Professor Betterknow conducted a longitudinal study about the sexual identity of students. In 2000, she asked in her questionnaire the participants the following question: "Please indicate your sexual identity". In 2002, Professor Betterknow asked the same participants in her questionnaire the same question. Betterknow found that in 2002 37% of the respondents gave a different answer than in 2000. This means that the measuring instrument is Question 22 options: not a precise measure the value on the variable must have changed for many respondents inaccurate unreliable lacking face validity