Statisticians_group : Message: Re: [Statisticians_group] Calculation of Confidence Interval

Edoardo,

I assume you want a confidence interval for the mean of the population which is generating Dataset C? One approach would be to calculate the approximate expectation & variance of each C_i=A_i/B_i, & use those to get a conf interval CI assuming approximate normality of C_i. E(C_i) & Var(C_i) are based on a first order Taylor expansion. If you need me to write them up for you I can probably do that next week, but I don't have them available at the moment.

On the philosophical side: Be aware that a CI does not indicate what most people think it indicates. The "95%" in "95% CI" means that, if you repeated the experiment many times, about 95% of the CIs would contain the parameter. We are not generally entitled to say that the probability is 95% that any given CI contains the parameter. Thus, the inferential meaning of a CI is unclear.

--- On Wed, 5/6/09, biotechbs <gedoardo83@...> wrote:

From: biotechbs <gedoardo83@...>
Subject: [Statisticians_group] Calculation of Confidence Interval
To: Statisticians_group@...
Date: Wednesday, May 6, 2009, 11:43 AM

Hi everybody,

This is my question. I have two set of data: set A (from A1 to A8) and set B (also from B1 to B8). Each value of both sets are calculated as average of a distinct group of measures and has its associated standard deviation.

Then I have another set of value (set C, the one I want to plot as final results) which is calculated as the ratio between each A value and correspondent B value (for example A1/B1, A2/B2, ecc.).

How can I calculate a confidence interval for set C values to use to plot error bars?

Thanks a lot.
Edoardo

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