Are "internal polls" any more reliable than publically released polls? [View All]

[Bucky]

I sometimes here the phrase "internal polls" used to describe results that a losing candidate relies on. But aren't internal polls just surveys that a campaign takes and doesn't bother to release? Does anyone with experience in campaigns know if these use larger sampling sizes or different methodologies?

I used to work in market research, so I'm pretty familiar with random sampling methodologies and how size of sample can affect margins of error and confidence rates. But is there anything special or unique about internal polls that make them more reliable (or less) than the polls news organizations buy and report on?