Single Factor Research

data Central tendency

variablity correlation

Nominal 

mode range phi

Ordinal 

median range Spearman rho

Interval/Ratio  Skewed 

median range Convert to ranksSpearman’s rho

Interval/ratio  

mean Standard deviation

Pearson rregression

 

Type of design Parametric Non parametric

One sample Population sd known

Z test none

One SamplePopulation sd unknown

One sample t-test none

Two independent samples Independent t test Mann-Whitney URank sums test, one way chi-square

Two related samples Related (paired t test) Wilcoxon test

Three or more independentsamples (1 factor)

Between subjects ANOVAPost hoc test – HSD or protected t

Kruskal Wallis HOr one way chi squaredPost hoc testRank sums test

Three of more related samples ( 1 factor) Within subjects ANOVAPost hoc test –HSD or protected t

Friedman Post hocNemenyi’s test

• If I want to test the efficacy of a new drug on blood pressure then I have some choices of design….

• Two independent samples

• Control vs drug groups (random assignment)

• Comparison is independent t- test

• Or Mann -Whitney U

• Non-equivalent groups

• Eg Sick vs Healthy

• Male vs female….

• Comparison is independent t- test

• Or Mann -Whitney U

• 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

• Repeated design

• Take a baseline measure of BP for each subject

• Then give drug

• Repeated (paired) t-test• Wilcoxon

CONTROL GROUPS –

provide baseline for comparison

No treatment

• Compare treatment vs no treatment• (no treatment only difference is variable of

interest)

Standard control for :• Situational • Task or • Instructional difference

Placebo

• Standard for drug trials

• Or obvious clinical treatments

• Inert substance given for comparison

• Tests the protocol

• Tests the beliefs of treatment

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)

Yoked

• Executive Monkey Experiment

• Two monkeys ‘yoked’ together

• Executive controls off switch the other is helpless

• Both get shocked equally

   

  No treatment

Placebo Waiting List Yoked 

Perception of Treatment 

none Believe treated

Believe will be

none

Beliefseffect

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

Only two levels

Advantage

• Simple

• Direction of difference obvious

Disadvantage

• Deceptive appearance of linearity

• Single hypothesis test