 26%, the number has constantly gone down. Once the migration problem started, in which millions of migrant labourers were heading back to their villages and towns, there were prohibition orders that required district closures to prevent this large-scale movement. As a result, if we look at the period two weeks after this prohibition order, the dip in the total percentage of new cases becomes very evident. This graph highlights the effectiveness of the ongoing national lock down and further illustrates how its stricter enforcement would lead to lower number of new cases.
It is important to note that this approach is superior as compared to the total number of cases approach. This is because adding 600 new cases will look the same if we plot the total number of cases whereas it would not be sensible to equate 600 new cases on a base of 3,000 as against 600 new cases on a base of 10,000. Anyone would agree that 600 new cases on a higher base is better as it indicates a lower spread of infection. We celebrate and support the decision of the Prime Minister of India to extend this lock down and to ensure that it is strictly enforcement across the country.
Formula for % growth in cases = (Total cases today- Total cases yesterday) X 100 / (Total cases yesterday)