Download Slide 1

Single Factor Research
data
Central
tendency
variablity
correlation
Nominal
mode
range
phi
Ordinal
median
range
Spearman rho
Interval/
Ratio
Skewed
median
range
Convert to
ranks
Spearman’s
rho
Interval/ratio
mean
Standard
deviation
Pearson r
regression
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
Nemenyi’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
Beliefs
effect
Beliefs
irrelevant
Beliefs
relevant
Beliefs
Relevant
Beliefs
Irrelevant
yes
no
yes
yes
yes
yes
yes
Different
amount of
IV
possible
No
treatment
baseline
IV - control
Only two levels
Advantage
• Simple
• Direction of difference obvious
Disadvantage
• Deceptive appearance of linearity
• Single hypothesis test