Wednesday, June 29, 2016

Test Performance Profile

The Test Performance Profile (see below) was invented to guide item, test, student, teacher and instruction development. Item, Percent Difficulty, and Discriminating are listed in each column sorted first by item and then by difficulty for Master/Easy, Unfinished, and Discriminating.

The high scoring RMS nursing test has far more mastery items than the other two categories. The KJS biology test has far more discriminating items then the total of the other two categories. It also has item 9 flagged as BAD. It may need to be dropped and the test re-scored.

Low scoring Unfinished and highly Discriminating items need to be discussed in class. This information is examined in greater detail in the Student Counseling Matrixes.

Standardized tests do not contain Mastery/Easy and Unfinished items. The goal is to obtain the needed distribution of scores with the fewest items. Discriminating items have a far higher Avg PBR (0.39 and 0.40) than Mastery (which has near zero) and Unlimited (0.12 and 0.15).

Test reliability or reproducibility is estimated by KR20 and alpha. It increases with the length of the test and with discriminating items.  

The Discriminating, 50 item and 100 item values for reliability, are surprisingly close for these two tests with very different students (nursing and general biology), student preparation, and assessment (RMS and KJS). In summary, teacher skill takes precedence over statistics in selecting questions for a test. 

The nursing test measures mastery. The biology test measures the different things that students found of interest in reading assignments and other course actives: lecture and laboratory. The biology students did a good job in picking items to report what they knew and what they had yet to learn (only 9 Unfinished). 

The two columns for Unfinished and Discriminating for biology may look similar to those for nursing if the biology students were forced to guess. The practical, useful, details are in the Student Counseling Matrixes.

Right Mark Scoring (RMS)

Knowledge and Judgment Scoring (KJS)

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