This may introduce a source of error into the poll.

The practical difficulties of conducting any survey may also introduce other souces of error into the poll.

In addition, the practical difficulties of conducting any public opinion survey may introduce other sources of error into the poll.

In addition to sampling error, the practical difficulties of conducting any opinion survey may introduce error into the poll.

In addition to sampling error, the practical difficulties of conducting any survey of voter opinion on caucus day, like some voters changing their minds after they enter the caucus, may introduce other sources of error into the poll.

In addition to sampling error, the practical difficulties of conducting any survey can introduce other sources of error into the poll.

In addition to sampling error, the practical difficulties of conducting any survey of voter opinion at polling places, like the reluctance of some voters to take time to fill out the questionnaire, may introduce other sources of error into the poll.