Dependent t test
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Dependent samples t
-the dependent variable is measured two or more times for each individual in a single sample
What are dependent samples?
-Scores in one group are related to scores in another group
How do we get dependent samples
1.
2.
-When you measure the same people more than once (repeated measures)
-Matched samples (someone in sample A is paired with someone in sample B) and they are identical on some measurements
Repeated Measures design
1.
2.
-Each subject is measured more than once in your study
-You have one sample of people, but they provide two or more samples of data
Matched Samples Design
-Two or more samples of people that provide one sample of data each
-People matched to each other in pairs
-Treated as though they are one sample
-Often used in quasi-experiments when you can't randomly assign people to conditions
All statistics are done with
Difference scores (d=x2-x1)
What test do we use?
1 sample t
Mean difference formula
see chart
H0
u
_{D=0}
Standard error dependent t test
See chart
Sum of squares D
Variance D
see chart
Cohen's D for mean difference
-Mean difference in standard deviation units
Benefits of Repeated measures
1.
2.
3.
-Reduces error due to individual differences
-Reduces number of participants
-Can observe changes over time (longitudinal studies)
Carryover effects
-The first treatment or measurement influences scores on the second measurement
Progressive error
-Passage of time alone can produce change
Solutions to carryover and progressive error
1.
2.
-Counterbalance order of treatment
-Choose a different research design
Assumptions of related-samples t-test
1.
2.
Observations within each treatment are independent
Population distribution of difference scores must be approximately normal
Card Set Information
Author:
Trekofstarsx
ID:
298422
Filename:
Dependent t test
Updated:
2015-03-15 04:26:06
Tags:
test
Folders:
t test
Description:
Dependent sample t test
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