Will guessing affect the scores?

A common anxiety about objective tests is that students will gain an inflated score simply through guessing. The effects of guessing can be largely eliminated through the use of corrective scoring in which marks are subtracted for incorrect answers. Alternatively, as Brown et al (1997) points out, intelligent guessing can be viewed as a useful skill that lecturers may wish to encourage.

It's worth remembering that the relevance of guessing decreases as the number of test items increases.

See also the section on corrective scoring and the articles by Dr Jean McKendree on Guessing and Gender bias.