I sent Rick Claussen's memo, referenced below, to Mark Baldassare of PPIC, and asked him for a response to the claims on voter turnout. Here's what Mark wrote back:

"Thanks, our poll does not assume a specific turnout for the
election. In fact, we never make predictions about the size and
composition of the electorate before an election. We define likely
voters through answers to a series of questions about voter
registration, intentions to vote, past voting, interest in politics, and
attention to election news. Rather than focus on the size of our sample
as it relates to the percent of registered voters, let's consider the
partisan makeup among our likely voters -- Democrat 45%; Republicans
36%; dts/others=19%. Would a low turnout produce a more Republican or a
more Democratic electorate? This will be important, since Republicans
are  opposed to 1A to 1E will Democrats favor each of them...."

UPDATED 9 p.m.: Rick Claussen, the veteran initiative consultant handling the sweeping campaign for all six California special election measures, is out with an interesting memo on the recent PPIC poll, which shows five of those six in trouble.

Claussen is self-interested obviously. But your blogger has found him to be very reliable in the past. (Most recently, your blogger said Prop 11, last November's redistricting initiative in California, had no chance of passing. Claussen told me I was wrong and then proved it, managing the campaign that got it passed).

In this new memo, dated Wednesday, Claussen writes that the PPIC poll effectively assumes a turnout of 50 percent. He says the campaign's own internals on Prop 1A show it with a lead of 50 to 37 percent. That would make the measure hardly a sure thing, but that's much better than the PPIC poll, which showed it trailing, with 46 percent No and 39 percent Yes:

From the memo:

Rick Claussen, the consultant and initiative expert who has been brought in to help qualify the current redistricting initiative in California, got in touch this week. Claussen, who works from the Sacramento suburbs, is one of the grown-ups in the direct democracy business and has one of its strongest records, particularly in winning "yes" campaigns, which are much more difficult than "no" campaigns. He worked on previous Schwarzenegger ballot campaigns in 2004 and 2005, and he expressed confidence by email that the redistricting measure will qualify in time for the November ballot.

Claussen says the initiative is on track to hit its target of 1.1 million signatures the first week of May; signatures will be submitted the week of May 12. That number of signatures is nearly twice the 694,354 legally required to make the ballot. But in the initiative business, it is standard operating procedure to submit hundreds of thousands more signatures than legally required -- in large part to speed up the qualification process. When more signatures than required are submitted, county elections officials -- who do the counting in California -- can count using "random sampling" techniques, rather than by going through every signature. If the random sample shows that the number of valid signatures is greater than 110 percent of the legally required number (and a validity rate of 70 percent is considered good in this business), then the initiative automatically qualifies for the ballot. This makes things much faster.