Computer Examples--t Tests


1. Ho: Mu = a

A manufacturer of office furniture is designing a new computer table. Although it is known that the standard height for typing tables is 26" inches, the manufacturer is concerned that the best height for a computer might be different. A sample of n = 30 computer operators is obtained, and each is asked to position the height of an adjustable table at its most comfortable level. On the basis of this sample, should the company conclude that the best height for a computer table is different from 26 inches? Test with alpha equal .05.

Computer Program -- BMDP3D -- Data File = DESK
  /PROBLEM TITLE IS 'T-TEST - ONE SAMPLE'.
  /INPUT       VARIABLE IS 1.
               CASES ARE 30.
               FORMAT IS '(T3, F5.2)'.
               FILE = 'desk'.
  /VARIABLE    ADD IS 1.
               NAMES ARE HEIGHT,DIFF.
  /TRANSFORMATION DIFF = HEIGHT - 26.
  /TEST TITLE IS 'TEST FOR ZERO MEAN'.
               VARIABLE IS DIFF.
  /END
  /FINISH

2. Ho: mu-1 - mu-2 = 0 (Independent)

A researcher is interested in testing the opinions of college students concerning the value of their college education. She suspects that seniors will place more value on their education than will sophomores. A sample of 20 seniors and 20 sophomores is selected, and each subject is given an opinion questionnaire.

Computer Program -- BMDP3D -- Data File = OPINION
  /PROBLEM TITLE IS 'T-TEST FOR INDEP. SAMPLES'.
  /INPUT       VARIABLES ARE 2.
               CASES ARE 40.
               FORMAT IS '(F1.0,F3.0)'.
               FILE = 'opinion'.
  /VARIABLE    NAMES ARE CATEGORY, OPIN.
               GROUP IS CATEGORY.
  /GROUP       CODES (1) ARE 1, 2.
               NAMES (1) ARE SOPH,SR.
  /TEST        GROUPS ARE SOPH, SR.
  /END
  /FINISH

3. Ho: mu-1 - mu-2 = 0 (Dependent)

A researcher tests the effectiveness of a drug called Ritalin on hyperkinetic children. The researcher uses a sample of n = 12 hyperkinetic children ranging in age from 8 to 9 years of age. The children are told several brief stories. After each story, the experimenter asks the children questions about the story. The total number of questions answered correctly for all of the stories is recorded as the child's score. Because hyperkinetic children have attentional deficits, they should not perform well on this task when they are not treated. The researcher tests all of the children under two conditions: following administration of a sugar pill (placebo condition) and after receiving Ritalin. Determine if the drug treatment has an effect on performance. Use an alpha level of .01.

Computer Program -- BMDP3D -- Data File = HYPER
  /PROBLEM TITLE IS 'T-TEST FOR DEPENDENT SAMPLES'.
  /INPUT       VARIABLES ARE 2.
               CASES ARE 12.
               FORMAT IS '(T3,2F3.0)'.
               FILE = 'hyper'.
  /VARIABLE    ADD IS 1.
               NAMES ARE PLACEB,RITAL,DIFF.
  /TRANSFORMATION DIFF = PLACEB - RITAL.
  /TEST TITLE IS 'TEST FOR ZERO MEAN'.
               VARIABLE IS DIFF.
  /END
  /FINISH
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