Experimental Methods and Design 2

  1. 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)
  2. 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
  3. “Fishing”
    Conducting a large number of statistical tests, without theoretical reasons, and then “fishing” out the significant test results.
  4. Calculating Fisher’s LSD
    • Image Upload 1
    • Anything greater than Fisher's LSD is significant.
  5. T=
    • 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]=T2/as
    • [A]=(A12+A22)/s
    • [AS]=AS2
  6. 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.
  7. 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
  8. 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.
  9. 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
  10. 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
Card Set
Experimental Methods and Design 2
Notes for experimental methods and design test 2