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Lecture 17

PSYC 210 Lecture Notes - Lecture 17: Level Of Measurement, Standard Deviation, Test Statistic


Department
Psychology
Course Code
PSYC 210
Professor
Snjezana Huerta
Lecture
17

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Ѱ 210 Hypothesis Test examples
independent t test with homogeneity of variance
Snjezana.Huerta@sfu.ca
Does the level of academic achievement differ for first-born children who are daughters and
first-born children who are sons in Canadian families? (Assume that academic achievement is
normally distributed in both populations and that we are measuring it using an interval scale of
measurement.) Data were collected from 10 randomly-selected first-born daughters and 10
randomly-selected first-born sons. Use an alpha of .01.
Step 1: Specify the Parent Populations.
X
1
~
where 1 = first-born daughters
X
2
~
where 2 = first-born sons
Scale of measurement: ____________
Assumptions to be tested:
Normality of the distribution of the X
1
scores
Normality of the distribution of the X
2
scores
Homogeneity of variance (i.e.,
22
2
2
1X
σσσ
==
)
Step 2: Specify hypotheses.
H
0
:
H
1
:
Step 3: Specify the test statistic and the null distribution.
21
)(
21
XX
s
cXX
t
=
~
t
(
n
1
+
n
2
-
2
) n
1
= number of first-born daughters, n
2
= the number of first-born sons
(
)
==Ε
21
21 XX
XX
µ
n =
+=
21
211
21
nn
ss p
XX
calculated after collect data
Step 4: Specify decision rule(s).
α = _____; ____-tailed test;
df = _____________________________;
critical value(s): ________________________
*Collect data (using random sampling) & conduct thorough descriptive analyses
(see p. 2)
Step 5: Calculate test statistic.
+=
21
211
21
nn
ss p
XX
21
)(
21
XX
obs
s
cXX
t
=
Step 6: Make a decision re: H
0
.
t
obs
t
crit
21
XX
µ
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