The Missing Piece !
Feels like an eternity right ? But it has been just few months since the world got to know about the novel corona virus and less than a month we Sri Lankans are stuck home due to this catastrophe. And every single day we see increasing numbers of COVID 19 infections despite the incredible efforts of the Sri Lankan government ,tri forces and health officials along with island wide curfew being imposed.
I often thought to myself, What actually is the Missing Piece?
Considering the situation in the country,Sri Lanka has imposed rolling curfews with breaks for most districts , while Colombo, Gampaha, Puttlam, Jaffna and Kandy which have been identified as High Risk areas are under permanent curfew.
The “ High Risk / Unsafe” areas declared are those reporting most number of cases. Being a person who studied statistics for more than 4 years, I see some sort of Bias in deciding these High Risk areas. I see we are missing on some important information. In Statistics, this is classically known as Survivor-ship Bias.
What is Survivor-ship Bias ?
It’s a form of selection bias caused when we only focus on the survivors of the particular scenario. In other words, survivor-ship bias occurs when you draw hasty conclusions from an incomplete data set which only consist data on the “survivors” which often is quite a non representative sample.
The famous Historical Illustration:
Abraham Wald who was a famous statistician during the World War II, was given the task of figuring out “How to improve fighter planes” . He inspected and gathered data from the planes that returned from war zones. It’s common sense that one can observe the damage suffered by different parts of the plane and conclude that those parts that were riddled with bullets to be armored further.
But Wald saw the misconception of common sense. He realized that,it was the parts of the planes that were least riddled with bullets are those needed to be armored because the surviving planes showed where the planes could suffer damage and still survive. He further elaborated, the planes that never came back were missing from his data set and those could be the planes which received a bullet somewhere else. So these were the areas that needed to be shielded. This is one fine example of survivor-ship bias!
COVID -19 and Survivor-ship Bias
Similar to the above scenario, The High Risk Areas are defined based on the available data of the confirmed cases. In other words,the High Risk areas are those areas where there’s a lot of testing based on contact tracing while the Low Risk areas are those with no/limited testing. But as given in the above illustration, most of the useful data could be missing !
The curfew is being lifted for few hours in areas defined as low risk. The people in these areas are less concerned about the threat since the number of COVID 19 cases are null or negligible which is a common sense decision based on the available data.But the virus may be in the community, and it could spread in the low risk areas too.The difference in case counts between different regions is not a direct measure of the difference in coronavirus spread in these places! This is because there are many often-unobserved factors.
What is the Missing Piece?
Ideally the safe and unsafe areas should be decided based on data which come from extensive testing. No test , No Positive! In my previous article , I explained how countries like China and South Korea controlled the spread of corona virus to a great extent.The most of it was done through extensive testing. South Korea has tested more people per capita than any country in the world — a total of nearly 300,000 people. Thus, the missing piece is Extensive Testing !
So on good news is, Sri Lanka is to begin sample Covid-19 testing.As of now the Sri Lankan authorities are tracking contacts of confirmed cases most of whom were Wave II arrivals from abroad or their family members. However this should be extended to testing samples from different parts of the island to overcome the so called survivor ship bias.
So until regular testing becomes prevalent in the country, its vital for us to determine the high risk areas based on not only the current confirmed cases but also estimates of the people who are susceptible to the virus.No one single estimate will be perfect, but without any there could be a lot of irrational decisions made. For now let’s just assume the spread of the virus is bigger than what’s being heard and reported.
So, until the missing piece is patched , it’s not safe outside. Stay indoors and Stay Safe !
