mcnemar's test
DESCRIPTION
I had prepared and presented this as my report for MLS 602 (Statistics in Library and Information Science), one of the core subjects I have taken when I started Master in Library and Information Science at my alma mater, Polytechnic University of the Philippines. McNemar's Test is a non-parametric method used on nominal data. It is applied to 2 × 2 contingency tables with a dichotomous trait, with matched pairs of subjects, to determine whether the row and column marginal frequencies are equal ("marginal homogeneity"). It is named after Quinn McNemar, who introduced it in 1947.TRANSCRIPT
McNemar'sTest
Nestor D. Mores, Jr.Pamantasan ng Lungsod ng Marikina
McNemar'sTest
- is a non-parametric method used on nominal data. It is applied to 2 × 2 contingency tables with a dichotomous trait, with matched pairs of subjects, to determine whether the row and column marginal frequencies are equal ("marginal homogeneity"). It is named after Quinn McNemar, who introduced it in 1947.
(Answers.com, 2011)
McNemar'sTest
- is particularly useful in “before and after” designs (e.g., change in attitudes regarding unionization).- is also used for testing for an association in a 2 x 2 table when the samples are matched according to one or more variables like age, sex, weight, IQ and others.
APPLICATIONS:
McNemar'sTest
The McNemar’s test corrected for continuity (Everitt, 1976) which has a chi-square distribution with one degree of freedom is:
McNemar'sTest
The letters a, b, c, and d stands for the frequencies in the four cells as illustrated in the following example.
CELL
S a
& b
ARE
THE
ONES
OF
INTE
REST
THE TEST DETERMINES WHETHER THE FREQUENCY IN CELL a DIFFERS SIGNIFICANTLY FROM THE
FREQUENCY IN CELL d. IN OTHER WORDS, IT TESTS WHETHER THERE IS A SIGNIFICANT DIFFERENCE IN
THE NO. OF STUDENTS WHO FAILED TEST A BUT PASSED TEST B AND VICE VERSA.
McNemar'sTest
A random sample of 210 college instructors were asked if they were in favor of forming a faculty union before & after attending an open discussion on the pros & cons of faculty unionization. The obtained frequencies are presented in the following table. Test whether the lecture caused a significant change in the instructors’ stand regarding the issue.
EXAMPLE:
McNemar'sTest
Applying McNemar’s formula
TO TEST FOR THE SIGNIFICANCE OF THE OBTAINED VALUE, WE LOOK AT THE CHI-SQUARE
DISTRIBUTION UNDER 1 df. THE COMPUTED VALUE EXCEEDS THE TABULAR VALUE OF 6.63 FOR SIGNIFICANCE AT THE .01 LEVEL. IT IS ALSO
GREATER THAN THE TABULAR VALUE AT THE .005 LEVEL WHICH IS 7.88. THUS, WE CONCLUDE THAT THE LECTURE CAUSED A SIGNIFICANT CHANGE IN THE INSTRUCTORS’ STAND REGARDING A FACULTY
UNION.
McNemar'sTest
References: McNemar, Quinn (June 18, 1947). "Note on the sampling error of the difference between correlated proportions or percentages". Psychometrika 12 (2): 153–157. Reyes, Flordeliza C. Applied Basic Statistics (1996)
McNemar'sTest
Thank you.