Little Day of Week Bias in Polling Data

One of the great challenges in conducting any survey research is the possibility of structural bias in the data collection process. One possible bias is that surveys on a particular day of the week may produce different results than some other day.

At, we recently compared the results of data collected each day of the week and found a reassuring level of consistency.

For all surveys launched on Sunday nights, the president’s Job Approval rating was at 46%. It was 47% for surveys launched on Monday and Wednesday. On Tuesday and Thursday launches it was 48%. For each of those days, we conducted more than 10,000 interviews with registered voters.

We launched a much smaller number of interviews on Friday nights, but the results were also broadly consistent and average a 48% approval rating.

On the Generic Congressional Ballot, the consistency was the same. On average, Democrats led by 6 to 8 percentage points regardless of the day the poll was launched. will soon be releasing both the president’s Job Approval ratings and the Generic Congressional Ballot on a daily basis. When we do, we will release results on a three day rolling average basis. This provides even more consistency and continuity than the single day numbers.

See a summary of day by day results.



Posted in Poll Results

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