ES Bootstrap: Correlated Groups
Directions for UseIntroduction
ES Bootstrap: Correlated Groups is a windows-based program that provides Bootstrapped
confidence intervals for four variations of Cohen’s d measure of effect size. These fourvariations include:
Y1 − Y2

Pooled estimator:δˆ =Pooled robust estimator:δˆR = 0.642 ⎢( S12 + S 22 ) / 2

⎡

(1)

⎤⎥
⎢⎣ ( S w21 + S w2 2 ) / 2 ⎥⎦Yt1 − Yt 2(2)Nonpooled estimator:δˆ j =

Y1 − Y2Sj(3)⎡Y − Y ⎤Nonpooled robust estimator: δˆRj = 0.642 ⎢ t1 t 2 ⎥⎣⎢ S wj ⎦⎥(4)

Formatting Data for Import
The imported data file must contain only numeric entries, and be in text format (have a“.txt” extension). Each row of the text file corresponds to a case, and each column
corresponds to a variable. One of three different delimiters may be used to delineate thevariables in the data base: a space, a comma, or a tab. For example, if our data fileconsists of three cases and five variables, then the data file could be space-delimited:1 1 1 1 12 2 2 2 23 3 3 3 3
Or comma-delimited:
1,1,1,1,1
2,2,2,2,2
3,3,3,3,3

Directions for Using ES Bootstrap: Correlated Groups1

Or tab-delimited:123123123123123

The same delimiter must be used throughout the data file. In addition, the data must
begin in the first row. As a result, variable names should not be included in the data file
to be imported. ES Bootstrap will identify variables by their column placement.
ES Bootstrap can read in up to 100 variables and 10,000 cases. Two One of the variables
must correspond to the repeated measurements under investigation, given by Y1, and Y2 inEquations 1, 2, 3, and 4 above.
Importing Data
The top portion of the main window of ES Bootstrap is devoted to importing the data file.
To import the data:(A) Specify the type of formatting used in delimiting the data file in the box on the far
left-hand side of the Main Window called “Type of Delimiter”. Three options areprovided: space-delimited, comma-delimited, and tab-delimited. The default
setting is space-delimited. If the appropriate type of delimiter is not provided, thedata will not be read in.
(B) Specify the directory (drive and folder) and the file name of the data file to beimported.
(C) Click the “Import Selected Data File” button towards the right-hand side of theMain Window. Upon clicking the “Import Selected Data File” button, a message
should appear in the Output Window that specifies the path of the selected file,the number of cases, and the number of variables.
For example, the message might look like:
Opened the text file: C:\Analysis\Data100.txt
Number of Cases: 200
Number of Variables: 2Running Descriptive Analyses
To obtain descriptive statistics for each variable (e.g., mean, standard deviation, etc.),
select “Descriptives” from the Analyses Menu, and the select all desired variables. Theresults will be printed in the Output Window.
Construct Bootstrapped Confidence Intervals

Directions for Using ES Bootstrap: Correlated Groups2

To obtain bootstrapped confidence intervals for each of the four variations of the effectsize estimator, do the following:(A) Select “Effect Size Bootstrap” from the Analyses Menu. This will result in theappearance of the Effect Size Bootstrap Window.
(B) Select the first level of the repeated measure (Y1) in the “Pick Variable 1” list.
(C) Select the second level of the repeated measure (Y2) in the “Pick Variable 2” list.
(D) Select the number of bootstrap trials (from 600 to 2000). The current trial number
will be displayed in the “Trial number” box during the analysis.
(E) Select the level of confidence desired (90%, 95%, 99%).
For example, running the bootstrapped confidence intervals with 600 trials and a 95%
confidence interval yields the following output:
GROUP-LEVEL STATISTICS--------------------------------------------StatisticVar 1Var 2--------------------------------------------Sample Size
5050
Mean
Trimmed Mean

4.5
4.433

5.62
5.9

Variance
7.969
10.771
Wins. Var.
6.988
7.992
--------------------------------------------Var1 = Var 2; Var2 = Var 1

EFFECT SIZE ESTIMATES AND 95% CI-------------------------------------------------Pooled variance = 9.37
Pooled Winsorized variance = 7.49
Pooled Cohen's D = 0.366
Pooled Robust Cohen's D = 0.344
Nonpooled Cohen's D = 0.397
Nonpooled Robust Cohen's D = 0.357
95% CI for population pooled D = (0.181, 0.565)
95% CI for population pooled Robust D = (0.154, 0.578)
95% CI for population nonpooled D = (0.197, 0.597)
95% CI for population nonpooled Robust D = (0.174, 0.632)-------------------------------------------------Nonpooled variance obtained from Varaible 2
Number of attempted bootstrap trials = 600
Number of valid pooled D bootstrap trials = 600
Number of valid pooled robust D bootstrap trials = 600
Number of valid nonpooled D bootstrap trials = 600
Number of valid nonpooled robust D bootstrap trials = 600

Directions for Using ES Bootstrap: Correlated Groups3Note that the appearance of “9999999” for any of the statistics values indicates that thestatistic could not be computed (usually due to lack of variance).
Save Output
To save the contents of the Output Window, select “Save Output” from the File Menu. A
window will appear that will permit you to select the directory where you wish to savethe output. The output file will be saved as a text document (with extension “.txt”).
Open Output
You may open the output of a previous ES Bootstrap session in the Output Window ofES Bootstrap by selecting “Open Output” from the File Menu. Note that opening anoutput file in ES Bootstrap will cause any output currently in the Output Window to be
replaced by the contents of the opened file.

Directions for Using ES Bootstrap: Correlated Groups4