Not sure whether I understand this [Two-Stage / GS Designs]

posted by ElMaestro  – Denmark, 2012-10-22 18:34 (4626 d 03:59 ago) – Posting: # 9444
Views: 7,032

Dear Helmut,

:confused: – again.


I am sorry for this gibberish.

Lemme try and explain with a simple made-up case to illustrate my point:
After dosing 4x500 mg of Schützomycin to two random subjects (let's call them Helmut and Detlew for simplicity), I measure how high they can jump. We are interested in knowing the average jump height of these two... erm.. shall we call them 'cases'.
For Helmut I measure (in cm):39,41,51,43,53
For Detlew I measure (in cm):50,39,56,40,42
...and I will now assume IID and blahdeeblahdeeblah and therefore I use a linear model even though jump height presumably cannot be lower than zero and blahblahblah. Let's just do this in R:
Height=c(c(39,41,51,43,53), c(50,39,56,40,42))
Case=as.factor( c(   rep("Helmut",5), rep("Detlew",5)))
Model=lm(Height~0+Case)
 
summary(Model)

Call:
lm(formula = Height ~ 0 + Case)

Residuals:
   Min     1Q Median     3Q    Max
 -6.40  -5.15  -2.90   5.35  10.60

Coefficients:
           Estimate Std. Error t value Pr(>|t|)
CaseDetlew   45.400      3.043   14.92 4.02e-07 ***
CaseHelmut   45.400      3.043   14.92 4.02e-07 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 6.804 on 8 degrees of freedom
Multiple R-squared: 0.9823,     Adjusted R-squared: 0.9779
F-statistic: 222.6 on 2 and 8 DF,  p-value: 9.712e-08


(let me add: I will of course not fit with an intercept because then the model coefficients are not the LSMeans notch notch wink wink ;-)).

OK, so the two cases seem to perform equally terribly miserably bad under these assumptions for the normal linear model. Lord have mercy. In addition, I see that the residual st error is 6.804 under these circumstances. Aha...
But now I will introduce a game-changer: Let's say I know that the actual Mean for Helmut is 45 and that the actual Mean for Detlew is 47. These are not estimates but true values. Given that I know this, and given our observations, what would then be the most likely residual st error?

Pass or fail!
ElMaestro

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