R help - Oct 2012 - boot: how is t0 calculated?

Dear all,

I am doing log-transformed bootstrap regression using:

x=c(0.038,0.054,1.030,1.250,10.240,52.000,228.100,240.000,758.000,1502.600,0.140,9.170,280.000,1.000,0.150,0.388,20)
y=c(3961.5,25987.5,526557,321094.5,6433332,23592715.5,40500000,
228853521.1,320980392,429000000,58435.5,13525240.5,621195600,1020000,30567.0,296100.0,4800000)

xy = data.frame(x=x,y=y)

reg.ln = function(storage, indices){
   storage = storage[indices,]
   res.lm  = lm(log(y)~log(x), data=storage)
   coefficients(res.lm)
}

xy.boot = boot(xy, reg.ln, 2000)



Why does the Intercept given by xy.boot$t0 differs from 
mean(co.boot$t[,1])?
How are the t0 values calculated?

Any help is appreciated!

Thanks
Thomas

On Oct 22, 2012, at 3:28 PM, Thomas Hoffmann wrote:
> Dear all,
> 
> I am doing log-transformed bootstrap regression using:
> 
>
x=c(0.038,0.054,1.030,1.250,10.240,52.000,228.100,240.000,758.000,1502.600,0.140,9.170,280.000,1.000,0.150,0.388,20)
> y=c(3961.5,25987.5,526557,321094.5,6433332,23592715.5,40500000,
>
228853521.1,320980392,429000000,58435.5,13525240.5,621195600,1020000,30567.0,296100.0,4800000)
> 
> xy = data.frame(x=x,y=y)
> 
> reg.ln = function(storage, indices){
>  storage = storage[indices,]
>  res.lm  = lm(log(y)~log(x), data=storage)
>  coefficients(res.lm)
> }
> 
> xy.boot = boot(xy, reg.ln, 2000)
> 
> 
> 
> Why does the Intercept given by xy.boot$t0 differs from
mean(co.boot$t[,1])?
Hard to tell from this perspective:
> mean(co.boot$t[,1])
Error in mean(co.boot$t[, 1]) : 
  error in evaluating the argument 'x' in selecting a method for
function 'mean': Error: object 'co.boot' not found

Are you asking why 12.95 is not equal to 12.94?
> mean(xy.boot$t[,1])
[1] 12.95764
> lm(log(y)~log(x), data=xy) 
Call:
lm(formula = log(y) ~ log(x), data = xy)

Coefficients:
(Intercept)       log(x)  
     12.942        1.055  

> How are the t0 values calculated?
t0?
> Any help is appreciated!
That is what some of us are thinking, too.

-- 

David Winsemius, MD
Alameda, CA, USA