[Met_help] [rt.rap.ucar.edu #71419] History for CI for MET-TC tc_stat

[John Halley Gotway via RT]

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  Initial Request
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Hi there,

In the output from MET-TC (tc_stat), I'm wondering how the MEAN_NCL and
MEAN_NCU columns are computed. I'm assuming these are the lower and upper
confidence intervals, is this correct? If so, how is this computed? I've
attached a sample output file for reference.

​Thanks,
Andy​

-- 
Andrew Penny
Hurricane Model Diagnostician
SRG / National Hurricane Center
11691 SW 17th Street
Miami, FL 33165-2149
phone: 305.229.4457
email: andrew.penny at noaa.gov


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  Complete Ticket History
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Subject: CI for MET-TC tc_stat
From: John Halley Gotway
Time: Mon Apr 13 15:23:52 2015

Andy,

You are correct, NCL and NCL stand for normal confidence interval
lower and
upper limits.

In the same data you sent, the first line not containing missing data
is a
mean value of 10.81587 with a normal CI of (9.88275, 11.749) computed
over
315 values.  The standard deviation of the 315 values is 8.4498.

The CI is computed by the function named "compute_mean_stdev()"
defined in:
   src/libcode/vx_statistics/met_stats.cc

The CI equation is basically this:
  mean +/- z * stdev / sqrt(n)

Where "z" is the critical value as determined by the alpha value
(default
alpha of 0.05 means a 95% CI).  For a 2-tailed 95% CI, z = 1.96.
Using
your data values, that's:
   10.81587 +/- 1.96 * 8.4498 / 17.7482 = 10.81587 +/- 0.93314 =
(9.8827,
11.749)

Hope that helps.

Thanks,
John





On Mon, Apr 13, 2015 at 8:02 AM, Andrew Penny - NOAA Affiliate via RT
<
met_help at ucar.edu> wrote:

>
> Mon Apr 13 08:02:57 2015: Request 71419 was acted upon.
> Transaction: Ticket created by andrew.penny at noaa.gov
>        Queue: met_help
>      Subject: CI for MET-TC tc_stat
>        Owner: Nobody
>   Requestors: andrew.penny at noaa.gov
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=71419 >
>
>
> Hi there,
>
> In the output from MET-TC (tc_stat), I'm wondering how the MEAN_NCL
and
> MEAN_NCU columns are computed. I'm assuming these are the lower and
upper
> confidence intervals, is this correct? If so, how is this computed?
I've
> attached a sample output file for reference.
>
> ​Thanks,
> Andy
>
> --
> Andrew Penny
> Hurricane Model Diagnostician
> SRG / National Hurricane Center
> 11691 SW 17th Street
> Miami, FL 33165-2149
> phone: 305.229.4457
> email: andrew.penny at noaa.gov
>
>

------------------------------------------------
Subject: CI for MET-TC tc_stat
From: Andrew Penny - NOAA Affiliate
Time: Tue Apr 14 05:16:15 2015

Thanks for the explanation, John. Very much appreciated!

Take care,
Andy

On Mon, Apr 13, 2015 at 5:23 PM, John Halley Gotway via RT <
met_help at ucar.edu> wrote:

> Andy,
>
> You are correct, NCL and NCL stand for normal confidence interval
lower and
> upper limits.
>
> In the same data you sent, the first line not containing missing
data is a
> mean value of 10.81587 with a normal CI of (9.88275, 11.749)
computed over
> 315 values.  The standard deviation of the 315 values is 8.4498.
>
> The CI is computed by the function named "compute_mean_stdev()"
defined in:
>    src/libcode/vx_statistics/met_stats.cc
>
> The CI equation is basically this:
>   mean +/- z * stdev / sqrt(n)
>
> Where "z" is the critical value as determined by the alpha value
(default
> alpha of 0.05 means a 95% CI).  For a 2-tailed 95% CI, z = 1.96.
Using
> your data values, that's:
>    10.81587 +/- 1.96 * 8.4498 / 17.7482 = 10.81587 +/- 0.93314 =
(9.8827,
> 11.749)
>
> Hope that helps.
>
> Thanks,
> John
>
>
>
>
>
> On Mon, Apr 13, 2015 at 8:02 AM, Andrew Penny - NOAA Affiliate via
RT <
> met_help at ucar.edu> wrote:
>
> >
> > Mon Apr 13 08:02:57 2015: Request 71419 was acted upon.
> > Transaction: Ticket created by andrew.penny at noaa.gov
> >        Queue: met_help
> >      Subject: CI for MET-TC tc_stat
> >        Owner: Nobody
> >   Requestors: andrew.penny at noaa.gov
> >       Status: new
> >  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=71419 >
> >
> >
> > Hi there,
> >
> > In the output from MET-TC (tc_stat), I'm wondering how the
MEAN_NCL and
> > MEAN_NCU columns are computed. I'm assuming these are the lower
and upper
> > confidence intervals, is this correct? If so, how is this
computed? I've
> > attached a sample output file for reference.
> >
> > ​Thanks,
> > Andy
> >
> > --
> > Andrew Penny
> > Hurricane Model Diagnostician
> > SRG / National Hurricane Center
> > 11691 SW 17th Street
> > Miami, FL 33165-2149
> > phone: 305.229.4457
> > email: andrew.penny at noaa.gov
> >
> >
>
>


--
Andrew Penny
Hurricane Model Diagnostician
SRG / National Hurricane Center
11691 SW 17th Street
Miami, FL 33165-2149
phone: 305.229.4457
email: andrew.penny at noaa.gov

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