Wainer observed, “I expect that future item analysis will surely have two characteristics; it will be graphical in presentation and dynamic in character” (1989, p. 192). Graphical methods generally appeal to SMEs who are less statistically minded.
A trace line is a plot that shows the number or percentage of examinees in each of several score groups (based on their total scores) who answer the item correctly. Other terms for a trace line are item characteristic curve or operating characteristic function. From the tabular data presented in Table 20.2, we can create a trace line that shows the pattern of discrimination across 10 score groups. Figure 20.1 show the trace lines for the right answer and a combination of all incorrect choices. The trace line for the right answer rises from low score groups to high score groups. The set of wrong answers has a trace line that falls from low score groups to high score groups. Trace lines are very effective for communicating item discrimination. Computer programs that are produce trace lines are LERTAP (www.assess.com), ITEMAN 4 (www.assess.com) and RUMM (www.rummlab.com. au/), among others.
Figure 20.1 Trace lines for the cumulatively incorrect and correct answers.