The third and last issue that Mick and I took up was location of the navigation buttons. The MSI standard has been to put the Next button on the left and the Previous button on the right. We do this for three main reasons:
- Web users tend to read the page with a left side bias and placing the Next button on the left makes it easier to find.
- The Windows standard is to put the most often used functions on the left side. Think of the menu bar in Word and how often you access the drop downs going left to right.
- The default tab order sequence will activate the button on the left after a radio button is clicked. Hitting return will "press" that button. In earlier work we found that placing the Previous button on the left resulted in respondents backing up more often when it was placed on the right and the Next button was on the left. We believe this was accidental and undesirable.
- An experiment we ran a few years back suggested that respondents are indifferent on the issue, adapting quickly to whatever placement we presented.
In this research we had four experimental conditions:
- Next on the left and Previous on the right
- Previous on the left and Next on the right
- Both on the left with Next above Previous
- Next on the left and no Previous button
The effects we got were not necessarily dramatic, but they caused us to change at least one standard while reinforcing others:
- Taking away the Previous button resulted in more breakoffs. The difference was only about 3.4 percent but it was statistically significant.
- We replicated the results of the earlier study and saw a very slight but statistically significant tendency for respondents to back up more when the Previous button was placed on the left.
- None of the various treatments produced different results in the debrief questions that asked about enjoyment of the survey, ease of answering, length, etc.
- When the Next button was placed on the right completion times were slightly longer (16.1 vs. 15.2 minutes).
Taken as a whole, there is not much here to cause us to change our current standard. 
However, when we looked at how respondents answered grid questions with long scales we saw some evidence of an interesting pattern. When the Next button was on the left there was a slight tendency for the distribution of responses to lean to the left across an 11 point horizontal scale. When the Next button was placed on the right the distribution leaned slightly to the right. And so, placing the Next button on the right sometimes produced higher mean scores than placing it on the left. Why?
Two reasons come to mind. First, we know that eyetracking studies show Web users read in an F-shaped pattern, that is, focus more on the left hand side of the screen than the right hand side. By placing the Next button on the right respondents are forced to look there more and may end up processing more of the screen than they would normally and therefore are slightly more likely to select responses from that area of the screen. Alternatively, respondents may simply be saving "mouse miles," finding it easier and less effort to select responses from the right side when the Next button is placed there. We can’t tell which of these may be operating here. We probably need an eyetracking study to figure that out.
For now, moving the Next button to the right side of the screen seems like a risk worth taking. After all, one of the consistent problems with Web surveys is their tendency to yield lower satisfaction scores that telephone surveys. If moving the Next button to the right makes it more likely that the respondent will consider the full scale, that may be worth a little accidental backing up, especially since our debrief questions showed no obvious preference.