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Re: st: error bars


From   "moleps islon" <moleps2@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: error bars
Date   Wed, 18 Jun 2008 22:30:08 +0200

I found cibplot which does what I need in terms of bars with
projecting error bars (cibplot x y, by(z)), however the graphs come
out the same way as ciplot. In other words identical, despite tabing
the different variables give completely different results.

On Wed, Jun 18, 2008 at 10:21 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
> Have a look at:
> R. Newson (2003), "Confidence intervals and p-values for delivery to
> the end user", The Stata Journal, 3(3), pp. 245--269.
> http://www.stata-journal.com/article.html?article=st0043
>
> I actually refered to that earlier (see below)
>
> -- Maarten
>
>
> --- moleps islon <moleps2@gmail.com> wrote:
>
>> I' making a double error bar graph- e.g two different variables x and
>> y with error bars categorised according to z. I've tried using ciplot
>> x y, by(z) however I get a graph with two identical error bars
>> (though
>> different symbol, but identical values) for each instance of z. Any
>> idea how to remedy this? If I need to make bars (a bar graph)  for
>> each category and then have the positive part of the error bar
>> projecting from the top- how do I go about this?
>>
>> Regards
>>
>>
>> On Mon, Jun 16, 2008 at 2:23 PM, Nick Cox <n.j.cox@durham.ac.uk>
>> wrote:
>> > Standard errors can come from lots of places, including the -ci-
>> > command.
>> >
>> > Moleps seems to be implying that -ci- does the right calculation
>> for his
>> > or her purposes.
>> >
>> > (I note that Moleps has yearly results, but -ci- for separate years
>> does
>> > nothing about any time series structure in the data, for example
>> about
>> > taking serial correlation into account.)
>> >
>> > -ciplot- and -stripplot- from SSC both do -ci-type calculations and
>> > graphing in one.
>> >
>> > Nick
>> > n.j.cox@durham.ac.uk
>> >
>> > Maarten buis
>> >
>> > --- moleps islon <moleps2@gmail.com> wrote:
>> >> I need to make a an error-bar graph categorised by year. I've
>> tried
>> >> using serrbar mean(x) etc, but I cant find a command for the
>> standard
>> >> error. Do I need to run a CI, generate a new variable from the ci
>> >> result and feed that into serrbar?
>> >
>> > There are many ways of doing this. For instance you can use methods
>> > discussed in (Buis 2007) (a convenient estimatation command would
>> in
>> > this case be -mean-), or you can remember that the standard error
>> of
>> > the mean is the standard deviation divided by the square root of
>> the
>> > number of observations, like in the example below:
>> >
>> > *-------------- begin example -----------------------
>> > sysuse nlsw88, clear
>> > gen mis = missing(wage, age)
>> > bys age: egen mwage = mean(wage)
>> > bys age: egen sdwage = sd(wage)
>> > bys age mis: gen se = sdwage/sqrt(_N) if mis == 0
>> > serrbar mwage se age, scale(1.96)
>> > *-------------- end example -------------------------
>> >
>> > Notice that a fixed scale is slightly problematic here as idealy
>> this
>> > scale should depend on the number of observations (a t-test), but
>> 1.96
>> > should work fine in large samples. For a more flexible approach,
>> where
>> > you can take all this into account see: (Newson 2003)
>> >
>> > -- maarten
>> >
>> > M.L. Buis (2007), "Stata tip 54: Where did my p-values go?", The
>> Stata
>> > Journal, 7(4), pp.584--586.
>> > http://home.fsw.vu.nl/m.buis/wp/pvalue.html
>> >
>> > R. Newson (2003), "Confidence intervals and p-values for delivery
>> to
>> > the end user", The Stata Journal, 3(3), pp. 245--269.
>> > http://www.stata-journal.com/article.html?article=st0043
>> >
>> >
>> > *
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>> >
>> *
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>>
>
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
>
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