I'm currently working on my under-grad dissertation project, researching whether Raffinose impacts gut barrier function. I have used a control measure and a high, medium and low dose of Raffinose treatment, and tested on Caco-2 cells over a period of 4, 24 and 48 hours. Would I need to use a one-way onova or a two-way onova?
You have two independent variables (dosage level and exposure period), so you need to do a 2-way ANOVA.
You have two independent variables (dosage level and exposure period), so you need to do a 2-way ANOVA.
A two way anova is the most common and classical treatment for such type of data.
Nevertheless, my own experience is that, _ if the observed response is monotonic(*)_, a more powerful method is available : multiple regression with, as independent variables : dose, time and dose:time interaction, the latter being the mere product of the two former - and this interaction is the question at stake for comparing treatments.
Don't bother if you do not have a quantitative value precisely attached to the IV, a set of values such that : 1, 2, 3, etc will do.
(*) of the outermost importance, can be easily checked graphically . If the response is not monotonic, the use of the ordered nature of your IV is still possible but more technical - see a chartered statistician.
ANOVA and regression are identical at an arithmetical level. So, the interaction effect you get from a product term in regression will give you the same results as examining the equivalent set of group means in ANOVA.
to David L. Morgan - you shoul check the df of anova and the df of multiple regression.
They are the same. All it takes is a little bit of algebra to convert the formulas for ANOVA into dummy-variable regression.
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