Single Factor Research

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Single Factor Research
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data Central tendency variablity correlation
Nominal   mode range phi
Ordinal   median range Spearman rho
Interval/ Ratio  Skewed   median range Convert to ranks Spearmans rho
Interval/ratio     mean Standard deviation Pearson r regression
 
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Type of design Parametric Non parametric
One sample Population sd known Z test none
One Sample Population sd unknown One sample t-test none
Two independent samples Independent t test Mann-Whitney U Rank sums test, one way chi-square
Two related samples Related (paired t test) Wilcoxon test
Three or more independent samples (1 factor) Between subjects ANOVA Post hoc test HSD or protected t Kruskal Wallis H Or one way chi squared Post hoc test Rank sums test
Three of more related samples ( 1 factor) Within subjects ANOVA Post hoc test HSD or protected t Friedman Post hoc Nemenyis test
 
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• If I want to test the efficacy of a new drug on
  blood pressure then I have some choices of
  design.

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• Two independent samples
• Control vs drug groups (random assignment)
• Comparison is independent t- test
• Or Mann -Whitney U

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• Non-equivalent groups
• Eg Sick vs Healthy
• Male vs female.
• Comparison is independent t- test
• Or Mann -Whitney U

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• Matched design.
• Pairs of twins sign up for study
• One twin is in control group the other in drug
  group
• Comparison is paired t-test
• Or Wilcoxon

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• Repeated design
• Take a baseline measure of BP for each subject
• Then give drug
• Repeated (paired) t-test
• Wilcoxon

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CONTROL GROUPS provide baseline for
comparison
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No treatment

• Compare treatment vs no treatment
• (no treatment only difference is variable of
  interest)
• Standard control for
• Situational
• Task or
• Instructional difference

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Placebo

• Standard for drug trials
• Or obvious clinical treatments
• Inert substance given for comparison
• Tests the protocol
• Tests the beliefs of treatment

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Waiting List

• If no treatment or placebo are unethical or not
  possible then assign subjects to waiting list.
• Must be done randomly (not first come first
  serve)

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Yoked

• Executive Monkey Experiment
• Two monkeys yoked together
• Executive controls off switch the other is
  helpless
• Both get shocked equally

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  No treatment Placebo Waiting List Yoked  
Perception of Treatment   none Believe treated Believe will be none
Beliefs effect Beliefs irrelevant Beliefs relevant Beliefs Relevant   Beliefs Irrelevant
  No treatment baseline   yes no yes yes
  IV - control yes yes yes Different amount of IV possible
 
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Only two levels

• Advantage
• Simple
• Direction of difference obvious
• Disadvantage
• Deceptive appearance of linearity
• Single hypothesis test