Re the description Ansley points
to below:
You can make a t-table in fortran (requires a
Gamma-function routine, see Numerical Recipes), or use
the attached lookup table. Or you can probably find it
via google.
But the key thing you need to do this correctly is an
estimate of the degrees of freedom. Very roughly this
is the number of "bumps" in your time series
(including positive and negative), but is formally:
(Number of terms in the time series)/(Independence
timescale)
The independence timescale is usually found as the sum
(over all lags) of the product of lag correlations (or
lag correlation squared for a single time series).
This is tricky to do in Ferret (usually requires a
REPEAT loop), but the extra axes available in Ferret
6.8 are helpful.
Be careful about the time units! If you are using
"time axis index number" as your unit, and the time
axis is regular, the calculation is as above. If you
do it in, say, days, then the independence timescale
is Delta-t (in days) times the sum of correlations,
and the "number of terms" above is the total length of
the time series in days.
See the discussion and references on p3015 of Kessler
et al (1996). Scales of variability in the equatorial
Pacific inferred from the Tropical Atmosphere- Ocean
(TAO) buoy array. J.Climate, 9, 2999-3024.
Available in pdf at
http://faculty.washington.edu/kessler/abstracts/sampling-abstract.html
BK
On Nov 5, 2012, at 11:49 , Ansley Manke wrote:
> Hi,
> Here is a message from the list, which talks a
bit about using a correlation to determine
significance of a trend line using a Student's t-test.
>
>
http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2009/msg00482.html
>
> if this is not similar to what you want to do,
then please search the Ferret archives some more for
other possible answers , or write back with more
information about the data you are working with and
what you want to do with it.
>
> Ansley
>
>
> On 11/1/2012 1:12 PM, FISSEHA G. BERHANE wrote:
>>
>> Hello dear Ferreters,
>>
>> I have composite analyses and I want to do
significance test of my results. Can I do it in
Ferret?
>>
>> Thank you,
>> Fisseha
>