Using Split-Half Reliability With Tests
INSTRUCTIONS
Split-Half Reliability is a common statistical method used to determine the reliability of a
typical test. It is used for multiple choice tests most often, but it can be used on any test
that can be divided in half and scored consistently. Split-Half Reliability assumes that, if
a test is reliable, a student should score equally as well or poorly on two randomly
selected halves of the test.
1. Administer the test as you would normally. You will need to know how students
performed on the two randomly selected halves of the test, so it is important to
keep the responses each student gave for each question. A final score is not, in
itself, sufficient to complete the analysis.
2. Randomly divide the test into two parts. This is often done using an even-odd
approach. Each half of the test should approximately the same number of
questions. The questions in each half should be more or less equivalent. Essay
questions can be included as long as they are evenly distributed between halves
in terms of content and point value.
3. Score each half of the test for each student and record the scores in the
appropriate cells of the spreadsheet that can be accessed through the icon at the
bottom of this document. There is space for data from 50 students. If you have
fewer than 50 students you can leave those rows blank. In the example
spreadsheet, student 1 received a 47 on one half of the test and a 45 on the
other half.
4. The reliability coefficient will be automatically calculated. A reliability of 0.8 and
higher is generally considered to be good.
QUESTIONS AND ANSWERS
Q: How many students should I use for this statistic?
A: The statistic does take into account the number of scores that are used. Fewer
scores mean a lower likelihood of achieving good reliability. For the purposes of
technical skill assessment, you should strive to have at least one full class of students
(about 30). The spreadsheet will accommodate scores for up to 50 students.
Oregon Department of Education, March 2010
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Q: Can I use student scores from several classes or schools?
A: Yes, as long as you are using the same test and the method of administering the
test is equivalent.
Q: How long does the test have to be?
A: It is easier to demonstrate reliability as a test gets longer. The sample was
developed using a 100 point test. The test should be long enough to split into two
equivalent forms but short enough to be administered in the time provided for students.
Q: What data do you need for demonstration of reliability?
A: You can email a copy of the completed spreadsheet as proof of reliability.
Q: Should I use this on a performance assessment?
A: No, this is not appropriate for performance assessments or portfolios.
CONTACT
For additional information on Technical Skill Assessment, contact Tom Thompson at
tom.thompson@state.or.us or (503) 947-5790.
RESOURCES
SplitHalfReliability.xls
Oregon Department of Education, March 2010
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