 7.4 Searching for Item Statistics - Maple T.A. 2016 Help Instructor
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## 7.4 Searching for Item Statistics

1. Click Item Statistics.
1. In the Select Assignments tab, select the assignments you want to include in the search.
• To select multiple assignments, hold down the Ctrl key (Command, on Mac) to select more than one assignment.
 Success Rate The Success Rate of an item is the average normalized score on that item. With each item graded between 0.0 and 1.0 (that is, normalized), the average score is computed over the set of all scores recorded for that item in the current assignment. p-Value The p-Value of an item measures the proportion of students who got the item correct. It is defined as the ratio of the number of fully correct responses to the total number of responses in the data set. That is, where n is the number of responses and F is the number of fully correct responses. d-Value The d-Value measures the discrimination of an item. To calculate it, the dataset is divided into two groups based on the scores on the entire assignment. The sets consist of those that scored greater than (or equal to) the median grade on the assignment and those that scored less than the median grade on the assignment. The p-Value for each set is calculated, and the d-Value is the difference of the p-Value for the high-scoring group and the p-Value for the low-scoring group. wheren1 = number of assignments with scores median grade for the assignmentn2 = number of assignments with scores median grade for the assignmentF1 = number of fully correct responses on this item from the top-scoring setF2 = number of fully correct responses on this item from the bottom-scoring set p-Biserial The p-Biserial is a correlation coefficient relating performance on an item and performance on the total assignment. The p-Biserial correlation coefficient is an index of discrimination that measures the extent to which students who score high on the assignment tend to get the item correct and those who score low tend to get the item incorrect. where = mean grade of assignments on which this item was answered incorrectly. = mean grade of assignments on which this item was answered fully correctly.p = p-Valueq = 1-p = standard deviation for assignment grades r-Biserial The r-Biserial is a correlation coefficient relating performance on an item and performance on the total assignment. The r-Biserial correlation coefficient is an index of discrimination that measures the extent to which students who score high on the assignment tend to get the item correct and those who score low tend to get the item incorrect. where = mean grade of assignments on which this item was answered incorrectly. = mean grade of assignments on which this item was answered fully correctly.p = p-Valueq = 1-p = standard deviation for assignment gradesY = height of the standardized normal distribution at the point z, where P(z'z)=p  Note: Since the r-Biserial is scaled by a parameter that is based on a normal distribution, it can result in values outside of -1 to 1 if the scores are not normally distributed.