# Thread: Power and Sample Size Calculation

1. ## Power and Sample Size Calculation

Hi, First post here--i'm having trouble figuring out how to calculate the sample size for a study I'm planning. I don't have much statistics background, so bear with me--

My guess is that I should be doing a "One Way ANOVA Power analysis?"

Here is my hypothetical example:
I'm looking at backpack strap thickness, and the relationship with the backpack breaking.
-All other variables controlled for--only looking at thickness and breakage.
-There are 3 different thicknesses of backpack straps (1", 2", 3" thick).
-Backpack breaking is an all-or-none event.

How many backpacks do I need to test in each group?

Based one similar studies, I have the breakage rates of 1"=20%; 2"=25%; 3"=14%. Am I doing the right test? I'm not sure how I plug in the breakage rates.

2. ## Re: Power and Sample Size Calculation

This is not for an ANOVA, since interval scaled variables are nowhere involved.
You could perform a Mann-Whitney U-test using break yes/no as grouping variable
and thickness as ordinal scaled dependent variable. Or, you could treat thickness as
categorical variable and perform a Chi² test.

With kind regards

K.

3. ## Re: Power and Sample Size Calculation

The one way ANOVA only allows for continuous outcomes. Here, you have a binary one. If you want associative go chi square, if you want predictive, go with logistic regression.

 Tweet

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts