Rich Ulrich <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>... > 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?
It is indeed three growth curves of the same organism . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
