[R] sciplot question

[Jarle Bjørgeengen]

On May 24, 2009, at 4:42 , Frank E Harrell Jr wrote:

> Jarle Bjørgeengen wrote:
>> On May 24, 2009, at 3:34 , Frank E Harrell Jr wrote:
>>> Jarle Bjørgeengen wrote:
>>>> Great,
>>>> thanks Manuel.
>>>> Just for curiosity, any particular reason you chose standard  
>>>> error , and not confidence interval as the default (the naming of  
>>>> the plotting functions associates closer to the confidence  
>>>> interval .... ) error indication .
>>>> - Jarle Bjørgeengen
>>>> On May 24, 2009, at 3:02 , Manuel Morales wrote:
>>>>> You define your own function for the confidence intervals. The  
>>>>> function
>>>>> needs to return the two values representing the upper and lower CI
>>>>> values. So:
>>>>>
>>>>> qt.fun <- function(x) qt(p=.975,df=length(x)-1)*sd(x)/ 
>>>>> sqrt(length(x))
>>>>> my.ci <- function(x) c(mean(x)-qt.fun(x), mean(x)+qt.fun(x))
>>>
>>> Minor improvement: mean(x) + qt.fun(x)*c(-1,1) but in general  
>>> confidence limits should be asymmetric (a la bootstrap).
>> Thanks,
>> if the date is normally distributed , symmetric confidence interval  
>> should be ok , right ?
>
> Yes; I do see a normal distribution about once every 10 years.

Is it not true that the students-T (qt(... and so on) confidence  
intervals is quite robust against non-normality too ?

A teacher told me that, the students-T symmetric confidence intervals  
will give a adequate picture of the variability of the data in this  
particular case.

Best rgds
Jarle Bjørgeengen