Assumed knowledge
Francis & Howell
 Francis deals with power, effect sizes, confidence intervals and N
within each type of analysis as opposed to having a stand alone
section
 This makes it hard to review in Francis, but my suggestion is to
go through the pages listed in the Francis index for "effect sizes"
and "power"
 Howell is a little better, he has a chapter on Power (Ch15) but it
doesn't really deal with effect sizes and confidence intervals, and he
uses delta and gamma which he doesn't clearly link with commonly used effect
sizes such as d, r, etc. aargh!. So, read through Ch15, but concentrate on
the lecture/tutorial notes notes more so than with other topics so
far.
Downloadable files
Power

Use power.xls

If I am using a confidence interval of 95% and I want a power
level .8, what would be the minimum sample size to detect a
standardised mean difference of .3?

If I am using a confidence interval of 99% and I want a power level of
.7, what would be the minumum sample size to detect an effect size of
.7?

If I am using a confidence interval of 90% and I want a power level of
.9, with a sample size of 200, what effect size will I be able to
detect?

If I am using a confidence interval of 95% and I will have a sample
size of 50, and I want a power level of .8, what effect size will I be
able to detect?
Effect Sizes & Confidence Intervals with Cohen's d
 Use Cohensd.xls
 What is the effect size between two means (and how large is it?),
where M1 = 10, SD1 = 3, M2 = 12.5, SD2 = 4
 Using a 99% confidence interval, N = 20 in each group, is
this a significant difference?
 Using a 95% confidence interval, N = 20 in each group, is
this a significant difference?
 Using a 90% confidence interval, N = 20 in each group, is
this a significant difference?
 What happens if we increase the N in each group to 100?
 What is the effect size between two means (and how large is it?),
where M1 = 8, SD1 = 2, M2 = 3.5, SD2 = 2
 Using a 99% confidence interval, N = 40 in each group, is
this a significant difference?
 Using a 95% confidence interval, N = 40 in each group, is
this a significant difference?
 Using a 90% confidence interval, N = 40 in each group, is
this a significant difference?
 What happens if we decrease the N in each group to 10?
 What is the effect size between two means (and how large is it?),
where M1 = .5, SD 1= .1, M2 = .6, SD2 = .07
 Using a 99% confidence interval, N = 200 in each group,
is this a significant difference?
 Using a 95% confidence interval, N = 200 in each group,
is this a significant difference?
 Using a 90% confidence interval, N = 200 in each group,
is this a significant difference?
 What is the effect size between two means, N = 15, where M1
= 6.5, SD1 = 1, M2 = 7.5, SD2 = 1.1
 What is the confidence interval? Using only, the
confidence interval, is this difference significant?
 How large would N need to be to get a just significant
result?
 Using N = 15, how large would M2 need to be to get a just
significant result?
 It is possible to work the % of difference between two means, by
treating Cohen's d as a zscore in a normal distribution
Etasquared & Rsquared
 Use any dataset
 Design an analysis that can be tackled using MLR and ANOVA
 Obtain power (via the ANOVA analysis)
 Compare etasquared (from ANOVA) with R squared from MLR
 Compare partial etasquared (from ANOVA) with the beta
coefficients from MLR
 What can you conclude about the relationship between etasquared
and rsquared?
Error Bar Graphs
 Use any dataset
 Conduct a oneway ANOVA and graphically present the means and
confidence intervals using an Error Bar Graph  is this error bar
chart consistent with the statistical results?
 Conduct a twoway ANOVA and graphically present the means and
confidence intervals using an Error Bar Graph  is this error bar
chart consistent with the statistical results?
Summary of Metaanalysis
 Find a published metaanalysis
 Summarise the metaanalysis in 250 words
 Consider including:
 The research question
 The overall effect size and its size/significance  note which
type of effect size is used, commonly r or d
 Were there any predictors of the effect size, what were they, and
how important were they?
 Were there any other results of note (e.g, file drawer effect)?
 What were the strengths, limitations and/or recommendations of the
study?
 Include APA citation
 Note: There are no readings in the texts about metaanalysis, but
there's plenty on the web  suggest google search or this starting
point  Metaanalysis Research
Methodology
