Choose a conceptual variable that can be considered to be a trait of interest to you, and (after conducting a literature review) create a 20-item Likert scale to assess it. Administer the scale to at least 20 people.
Compute the scale's reliability, and then, using a statistical software program, delete items until the scale's reliability reaches at least .75 or stops increasing.
Consider what sources of random and systematic error might be found in the scale.