A number of polling firms routinely measure the president’s job approval ratings. Generally, they all show a similar trend even when the specific numbers are different.
There are a number of reasons for this, including:
Likely Voters or Adults? - Some firms poll all adults while others, including Rasmussen Reports, base their results on likely voters. Generally speaking, polls of all adults will show a somewhat higher rating for President Obama than polls of likely voters.
Why is this? Primarily because some demographic groups such as young adults are less likely to vote than others. These same groups also happen to be segments of the population where the current president gets rave reviews. So if a poll of all adults shows the president’s approval rating at 60%, you’d expect a comparable poll of likely voters to show a rating of roughly 57%.
Question Wording - Rasmussen Reports offers survey participants a choice between Strongly Approve, Somewhat Approve, Somewhat Disapprove and Strongly Disapprove. Some firms offer simply Approve or Disapprove while others offer a scale that includes Excellent, Good, Fair or Poor. It is impossible to determine exactly what impact the different wording has on survey results.
However, it appears that the Somewhat Approve and Somewhat Disapprove categories may encourage some people to voice a minority opinion rather than saying they are not sure. In other words, when a president is popular, a segment of the population might say they Somewhat Disapprove. When a president is unpopular, some might say they Somewhat Approve.
Methodology - Rasmussen Reports uses an automated polling methodology while some firms use operator-assisted techniques. Generally, these different methodologies generate about the same level of approval for different political figures, but the automated technology generally registers a higher level of disapproval. There’s no way to be sure why this happens, but it may simply be that some people are reluctant to offer a negative opinion about another human being to a live operator.
Regardless of the reason, Rasmussen Reports surveys tend to have lower levels of no opinions and higher levels of unfavorable opinions for political figures. But, as with the topline numbers, the trends all move in the same direction.
It is interesting to note that the number who Strongly Disapprove in a Rasmussen Reports survey is similar to the number who say they Disapprove in most operator-assisted surveys.