1. Open the CSV (comma-separted variables) file created by FormScanner.
  2. Download ProcessBubbles from the Downloads tab.
  3. Enter the number of questions (not including ID #) in cell C1, and the answer to each of the questions in the same row.
  4. Delete cells A2 and A3.  Copy the results from Formscanner in row 2 and below.  The cell after the last row must be empty.
  5. Type ctrl-p to process the information.
  6. Correct scores are yellow;  incorrect scores are green; and  invalid answers (either multiple response when not warranted or no answer at all) are red.  The following information is provided:
    • Item facility: the fraction of students who chose the correct answer on that question (# correct/total # of students).  The item facility is also known as the question difficulty.  Low values indicate difficult questions.  A good exam should have questions with a variety of difficulties.
    • No. of students: the total number of students who took the exam.
    • Q1: the lower quartile
    • Q2: the middle quartile or median of the class' scores
    • Q3: the upper quartile
    • Avg top --: the average of the students in the top quartile (>= 75th percentile).  In this example, the set included 2 students.
    • Avg bottom --: the average of the students in the bottom quartile (<= 25th percentile).  Here, it included 2 students.  
    • Discrimination: The averages of the top and bottom quartiles are given also for each question (correct=1, incorrect=0).  The discrimination is the difference between these two values.  A large discrimination (the max is 1) means the well-performing students scored well on that question; a low discrimination means poor-performing students scored well.  The discrimination should be >0.20; if the discrimination is less (or negative) check the key or consider revising the question.

See this site for more information about item analysis:

http://sites.psu.edu/itemanalysis/