Latest YouGov Poll Jul14-16

[bluewater]

Jul 14-16, 2019 572 responders
538 B rated : YouGov poll

Biden..... 21% last week, 23% this week
Warren... 18% last week, 15% this week
Sanders.. 10% last week, 13% this week
Harris..... 13% last week, 10% this week
Buttigieg.. 9% last week, 7% this week

Biden lead +3 last week, +8 this week

Margin of Error: +/-3% for registered voters

https://today.yougov.com/(popup:search/democratic%20primary)

Disclaimer: This is an early poll. No single poll result, especially this early, should be over emphasized.

Movement in this poll is in the 2-3% range from last week, which is within the margin of error.
Another poll showing another essentially unchanged week, are voters in a holding pattern until the next debate?

[honest.abe]

1. I would say going from a 3 point lead to an 8 point lead is significant.

Right?

[bluewater]

2. Certainly significant enough to be noted prominently in the op! ;)

Last edited Wed Jul 17, 2019, 01:05 PM - Edit history (3)

But then, all candidate movement was within the poll's 3% margin of error, so lets see what the STATICIANS have to say about leads:

3 Difference between two polls

A different issue is posed by the difference of proportions between two independent polls. Given two polls we want to know if opinion changed by a statistically significant amount from one poll to the next. Unlike the case within a single poll, here the percent support for a candidate in one poll is independent of that support in the other poll. (Because we draw independent random samples for each poll, this will be the case.) Now the difference of interest is p2?p1 where the subscripts 1 and 2 indicate polls 1 and 2, and we are measuring support for the same candidate in both polls. The variance of the difference with independent samples is Var(p2?p1) = Var(p1)+Var(p2) = p1q1 n1 + p2q2 n2 where q1 =1?p1 and q2 =1?p2, so the margin of error becomes CI(p2?p1)=1.96sp1q1 n1 + p2q2 n2 This is not twice the margin of error for either poll (and the MOE for each poll may differ.) If the margin of error is the same for both polls, then the MOE for their difference is 1.41 times the MOE for the polls, not 2 times it. Why the difference? Within a single poll, if support for the Democrat goes down, support for the Republican must go up if there are no undecided or third party voters. (If there are third alternatives then the proportions are likely to still be correlated, just not perfectly.) The formula for the difference of multinomial proportions given above takes this nonindependence between the proportions into account. In contrast when we compare across two independent samples, the proportion support estimated for the candidate in each poll is statistically independent because the samples are drawn independently. Hence a different formula for the independent samples case.
4 Examples
A Time magazine poll conducted January 22-23, 2007, surveyed 441 registered voters who are Republicans or lean Republican. The margin of error for the poll would be MOE = 1.96×s.5×.5 441?1 = .0467 ? .05 or 5% The Time poll found support for Senator John McCain at 30%. Former Mayor Rudy Giuliani received 26% support. The McCain lead over Giuliani is 4 points, but what is the margin of error? Using the “twice the MOE of the poll” rule, this would fall clearly short of 2×.0467=.0934 or just over 9 point MOE for the difference.
5
Using the correct formula for the MOE of a difference, we get MOE(McCain?Giuliani) = 1.96×sp1+p2? p1?p2)2 441?1 = 1.96×s.30+.26? .30?.26)2 440 = .0698 ? .07 or 7% So the margin of error of the difference is 7 points and the difference of 4 points is not outside the MOE, and we conclude that the McCain lead is not statistically significant in this case. An example where this distinction does matter is provided by a Public Policy Polling (PPP) survey of North Carolina Republican primary voters, taken February 5-6, 2007.4 This poll of 735 respondents found support for Giuliani at 31% with former Speaker of the House Newt Gingrich at 25%. The margin of error for this poll is .036, using the standard calculation for a single question. If we use the “twice the MOE” rule, the MOE for the difference between Giuliani and Gingrich would be 2×.036=.072 or 7.2%. In that case, the six point Giuliani lead would not reach statistical significance. If we apply the correct formula for differences of multinomial proportions, using p1 =.31 and p2 =.25, then the MOE is .054, or 5.4%, in which case the Giuliani lead is outside the margin of error and we would be justified in calling this a statistically significant lead. Nowconsiderthedifferencebetweentwoindependentpolls. IntwoAssociatedPress/Ipsos polls, approval of President George W. Bush’s handing of his job was at 36% in a January 16-18, 2007 poll of 1002 adults, and at 32% in a February 5-7, 2007 poll of 1000 adults. Is this difference statistically significant? The MOE for the polls is .031, or 3.1% for both polls. Since the polls were conducted independently, the MOE for the difference in approval is MOE(p2?p1) = 1.96×sfrac.36×.641002?1+ .32×.68 1000?1 = .0415 or 4.15% The change of 4 percentage points is slightly less than this margin of error, so the change in approval is not quite statistically significant.

https://abcnews.go.com/images/PollingUnit/MOEFranklin.pdf

Note: the emojis are from the forum misinterpreting the quoted text.

So, it seems a +8% lead IS statistically significant, but by less than one would think. The margin of error for the lead would be a bit less than twice the margin of error for a given candidate's support, making that in this poll roughly 5 to 5.5%.