Re: st: plotting median and its confidence interval

[Alfonso Sánchez-Peñalver <alfonso.statalist@gmail.com>]

Hi Roger,

I just followed your suggestion, and when using -rcentile- in the way you described on the auto data, I get the following message:

unrecognized command:  sccendif

I am using Stata 13.1 January 15 2014 revision for Mac.

Best,

Alfonso

On Jan 21, 2014, at 8:10 AM, Roger B. Newson <r.newson@imperial.ac.uk> wrote:

> A possible alternative might be to use -rcentile- followed by -xsvmat-, instead of -bpmedian- followed by -parmest-. The -rcentile- and -xsvmat- packages can be downloaded from SSC. -rcentile- has the advantage that the confidence intervals are asymmetric, unlike the ones from -bpmedian- and -parmest-, which are symmetric. I would expect the asymmetric confidence intervals from -rcentile- to have a coverage probability closer to the advertized level than the symmetric confidence intervals produced by -bpmedian-. And the -rcentile- package can have -cluster()- options and weights, which are not implemented for -bpmedian-.
> 
> An example in the -auto- data might be:
> 
> rcentile weight, tdist
> xsvmat, from(r(cimat)) name(col) norestore
> 
> which will create a dataset with 1 observation and variables Percent, Centile, Minimum and Maximum, containing a percent (defaulting to 50), a median, and its lower and upper confidence limits. You can append several datasets like this and then use -eclplot- (also downloadable from SSC) to plot the confidence intervals against any variable you like.
> 
> I hope this helps.
> 
> Best wishes
> 
> Roger
> 
> Roger B Newson BSc MSc DPhil
> Lecturer in Medical Statistics
> Respiratory Epidemiology, Occupational Medicine
> and Public Health Group
> National Heart and Lung Institute
> Imperial College London
> Royal Brompton Campus
> Room 33, Emmanuel Kaye Building
> 1B Manresa Road
> London SW3 6LR
> UNITED KINGDOM
> Tel: +44 (0)20 7352 8121 ext 3381
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> Email: r.newson@imperial.ac.uk
> Web page: http://www.imperial.ac.uk/nhli/r.newson/
> Departmental Web page:
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> 
> Opinions expressed are those of the author, not of the institution.
> 
> On 21/01/2014 12:33, XU XIAO wrote:
>> Hi,
>> 
>> I am treating the data which have 3 time points, say 1965, 1985, 1995. Also, I have a bunch of vars on each time point.
>> 
>> 
>> var1 | var2 | var3———var8 | characteristic_vars | year
>> 1
>> 2
>> 3
>> 4
>> .
>> .
>> .
>> 
>> Now, since there is some skewness in the data, I want to plot the medians and their confidence intervals for different groups(based on the characteristic) in each year, and connect the median with a line. Basically, I want to see how the medians of these vars of different groups changed as time went by (going through the 3 time points).
>> 
>> What I have tried was:
>> 1. use .bpmedian to find median and ci for one var of one group
>> 2. use .parmest to save it into a dataset
>> 3. do it for each year
>> 4. append the 3 datasets i got from the previous steps
>> 5. use serrbar to plot it
>> After 5 steps, I got the plot for 1 var of 1 group, but I have 30 groups.
>> 
>> Is there any easier way to do it? I mean, is there something like ciplot but plotting median and ci of the median instead? Also, how can I show several vars in one plot like what we can do in ciplot?
>> 
>> I am looking forward to your reply,
>> Respectfully yours,
>> 
>> Xu
>> 
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