[R] help with predict and plotting confidence intervals

[David Winsemius]

On Mar 12, 2009, at 11:45 AM, David Winsemius wrote:

>
> On Mar 12, 2009, at 11:14 AM, Michael Denslow wrote:
>
>>
>>
>> # I am not sure how to get the lines to draw correctly here
>> matlines(pred.frame$a,pp, lty=c(1,2,2),col="black")
>>
> The x values are your sequence whereas the y values are in the  
> sequence from the original data. They are not correctly associated  
> with each other.
>
> Try:
> pp <- predict(lm(wt.data$logS~wt.data$logA), int = "p", newdata=  
> data.frame(logA=seq(0,6, length.out = 24))  )
> plot(pp)
>
At this point I should not have accepted your starting point. A better  
starting point would be to use the wt.mod model:

pp <- predict(wt.mod, int = "p", newdata= list(logA=seq(0,6,  
length.out = 24)) )

# Followed by:

plot( seq(0,6, length.out = 24),  pp[ ,"fit"] )
  lines(seq(0,6, length.out = 24),  pp[ ,"lwr"], lty=2)
  lines(seq(0,6, length.out = 24),  pp[ ,"upr"], lty=2)


> -- 
> david winsemius
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT