Questionnaire designers are encouraged to write questions as complete sentences. In self-administered surveys, incomplete question stems may reduce visual clutter but may also increase burden when respondents need to scan the response options to fully complete the question. We experimentally examine the effects of three categories of incomplete question stems (incomplete conversational, incomplete ordinal, and incomplete nominal questions) versus complete question stems on 53 items in a probability web-mail survey. We examine item nonresponse, response time, selection of the first and last response options, and response distributions. We find that incomplete question stems take slightly longer to answer and slightly reduce the selection of the last response option but have no effect on item nonresponse rates or selection of the first response option. We conclude that questionnaire designers should follow current best practices to write complete questions, but deviations from complete questions will likely have limited effects.