But your link does not support claims of "observation bias", but rather my explanation: the "self-biasing sample":
"The most likely source of this error is differential non-response rates for Democrats and Republicans..."
It gives no evidence --- nor even mere opinion --- that the discrepancy is caused by the pollsters.
"Observation bias" doesn't mean the observers are biased. It simply means that sometimes, the very act of making an observation biases the results. The pollsters caused the discrepancy simply because they asked people who they voted for, which is a question that democrats are more likely to answer.
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