No, Hillary and Donald aren't tied

The CBS / NYT poll released today is getting a ton of media because it says that Hillary and Donald are tied nationally. Of course, I had to dig into the numbers to figure out what was going on. You probably already know that, after adjusting the numbers to reflect the true nature of party affiliations in the US, the CBS / NYT is misrepresenting reality.

It turns out that their polling continually overrepresents 'independent' respondents. We know from Gallup that when you push self-identified independents to identify a party they most frequently align themselves with, most of them will pick one of the two parties. As such, Gallup shows that registered voters across the US are roughly aligned 48% Democrats + Leaners and 42% Republican + Leaners, with the rest, 10%, truly unaligned (according to the most recent Gallup data, dated June 14 - 23).

If you simply group all independents together, your data can be easily swayed by poor sampling of independents. For instance, if you oversampled the Pacific Northwest you'd likely get a vastly more liberal result than if you oversampled independents from the South. That is why applying leaners, matters.

July CBS / NYT poll, adjusted

The July CBS / NYT poll weighted respondents 27% Republican, 33% Democrat, 39% Independent. Applying Gallup's party affiliation from June 14 - 23 (D+L = 48%; R+L = 42%; I = 10%) to CBS / NYT weighted numbers, instead of the tied 40% - 40% poll, we get an implied poll showing Hillary up 42% - 38%.

June CBS poll, adjusted

It wasn't enough to analyze their July poll to understand what they did; if they had dramatically altered the weighting between June and July, it could be interpreted as an attempt at push-polling; they didn't. The June CBS poll weighted respondents 28% Republican, 35% Democrat, 37% Independent. Applying Gallup's party affiliation from June 1 - 5 (D+L = 48%; R+L = 41%; I = 11%) to CBS's weighted numbers, instead of the 39% - 32% poll favoring Hillary, we get an implied poll showing Hillary up 42% - 36%. This adjusted poll shows Hillary with an implied +6 point gap compared to CBS poll's +7 point gap.

So, after adjusting their polling, it turns out Hillary has a +4 point margin, slightly less than the +6 point margin in June. I suspect that, were I to go back and apply the nearest Gallup party affiliation data to every poll out there, we'd get something closer to uniform polling, all showing Hillary up against Donald.