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Power Analysis - Lab Exercises
Exercise 1: Power Analysis
- Examine the data contained in BodyMeasures.txt.
The file lists a series of measures for individual brain structures in
range of African Great Lake Cichlids. A description of the data set is
- What is the effect size for differences in standard length (STDL)
between individuals from the lakes Victoria and Malawi
- You have just finished collecting data from an awesome, nifty,
schnazzy, wickedly cool experiment you designed. You know that it is
true, and you will gladly demonstrate, that "acupuncture gives pain
relief right after finishing a 30 minute treatment". The effect size,
measures as the average magnitude of the improvement in pain scores for
someone who undergoes acupuncture, is a standardized mean difference
(SMD, Cohen's d) of -0.61. You measure pain before and after the
treatment on a point scale for physical pain. The pain scale asks "How
much pain do you feel, on a scale of 1-10?"
- You know you want to conduct the analysis with a criterion for
rejecting your null hypothesis set at p = 0.01 and you want to ensured
that you had at least a 70% chance of detecting this as a treatment
effect, if it really existed. How many individuals would you have to
include to match these conditions.
- Your associate beat you already to it and she already measured
changes in pain levels in 5 individuals between before and after. What
are her chances of detecting the effect at a p level of 0.05?
- What would he effect size have to be minimally to detect the effect
in 5 individuals and p=0.05 and a power of 0.9?
- Why might one argue that "low" power is incompatible with doing
last modified: 02/18/01[an error occurred while processing this directive]