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Experimental Methods and Design 2
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Post-Hoc Comparisons. Most liberal/conservativce?
Post-Hoc comparisons are comparisons run
after
data collection.
Number of possible comparisons c = (a)*(a-1) with a=# of groups. To determine
pairwise
comparisons just divide by 2
Fisher’s LSD (very liberal) -> Modified Bonferroni-> Bonferroni-> Tukey’s HSD (very conservative)
Familywise Error
The probability of at least one Type I error (a) for a set of many comparisons. aFW = (c)(a) with c= # of comparisons
“Fishing”
Conducting a large number of statistical tests, without theoretical reasons, and then “fishing” out the significant test results.
Calculating Fisher’s LSD
Anything greater than Fisher's LSD is significant.
T=
t=
A=
a=
AS=
s=
as=
[T]=
[A]=
[AS]=
T= Grand Total
t= # of grand totals (always 1)
A= Total for each condition
a= # of levels for the IV
AS= Individual scores
s= # of participants per condition
as= Total # of participants
[T]=T
^{2}
/as
[A]=(A
_{1}
^{2}
^{}
+A
_{2}
^{2}
)/s
[AS]=AS
^{2}
Planned Comparisons
Planned before the study is executed to test a specific hypothesis.
Only difference in how they are conducted is the alpha level used to determine significance.
Planned Comparisons: Rules for Creating Coefficients
There must be 1 coefficient for each mean
– Means not included in the comparison have a coefficient of zero
There is always two sets of means being compared
– means in the same set have the same sign (+ or -)
Coefficients must add to zero
Orthogonality
Orthogonal comparisons reflect independent or non-overlapping pieces of information.
The outcome of one comparison gives no indication whatsoever about the outcome of another orthogonal comparison.
Non-orthogonal contrasts can be hard to interpret.
What are the advantages of a Within-Subjects Design?
Control of individual differences (aka subject differences)
More likely to find an effect
Fewer participants needed
Efficiency gains (less time-consuming and expensive)…
Sequence effects
2) Carryover effects
a) Order
b) Practice
c) Interference
d) Differential
What confounds are specific to a Within-Subjects Design?
Confounds are extraneous variables that vary in some non-random way across conditions
1. Sequence
:– People change as they spend time working on tasks
– They can become bored, fatigued, or more excited.
2. Carryover:
– Responses to one condition influence the responses to a later condition
.– Different from sequence effects. Not the passage of time, but the impact of one condition on another.
2) Carryover effects
a) Order
b) Practice
c) Interference
d) Differential
Author
Arukio
ID
181616
Card Set
Experimental Methods and Design 2
Description
Notes for experimental methods and design test 2
Updated
2012-11-05T13:26:04Z
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