Hi,
Im stuck with a statistical question of one subchapter:
We have two groups surgeons versus non surgeons. We test the sensibility of the hand with wearing different size of gloves: fitted, undersized, oversized, and comparing them to bare hands (control).
Our questions are:
1) does glove fit alter the sensibility?
2) is sensibility of undersized gloves comparable to bare hand?
3) is there a difference in sensibility between surgeons and non surgeons when wearing gloves?
I believe that the control group=bare hands has to be excluded in the Two Way analysis, regarding to the question 1) and 3) since they require wearing gloves. Should the Question 2) analyzed separately with a one way ANOVA?
Thank you very much!
Yes, you should include your control group when doing any analysis because you will want to know if there is a difference between the control group and the experimental conditions. For example, you would have no way of knowing if having a bare hand is different than wearing an oversized glove. By including your control group it allows you to statistically determine if there is (or is not) a difference.
You could still use a two-way ANOVA with your questions, though. Here is what I would do (use your judgment for your own research)
1). Glove fit + surgeon status as predictor of sensitivity
This will give you a comparison of is a surgeon with no gloves has different sensitivity compare to non-surgeons who have over-fitted gloves, etc.
2). Will be taken care of in the above analysis. When you run your two-way ANOVA, be sure your analysis will report interaction effects and multiple comparisons.
3). This will also be taken care of in the first analysis.
A two-way ANOVA with interaction effects and multiple comparisons will report if there is a difference between surgeons and non-surgeons' sensitivity while wearing gloves of different thicknesses.
I hope this helps.
Two Way ANOVA should be encompassing all conditions for all questions.
Surgeon vs Non-surgeon X condition (no glove to over sized glove) is an appropriate interaction plot.
it is necessary to evaluate the sensitivity without gloves in all groups to determine threshold changes (establish a measurable baseline group).
Don't you have a repeated measures design? Then you should use rmANOVA or (better) a multilevel/hierarchical/mixed-effects model.
If for question 2 the differences between surgeons and non-surgeons in the glove-effect is of interest, you'd need a 2-way model. Otherwise you can also use a 1-way model (but then with all 4 "groups" to get a more robust estimate of the standard errors with more degrees of freedom).
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