WHO methodology to estimate the COVID-19 death toll

In News

• India questioned the World Health Organisation’s methodology to estimate the COVID-19 death toll in the country which claims 4 million COVID deaths. 

About the methodology

• The model assumes an inverse relationship between monthly temperature and monthly average deaths, which does not have any scientific backing to establish such a peculiar empirical relationship.
•  The analysis uses mortality figures directly obtained from Tier I sets of countries, and uses a mathematical modelling process for Tier II countries (which includes India).
• The Global Health Estimates (GHE) 2019 on which the modelling for Tier II countries is based, is itself an estimate.
  • The present modelling exercise seems to be providing its own set of estimates based on another set of historic estimates, while disregarding the data available with the country.
• In order to calculate the age-sex death distribution for India, WHO determined standard patterns for age and sex for the countries with reported data and then generalized them to the other countries that had no such distribution in their mortality data.
  • Based on this approach, India’s age-sex distribution of predicted deaths was extrapolated based on the age-sex distribution of deaths reported by four countries (Costa Rica, Israel, Paraguay and Tunisia).
• Of the covariates used for analysis, a binary measure for income has been used instead of a more realistic graded variable.
  • Using a binary variable for such an important measure may lend itself to amplifying the magnitude of the variable.
• The test positivity rate for Covid-19 in India was never uniform throughout the country at any point of time.
  • But, this variation in covid-19 positivity rate within India was not considered for modelling purposes.
• Containment involves a lot of subjective approach: such as school closing, workplace closing, cancelling of public events etc to quantify itself.
  • But, it is actually impossible to quantify various measures of containment in such a manner for a country like India, as the strictness of such measures have varied widely even among the States and Districts of India.

• The model gives two highly different sets of excess mortality estimates when using the data from Tier I countries and when using unverified data from 18 Indian States.
  • India has asserted that if the model is accurate and reliable, it should be authenticated by running it for all Tier I countries and if the result of such exercise may be shared with all Member States.

Issues raised by India 

• Population Size: The concern specifically includes on how the statistical model projects estimates for a country of geographical size & population of India and also fits in with other countries which have smaller populations.
  • Such one size fits all approaches and models which are true for smaller countries like Tunisia may not be applicable to India with a population of 1.3 billion.
• Wide variation in estimates raises concerns about validity and accuracy of such a modelling exercise.
• India is a country of continental proportions climatic and seasonal conditions vary vastly across different states and even within a state and therefore, all states have widely varied seasonal patterns.
  • Thus, estimating national level mortality based on these 18 States data is statistically unproven.
• It is not clear as to why GHE 2019 has been used for estimating expected deaths figures for India, whereas for the Tier 1 countries, their own historical datasets were used when it has been repeatedly highlighted that India has a robust system of data collection and management.
• The detailed justification of how the combination of variables is found to be most accurate is yet to be provided by WHO.
• Subjective approaches to quantify measures will always involve a lot of biasness which will surely not present the real situation.
• Some fluctuations in official reporting of COVID-19 data from some of the Tier I countries including USA, Germany, France etc. defied knowledge of disease epidemiology.
• Issues in categorization: Inclusion of a country like Iraq which is undergoing an extended complex emergency under Tier I countries raises doubts on WHO’s assessment in categorization of countries as Tier I/II and its assertion on quality of mortality reporting from these countries.

Way forward

• India has undertaken COVID-19 testing at a much faster rate then what WHO has advised.
  • India has maintained molecular testing as preferred testing methods and used Rapid Antigen as screening purpose only.
  • Whether these factors have been used in the model for India is still unanswered.
• India has remained open to collaborate with WHO as data sets like these will be helpful from the policy-making point of view. The country believes that in-depth clarity on methodology and clear proof of its validity are crucial for policymakers to feel confident about any use of such data. 
• India has expressed above and such similar concerns with WHO but a satisfactory response is yet to be received from WHO.
  • WHO is yet to share the confidence interval for the present statistical model across various countries.

Source:LM