T-Tests and Likert scales

 

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*I've tried a few experiments making Likert scales from normal variates, and
	seeing whether there was any difference in t-tests.  The result: not much
	difference.  The syntax below was what I used.  It's set up to make normal
	variates with a SD of 3 (but you could change that) and means ranging from
	0.5 to 5.5; then "Likertize" them by rounding to the nearest point of a
	1-to-5 scale.
* Posted by Ted Drawneek to SPSSX-L on 2001/09/22.

-----START OF SYNTAX-----
* Make data file with 3300 cases.
data list list /v1 to v3300.
begin data

end data
flip.
* Make 1..11 grouping variable.
compute group=trunc(($casenum-1)/300)+1.
* Make 11 normal variates of SD=3, with means of 0.5 .. 5.5.
compute normal=rv.normal(group/2,3).
* Make Likert scales.
compute likert=rnd(normal).
if likert<1 likert=1.
if likert>5 likert=5.
* t-tests of adjacent groups.
T-TEST  GROUPS=group(1 2)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(2 3)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(3 4)  /VARIABLES=normal likert .
T-TEST  GROUPS=group(4 5)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(5 6)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(6 7)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(7 8)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(8 9)  /VARIABLES=normal likert .
T-TEST  GROUPS=group(9 10)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(10 11)  /VARIABLES=normal likert.
* t-tests of  groups 2 apart.
T-TEST  GROUPS=group(1 3)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(2 4)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(3 5)  /VARIABLES=normal likert .
T-TEST  GROUPS=group(4 6)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(5 7)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(6 8)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(7 9)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(8 10)  /VARIABLES=normal likert .
T-TEST  GROUPS=group(9 11)  /VARIABLES=normal likert.
* t-tests of  groups 3 apart.
T-TEST  GROUPS=group(1 4)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(2 5)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(3 6)  /VARIABLES=normal likert .
T-TEST  GROUPS=group(4 7)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(5 8)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(6 9)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(7 10)  /VARIABLES=normal likert.
T-TEST  GROUPS=group(8 11)  /VARIABLES=normal likert .
* Table of Frequencies.
TABLES
  /FORMAT BLANK MISSING('.') /TABLES
  (LABELS)  BY
  group > likert
  /STATISTICS COUNT ((F5.0) 'Count' ) .
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