On 4 Mar 2004 08:28:34 -0800, [EMAIL PROTECTED] (Euh) wrote: > Hi all, > > I'm following the time course of a certain variable by using three > independent measurement techniques (for which I can estimate the > variance associated with the measurment) > > I can't really assume any function to describ the evolution of the > variable over time (linear, quadratic, etc). Is there a way to compare > the results and assess if all the methods give similar results ? > > ANOVA analysis at each time ? > > An example would be: > > Method 1 Method 2 Method 3 > mean stdev mean stdev mean stdev > t1 24.6 6.4 31.0 13.8 15.5 5.7 > t2 123.5 87.6 155.2 71.5 62.3 20.0 > t3 174.0 33.8 142.7 46.4 75.8 18.9 > t4 210.6 91.2 113.6 26.8 101.9 45.1 > t5 396.4 25.4 263.9 16.5 209.3 11.7 > t6 303.7 66.7 271.9 156.6 216.9 172.1 > t7 153.6 93.4 261.0 225.6 76.0 41.7 > t8 250.9 140.7 289.5 122.7 93.7 28.1
Preliminary points: There is an enormous range in means with an apparent zero-minimum, and a huge increase in variance for larger numbers. This strongly suggests the matter of a reliability model would be helped, most likely, by taking the log of each of the scores. The huge variation of variances also implies (I hope) that those variances are based on 2 or 3 observations at most; the numbers are not individually precise. Here are evolutions over time: Is there any component of time-series correlation for the multiple measurements of each method? Is there a *strong* component? Did someone say these are animal experiments? - that's what comes to my mind, and it gives me something concrete to discuss - You should try to use the within-animal correlation, if there is one, to improve the estimates, or to improve the knowledge of the *variance* of the estimates. I mean, there are at least two measures of Method-One at t4, t5, and t6, and they show an increase, then decrease, in means. Is this describing a biological reality of a *trend*, or is this 'sampling variability' between different specimens? - *antibody* levels may be tapped week after week, and there may be strong correlation within-animal. However, if measures require 'sacrificing' an animal in order to measure some organ, the weekly scores do not have this component. Do the scores reflect 8weeks times 3 times 3 = 72 animals, or do they reflect just 3 times 3 animals, each measured 8 times? By the way, *are* those similar results, according to clinical judgment? -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html - I need a new job, after March 31. Openings? - . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
