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RE: st: R: which statistics to use


From   "b. water" <barleywater@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: R: which statistics to use
Date   Wed, 24 Mar 2010 00:42:40 +0000

dear Carlos,
 
Thank you for your advice. I'll give this a go.
 
bw
 
 

> From: carlo.lazzaro@tiscalinet.it
> To: statalist@hsphsun2.harvard.edu
> CC: barleywater@hotmail.com
> Subject: st: R: which statistics to use
> Date: Mon, 22 Mar 2010 10:41:13 +0100
> 
> Dear b,
> Though I am not sure if I am reading your data correctly (due to plain text
> format), I would suggest an OLS with clustered standard error:
> ................begin example...................................
> set obs 12
> input concentration sample condition time id
> .2 1 1 0 1
> .3 1 1 1 2
> .3 1 1 2 3
> .2 2 1 0 4
> .5 2 1 1 5
> .9 2 1 2 6
> .7 1 2 0 1
> .7 1 2 1 2
> .9 1 2 2 3
> .7 2 2 0 4
> 1.02 2 2 1 5
> 1.03 2 2 2 6
> end
> regress concentration sample condition time, robust cluster(id) 
> Dr. Carlo Lazzaro
> 
> Studio di economia sanitaria
> 
> Via Stefanardo da Vimercate, 19
> 
> 20128 Milano
> 
> tel/fax: 02 26000516
> 
> portatile: 335 6786741
> 
> e-mail: carlo.lazzaro@tin.it
> 
> carlo.lazzaro@tiscalinet.it
> 
> -----Messaggio originale-----
> Da: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di b. water
> Inviato: lunedì 22 marzo 2010 3.03
> A: statalist@hsphsun2.harvard.edu
> Oggetto: st: which statistics to use
> 
> Dear all,
> 
> Stata 8.2,
> 
> I have data consisting of serum concentrations measured at regular intervals
> but under two different conditions (but a few missing reading here and
> there) like so:
> 
> 
> condition_1 condition_2
> t0 t1 t2 t0 t1 t2
> sample_1 0.2 0.3 0.3 0.2 0.5 0.9
> sample_2 0.7 0.7 0.9 0.7 1.2 1.3
> .
> .
> .
> .
> .
> .
> sample_n 0.3 0.5 0.6 0.3 0.8 1.1
> 
> Just 'eye-balling' the data I can see that condition_2 did affect the
> concentrations. My questions:
> 
> 1. How may I show that in condition_1 concentration at t1 and t2 _are_
> statistically different from t0 (if indeed they are). Had it been just t0
> with one other time interval, I would have thought of paired t-test off the
> bat but don't what to do in this circumstances. It looks like ANOVA but
> again would appreciate advice.
> 
> 2. How may I show (statistically that is - and therefore what statistical
> analyses I should deploy) that w.r.t. t1 and t2 that condition_2 IS
> different from condition_1.
> 
> Thank you for advice/help.
> 
> bw 
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