I did a recent post arguing that Gallup's piece on labor day leads was misleading since they compared Bush's LV lead this year to (mostly) RV leads from previous races. They should have, I argued, compared apples-to-apples, RVs to RVs.

Frank Newport of Gallup was sporting enough to print an edited version of my comments on their editors' blog, along with his reply. In Newport's reply, his key rationale for conducting their analysis the way he did was he wished to "[use] Gallup’s best available estimates at Labor Day for each year for which we have data." (But by all means read his argument in full through the link.)

To further this discussion, here are some additional remarks on the issue replying to Newport's argument. I should add that I don't believe that Gallup has any particular axe to grind in how they did this analysis--I just think in this case they got it wrong.

Thanks for your thoughtful reply. But I still don't buy it. You surely must see that it makes a difference when people read these analyses with "7 point deficit to overcome" in mind rather than "1 point deficit to overcome"? And in fact that's how your analysis was written, focusing reader attention on the 7 point LV deficit.

And the fact remains that apples-to-apples comparisons are far preferable to apples-to-oranges comparisons. Therefore the proper comparison is between this year's RV labor day results and previous years'. Otherwise, you are not analyzing the same change (RV labor day gap vs. final gap) across years. (By the way, thanks for drawing my attention to the national adults samples prior to 1952. In the same apples-to-apples spirit, I would drop these cases from the analysis.)

Using a consistent time series would make a difference to your analysis.

Instead of:

"In summary, the history of presidential elections since 1936 suggests that in about half of the cases, the type of gap change that would be necessary for Kerry to tie or move ahead of Bush has occurred. About half the time it has not. If a gap change does occur, the odds are higher than 50-50 that it would be in Kerry's direction (i.e., a shrinkage rather than an expansion of Bush's current lead). "

You would have:

"In summary, the history of presidential elections since 1952 suggests that in all cases, the type of gap change that would be necessary for Kerry to tie or move ahead of Bush has occurred. If a gap change does occur, the odds are very strong (11 out of 13) that it would be in Kerry's direction (i.e., a shrinkage rather than an expansion of Bush's current lead)."

This clearly sounds quite a bit different. And thinking Kerry is behind by one point, rather than 7 points, clearly makes a big difference when considering elections like 1960 and 1980, which loom large in your analysis. Kennedy was behind by a point in 1960 among RVs--the same as Kerry--and Reagan was behind by 4 points in 1980--more than Kerry. If you're thinking 7 points behind, those races look a lot different.

In short, lacking a consistent time series of any length on LVs, you just shouldn't use 'em in an analysis like this.