Hallo! I have data of the following design: N subjects were measured at Baseline (visit 1) and at 3 following time points (visit 2-4). There is or is not a treatment. Say, the results of visits 1 to 4 are Y1, Y2, Y3, Y4.
T: Variable Treatment (yes/no) V: Variable Visit (2, 3, 4 - without baseline) id: Variable subject identification number N: number of subjects Most interesting is the question if there is a difference in treatment between the results of visit 4 and baseline. (The other time points are also of interest.) I am thinking of different possibilities for the analysis (balanced design): 1) ANOVA with differences to baseline without patient effect Let YD be the differences to baseline (Y2-Y1, Y3-Y1, Y4-Y1). The model will be: YD ~ T + V + T*V + E Var DF Meaning T 1 Treatment V 2 Visit (2-4) T*V 2 Interaction E 3*N-1-5 Error 2) ANOVA with differences to baseline with patient effect Let YD be the differences to baseline (Y2-Y1, Y3-Y1, Y4-Y1). The model will be: YD ~ T + V + T*V + id[T] + E (E: Error) Var DF Meaning T 1 Treatment V 2 Visit (2-4) T*V 2 Interaction id[T] N-2 subjects nested under T E 3*N-1-(N-2)-5 Error (if size of both treatment groups equal) 3) ANCOVA without patient effect Let Y be the values at visit 2-4 (Y2, Y3, Y4). The model will be: Y ~ T + V + T*V + Y1 + E Var DF Meaning T 1 Treatment V 2 Visit (2-4) T*V 2 Interaction Y1 1 baseline T*Y1 1 Interaction E 3*N-1-7 Error 4) ANCOVA with patient effect Let Y be the values at visit 2-4 (Y2, Y3, Y4). The model will be: Y ~ T + V + T*V + Y1 + id[T] + E (E: Error) Var DF Meaning T 1 Treatment V 2 Visit (2-4) T*V 2 Interaction Y1 1 baseline id[T] N-2 subjects nested under T E 3*N-1-7 Error witout intercept! (with intercept I get singularities) (Interaction T*Y1 Interaction is not possible) 5) t-test with difference to baselne (visit 4 minus visit 1, Y4-Y1, group by treatment T) So I can think different possibilities to analyse the data. WHAT'S BEST??? Hope somebody can help! Karl . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
