Credibility of exit/opinion polls

Context: Prediction of Election outcome through Exit polls and opinion polls have not been accurate.

Some examples where election prediction has miserably failed?

• The example of the Venezuelan recall referendum of 2004: The exit poll that predicted Hugo Chávez to be recalled however, Hugo Chávez won in the Venezuela Referendum
• In recent Bihar elections: The exit polls, mostly predicted a Rashtriya Janata Dal victory with huge margin however the NDA proved exit polls are wrong.
• US presidential elections 2016: Hillary Clinton consistently led Trump in national polls in 2016 however Trump won the election.

What are the reasons for such failures?

• Principles of statistics ignored: Pollsters do not follow the statistical principles properly in designing, sampling, and analyzing their data.
• Lacks holistic coverage: They do not cover remote corners of the country and cover sensitive booths for their surveys.
• No scope for Margin of error: The standard requirements of 3 percentage points as margin of error is not adhered.
• Selection bias: The samples selected by them does not maintain the proportions across gender, age, income, religion, caste, and other important factors.
• Issues in method of sampling: Non responses are not properly tackled and the aspect of ‘random’ sampling is not given adequate importance.

Evaluation of Budget 2021