Greetings, what is the estimated sample size for the hierarchical multiple regression analysis with 2 variables entered in the first step and one additional variable entered in the second step. Alpha=.05, power= .80, medium effect size?
Dear Ahmad,
there are web calculator for sample sizes:
A Rough Rule of Thumb
In terms of very rough rules of thumb within the typical context of observational psychological studies involving things like ability tests, attitude scales, personality measures, and so forth, I sometimes think of:
n=100 as adequate
n=200 as good
n=400+ as great
These rules of thumb are grounded in the 95% confidence intervals associated with correlations at these respective levels and the degree of precision that I'd like to theoretically understand the relations of interest.
http://stats.stackexchange.com/questions/10079/rules-of-thumb-for-minimum-sample-size-for-multiple-regression
Article When the hypothesis is invalidated, does it matter? A new ap...
http://www.danielsoper.com/statcalc/calculator.aspx?id=16
Someone sent me this link :)
Dear Ahmad
Sample size depends on standard deviation ( from previous studies ) and the margin of error you decided .
G*Power software is effective tool to calculate sample size for many ranges of experiments. Also, you can determine effect size and power of the test, G*Power is free to download and easy to use after reading the manual, the download link:
http://download.cnet.com/G-Power/3000-2054_4-10647044.html
The link to download G*Power manual:
http://www.gpower.hhu.de/fileadmin/redaktion/Fakultaeten/Mathematisch-Naturwissenschaftliche_Fakultaet/Psychologie/AAP/gpower/GPowerManual.pdf
I hope this information be helpful for you
Good Luck
I am struggling to figure out how many participants I need for my quantitative study. If I have 8 variables, how many participants do I need?
Dear Elizabeth
Please let me know the purpose of your study and the data analysis test so that I can calculate it for you using the G power
Perfect, Ahmad.
The purpose of my study is to examine the relationship between posttraumatic growth and body image among women who have experienced childhood sexual abuse (CSA). the present research will aim to determine the relationship between PTG and positive and negative body image attitudes. Specifically, the researcher will explore the level of severity related to the CSA occurrence and determine if severity impacts body image. Additionally, I will examine whether or not severity sufficiently serve as covariate for examining the relationship between body image and PTG outcomes. Finally, I will determine the correlation between the five subscales of the Posttraumtic Growth Inventory measure and positive and negative body image.I will use two measures of body image (Body Appreciation Scale-2 and Body Attitude Test). I will use a hierarchical regression model.
Thank you, Béatrice Marianne Ewalds-Kvist
Ahmad, your thoughts?
If you use regression analysis you can use a thumb rule
8 x 10 = 80, then you can have some extra because some will drop out
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