The Wikipedia article (Student_t_distribution) is pretty good.One very important thing to note when doing a Student t-test is that you must know the degrees of freedom first! That is a separate calculation that is typically found as an integral over the product of the autocorrelation functions of the two variables. There are several other essential subtleties, that are described in, among other places, p3015 of Kessler et al (1996, JPO, link to the pdf at the end of this message).
Statistics are hard. Billy KLink to the paper with description of the procedure and assumptions (pdf, see p3015):
http://faculty.washington.edu/kessler/abstracts/ksmh-1996.pdf
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On 21 May 2010, at 9:12 AM, Steve Hankin wrote:
Hi Sarah,If you have a variable that contains the statistical confidence values, then the result is easy:LET var95 = IF confidence GE 0.95 THEN my_varThe values in var95 will be masked to include only those where you have 95% confidence. Others will be set to "missing" and become invisible.I am not aware of a student t-test function in Ferret, but it is the sort of calculation that can be readily put into an external function (and thereafter made sharable for other Ferret users).- Steve ======================================= Sarah Bonham wrote:Dear Ferret users,I have 2 sets of temperature data, both on a 73x96 array and I am trying to produce a map of the difference between the two showing only temperature values that have a 95% confidence.Is there a function in ferret to apply a student t-test or something similar?Ideally, I would just like to map the temperatures that have 95% confidence, but if this isn't possible and there is a way to put shading over the top instead, then this would be great to.Any help is greatly appreciated, thank you in advance, Sarah
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ William S. Kessler NOAA / Pacific Marine Environmental Laboratory 7600 Sand Point Way NE Seattle WA 98115 USA william.s.kessler@xxxxxxxx Tel: 206-526-6221 Fax: 206-526-6744 Web: http://www.pmel.noaa.gov/people/kessler