Re: getting the confidence interval

[Alan Mead]

I think John is saying that in SPSS/PSPP you need to use a statistical function to generate statistical results like a CI. For example, T-TEST will produce a 95% CI for the mean difference in independent-samples t-tests. Other routines may provide other confidence intervals.

But maybe you want to use compute to create a variable for each case:

compute LB = x - 1.96 * 10.1/sqrt(31).
compute UB = x + 1.96 * 10.1/sqrt(31).

This creates variables LB and UB for all cases in your data file and you need to supply Z, mean, SD, and n.

Connecting that to your query about AGGREGATE, which takes groups of cases (defined by unique values on BREAK) and creates summary stats, you could use AGGREGATE to create mean, SD and n in the above equation and then use those compute statements to calculate the bounds of the CI for the groups of cases. So, you would have to do two steps. First an AGGREGATE command that creates mean, SD and n, followed by the two computes above.

You would end up with a dataset containing the mean, sd, n, LB, and UB for each group (defined by a unique value of BREAK) in the original dataset.

Hopefully you only have one variable (or a very few) in the data that you want this on, because you have to create mean, SD and n for each variable.

-Alan

On 10/12/2018 8:01 AM, Mark Hancock wrote:

I unfortunately don't know enough about PSPP syntax to suggest how to do this, but a CI is not always associated with a hypothesis and can be calculated from just a mean and SD (and a cumulative distribution function, which is typically the normal one). Typically the formula is something like:

mean ± z(SD/sqrt(n)), where z is from the CDF.

On Fri, Oct 12, 2018 at 6:29 AM John Darrington <address@hidden> wrote:

The confidence interval is a concept associated with a hypothesis.
If it's the confidence interval on the test for a mean value, typically you
would get that by using a T-Test.


On Fri, Oct 12, 2018 at 10:40:22AM +0200, Werner LEMBERG wrote:

     Folks,


     I would like to get a 95% confidence interval so that I could use it
     in AGGREGATE, e.g.,

       AGGREGATE OUTFILE * MODE ADDVARIABLES
         /BREAK=...
         /Mean = mean(V)
         /CI = ci(V, 0.95)

     What must I do to get the result of my hypothetical `ci' function?
     I'm a PSPP novice, so maybe there is a better solution than AGGREGATE
     ??? what I ultimately want is to emit the confidence interval of a
     variable to a CSV file using SAVE TRANSLATE.


         Werner
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