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Thread: Power and Sample Size Calculation

  1. #1
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    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. #2
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    Karabiner's Avatar
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    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


  3. #3
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    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.

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