Rating Scale Labels: Label End Points or Every Point?

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Your boss says that questionnaire you're writing should ask your customers "What is your overall satisfaction with our product?" and should use a five-point scale.  Sounds simple, you think to yourself, then go to write the question.  Which format do you use?

Like many other tactical issues regarding questionnaire design, scale formats have been carefully studied.  According to the summary of available research by Jon Krosnick and Leandre Fabrigar in "Designing rating scales for effective measurement in surveys":

• Respondents prefer rating scales with more verbal labels
• Respondents believe such scales provide more valid measurement
• Choosing a labeled choice is a more natural mental activity (not to mention more conversational) than selecting a number within a range
• Longitudinal reliability is greater when using fully labeled scales instead of partially-labeled scales
• Validity, especially inter-rater validity, is greater using fully labeled scales
• Using fully labeled scales provides greater reliability and greater validity from respondents with low to moderate education
• Because numeric values can confuse respondents and affect the choices they make, it is better to omit numeric labels altogether.

Given the importance of fully labeling a rating scale, choose an existing common scale where possible, rather than writing your own scale.  Reword the question if necessary to fit a common scale.  And, of course, take care when deciding how many points to use within the scale.