Effect size basics
Displays the relationship between variables or the difference between groups is
What is effect size?
measures the size of the difference between two groups
What does Cohen’s d measure?
emphasizing the size of effect promotes a more scientific approach, as unlike significance tests, effect size is independent of sample size
Why should we report the effect size?
By performing a power analysis
How can we use a set effect size and significance level to determine the sample size needed for a certain power level?
The effect size of the population can be known by dividing the two population mean differences by their standard deviation.
How can you find the standardized mean difference?
It indicates the practical significance of a research outcome
What does effect size tell us?
measures the strength of the relationship between two variables
What does Pearson’s r measure?
tells us that an intervention works, whereas an effect size tells us how much it works
What is one difference between p-value and effect sizes?
Effect Sizes
What is known as the raw data in meta-analysis studies because they are standardized and easy to compare?
r = correlation coefficient
N = number of pairs of scores
∑xy = sum of the products of paired scores
∑x = sum of x scores
∑y = sum of y scores
∑x2= sum of squared x scores
∑y2= sum of squared y scores
What do the Pearson r correlation variables stand for
indicates limited practical applications
What does a small effect size mean?
takes the difference between two means and expresses it in standard deviation units to tell you how many standard deviations lie between the two means
How does Cohen do work?
Standardized mean difference, odd ratio, and correlation coefficient
In what three ways can effect size be measured?
Knowing the expected effect size means
You can figure out the minimum sample size you need for enough statistical power to detect an effect of that size?
p-values and effect sizes
Statistical significance is denoted by what? whereas practical significance is represented by?
means that a research finding has practical significance
What does a large effect size mean?
depends on your research design
How do you identify what standard deviation to use?
For instance, if we have data on the height of men and women and we notice that, on average, men are taller than women, the difference between the height of men and the height of women is known as the effect size.
Give an example of what effect size is intended for
Effect Sizes and significance level
What two things are needed to determine sample size for a certain power level?
efers to the likelihood of a hypothesis test detecting a true effect if there is one
What is statistical power?
shows that an effect exists in a study vs. shows that the effect is large enough to be meaningful in the real world.
What is the difference between statistical and practical significance?
The formula is rather complex, so it’s best to use a statistical software to calculate
How do you make calculations with Paerson’s r?
The greater the effect size, the greater the height difference between men and women will be
In the previous example, what does a greater effect size mean?
calculate effect sizes
before you begin your study as well as after you complete data collection its helpful to what?
the best statistic to measure the effect size for nominal data
What is Chi-square?