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Little Day of Week Bias in Presidential Tracking Poll

One of the ongoing debates about polls and polling involves day-of-the-week-bias. Are some polling days more favorable to Republicans and others more favorable to Democrats?

A review of data from the Rasmussen Reports daily Presidential Tracking Poll since Barack Obama clinched the Democratic nomination shows little variance based upon the day of release. From June 4 through July 29, the average lead reported for Obama was 4.6 percentage points.

The average result reported on Monday and Saturday was precisely the same—4.6 percentage points. Two other days were within two-tenths of a percentage point of the overall average—Tuesday’s showed Obama leading by an average of 4.8 percentage points while Friday showed a 4.4 point Obama lead on average.

Wednesday’s average was just three-tenths of a point better for McCain while Thursday averaged a half-point better for the Republican. The biggest discrepancy came on Sunday—results released on that day showed Obama up by an average of 5.3 percentage points. That’s seven-tenths of a point better for the Democrat than the overall average.

Keep in mind that the daily Presidential Tracking Poll results are reported on a three-day rolling average basis. So, results released on any day of the week were collected over the preceding three days.

Day by Day Presidential Tracking Poll AverageJune 4-July 29, 2008

 

MonAvg

Tues Avg

WedAvg

ThursAvg

FriAvg

SatAvg

SunAvg

McCain

40.8%

40.5%

40.9%

41.1%

40.9%

40.9%

40.6%

Obama

45.4%

45.3%

45.1%

45.3%

45.3%

45.4%

45.9%

Obama +

4.6%

4.8%

4.3%

4.1%

4.4%

4.6%

5.3%

The fact that some days show a slight variance does not necessarily mean there is any day-of-the-week bias. It could reflect slightly different phases of the campaign. For example, this past Sunday’s release included polling interviews conducted on Thursday night, Friday night, and Saturday afternoon. Thursday was the day of Obama’s Berlin speech which showed a significant but temporary bounce in support for the Democrat. That bounce alone could account for much of the difference between the average Sunday results and the average for all days.

The same pattern is found when the results are examined with leaners.

The average for the entire period with leaners was a 3.8 percentage point lead for Obama. Four of the seven days of the week came within one-tenth of a point of that overall average (Monday, Tuesday, Thursday, and Friday). Two days showed results half-a-point better for McCain on average while Sunday’s average was nearly a point better for Obama.

Day by Day Presidential Tracking Poll Average With LeanersJune 4-July 29, 2008

 

MonAvg

Tues Avg

WedAvg

ThursAvg

FriAvg

SatAvg

SunAvg

McCain

44.4%

44.4%

44.6%

44.9%

44.4%

44.3%

43.7%

Obama

48.3%

48.1%

48.1%

48.1%

48.1%

48.0%

48.4%

Obama +

3.9%

3.8%

3.5%

3.2%

3.7%

3.7%

4.7%

It should be noted that the daily Presidential Tracking Poll is a fairly large sample survey. One thousand interviews of likely voters are conducted each night for a three-day rolling average sample of 3,000 Likely Voters.

National

Latest RR Poll

With Leaners

Electoral College

Fav Rating

Ras Mkts

McCain (R)

45%

46%

163

55%

Obama (D)

50%

52%

260

56%





About Rasmussen Reports

Rasmussen Reports is an electronic publishing firm specializing in the collection, publication, and distribution of public opinion polling information.

The Rasmussen Reports ElectionEdge™ Premium Service for Election 2008 offers the most comprehensive public opinion coverage ever provided for a Presidential election.

Scott Rasmussen, president of Rasmussen Reports, has been an independent pollster for more than a decade.