Path: janda.org/c10
> Overview
of SPSS
>
Analyze
>
TTest

Statistical
Package
for the
Social
Sciences
Syntax for TTEST Command

TTest
Use the TTEST procedure to test for a
statistically significant difference in means
between two groups. The TTEST computes a
tvalue which is a standardized score, similar to a
zscore.
The tvalue is calculated by dividing the difference
in means between the groups by the standard error of the
sampling difference between means. Remember that
the "standard error" of a statistic (the statistic here
is the value of the difference between the means) is just
another name for the standard deviation of the sampling
distribution for that statistic. The syntax for the most
common TTEST command is as follows:

TTEST

The "groupvar" is the name of the variable used to
create the two groups being compared. For example, "Region"
might be the variable that furnishes the groups.
(n1,n2) indicates the two values of the groups being
compared. To compare European nations with African nations
in the POLITY dataset, specify (2,6).
variable is the name of the variable to analyze for
difference of means. Suppose that you wanted to compare
European nations with African nations for the percent of
land under cultivation. The name of the variable in the
POLITY data would be landcult.
REGION seven world regions (POLITY dataset)
Valid Cum
Value Label Value Frequency Percent Percent Percent
ANGLOAMERICAN 1 5 4.5 4.5 4.5
EUROPEAN 2 17 15.3 15.3 19.8
LATIN AMERICAN 3 23 20.7 20.7 40.5
ASIA 4 15 13.5 13.5 54.1
MIDDLE EAST 5 11 9.9 9.9 64.0
AFRICA 6 32 28.8 28.8 92.8
EASTERN EUROPE 7 8 7.2 7.2 100.0
  
Total 111 100.0 100.0


GROUPS =
groupvar
(n1,n2) /
VARIABLES =
variable

TTEST output

 2 ttest groups=
region (2,6) variables=landcult.
ttests
for Independent Samples of REGION
seven world regions

Variable

Number
of Cases

Mean

SD

SE of Mean


LANDCULT % OF
LAND UNDER ACTUAL CULTIVATION

EUROPE

16

29.0000

17.588

4.397


AFRICA

31

11.1065

10.988

1.974


Mean Difference =
17.8935
Levene's Test for Equality of Variances:
F= 5.620 P=
.022
ttest for
Equality of Means 95%

Variances

tvalue

df

2Tail Sig.

SE of
Diff

CI for
Diff

Equal

4.29

45

.000

4.171

(9.493,
26.295)













df 2Tail
Sig

. . 45 .000
Unequal . 3.71 . 21.22
.001 4.820 (7.877, 27.910)

