Slate's Daniel Engber takes a look at an issue right up our alley: Are weekend interviews problematic and do surveys condcuted on Friday and Saturday evenings skew toward Democrats?
Like many pollsters, I have an opinion on this issue less grounded in research findings than hard evidence. Over the years, the companies I have worked for have avoided weekend only surveys, on the theory, articulated by Engber that, "younger people are more likely to be out on Friday and Saturday nights, which would make them less likely to be included in the sample."
Remarkably though, little hard evidence exists to support the claim that weekend interviewing skews Democratic, and one key study indicates it makes little difference:
One of the best studies of this question was conducted by two polling experts at ABC News. Gary Langer and Daniel Merkle looked at the data from ABC"s tracking polls for the last three presidential elections. They compared results from people reached on Sunday through Thursday with those reached on Friday and Saturday and found no difference. Among the Sunday-to-Thursday people polled in 2004, 49 percent supported Bush and 46 percent supported Kerry. Polls of the stay-at-home, Friday-to-Saturday crowd produced similar numbers—48 and 46.
Engber's "Explainer" piece does a nice job summarizing the steps quality surveys take to interview those who are hard to reach. It's worth reading in full.