First of all I have to apologize because my english is horrible. 

I am working in a basic and practical statistic course. 

I will speak about confidence intervals, of course. 

But when I was preparing this chapter I had a doubt: I wonder if it has sence 
today to explain the confidence intervals for a mean in terms of the standard 
normal distribution. 

If we show that the mean follows a normal distribution with variance/n then it 
is easy to explain (and to understand) that the confidence interval is due to 
two percentiles, the percentile alpha/2 and the percentile 1-alpha/2 from a 
normal distribution with the sample mean and the sample variance/n. 

I think that the standard gaussian distribution was usefull when we had to 
calculate CI in the past. 
That is, it was a simple way to have all possibilities in a single table (in 
paper). 

But now, we have R functions that let us to obtain the exact values for any 
normal distribution. 

I think that is not necessary to explain how to work with transformations if we 
can explain that a CI is simply to identify percentiles. 

What do you think?

Thanks

PD I know that the normal distribution for CI need some hipothesis. But I have 
focused the question

_________________________

David Monterde

Lo difĂ­cil se hace. 
Lo imposible se intenta. 
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