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--></style></head><body lang=EN-US link=blue vlink="#954F72"><div class=WordSection1><p class=MsoNormal>I basically have two gfs experiments and computed anomaly correlations to see if they are significantly different. I then computed differences in the two and want to use the t test to test this. But ncep uses the 2 sigma standard deviation with a varying z value based on sample size. I am not sure if these are the same or different, and if so, which one to use. Thanks Dennis </p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Andrew Kren</p><p class=MsoNormal><o:p> </o:p></p><div style='mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='border:none;padding:0in'><b>From: </b><a href="mailto:shea@ucar.edu">Dennis Shea</a><br><b>Sent: </b>Tuesday, April 4, 2017 2:26 PM<br><b>To: </b><a href="mailto:andrew.kren@noaa.gov">Andrew Kren - NOAA Affiliate</a><br><b>Cc: </b><a href="mailto:ncl-talk@ucar.edu">ncl-talk</a><br><b>Subject: </b>Re: [ncl-talk] computing confidence interval from ttest</p></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'>I would say so ... However, to be upfront, I am not sure of he original question. </p></div><p class=MsoNormal>Note that correlations are bounded [-1 to +1]. Hence, not 'normally distributed.' Usually, the correlations are put into a normal distribution via the Fischer z-transform. Means and std dev are in 'z-space'; the results are transformed back<br> </p></div><p class=MsoNormal style='margin-bottom:12.0pt'> Look at the example for <br> <a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/escorc.shtml">https://www.ncl.ucar.edu/Document/Functions/Built-in/escorc.shtml</a></p></div><p class=MsoNormal>It uses the large sample size z-value1.96 ... you can use the tvalue since tval ==> zval for large sample size</p><div><pre> zlow = z - 1.96*se ; 95% (2.58 for 99%)</pre><pre> zhi = z + 1.96*se </pre><pre> </pre><p class=MsoNormal style='margin-bottom:12.0pt'><br><br></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p></div></div></div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Tue, Apr 4, 2017 at 2:07 PM, Andrew Kren - NOAA Affiliate <<a href="mailto:andrew.kren@noaa.gov" target="_blank">andrew.kren@noaa.gov</a>> wrote:</p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><p class=MsoNormal style='margin-left:4.8pt'>Thanks Dennis,</p><div><p class=MsoNormal style='margin-left:4.8pt'>In general, can the ttest be run on anomaly correlations?</p></div></div><div><div><div><p class=MsoNormal style='margin-left:4.8pt'><o:p> </o:p></p><div><p class=MsoNormal style='margin-left:4.8pt'>On Tue, Apr 4, 2017 at 2:01 PM, Dennis Shea <<a href="mailto:shea@ucar.edu" target="_blank">shea@ucar.edu</a>> wrote:</p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><div><div><div><p class=MsoNormal style='margin-left:9.6pt'>Has anybody answered your question?<br><br><a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda352.htm" target="_blank">http://www.itl.nist.gov/div898/handbook/eda/section3/eda352.htm</a></p></div><p class=MsoNormal style='margin-left:9.6pt'>See the definition of the confidene interval.<br><br> tval_opt =True ; p & t-value<br> pt = ttest(aveX,varX,sX, aveY,varY,sY, iflag, tval_opt)</p></div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:9.6pt'> print(pt)</p></div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:9.6pt'>The 2nd element is the t-value</p></div><p class=MsoNormal style='margin-left:9.6pt'>HTH</p><div><p class=MsoNormal style='margin-left:9.6pt'><o:p> </o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:9.6pt'><o:p> </o:p></p><div><p class=MsoNormal style='margin-left:9.6pt'><o:p> </o:p></p></div></div></div></div></div><div><p class=MsoNormal style='margin-left:9.6pt'><o:p> </o:p></p><div><div><div><p class=MsoNormal style='margin-left:9.6pt'>On Fri, Mar 31, 2017 at 3:49 PM, Andrew Kren - NOAA Affiliate <<a href="mailto:andrew.kren@noaa.gov" target="_blank">andrew.kren@noaa.gov</a>> wrote:</p></div></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><div><p class=MsoNormal style='margin-left:.2in'>Dear ncl-talk,</p><div><p class=MsoNormal style='margin-left:.2in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.2in'>I'm using the function ttest in NCL to compute the two-tailed significance of a set of correlations. I plot the correlations (anomaly) as a time series as most people do. I compute the difference between the two and want to also plot an envelope that encompasses the 95% confidence range for the range of values. Is there a way to determine this from the ttest? <span style='color:#888888'><br clear=all><span class=m-5599711679072778743m2612023742121366583hoenzb><o:p></o:p></span></span></p><div><p class=MsoNormal style='margin-left:.2in'><o:p> </o:p></p></div><p class=MsoNormal style='margin-left:.2in'><span class=m-5599711679072778743m2612023742121366583hoenzb><span style='color:#888888'>-- </span><o:p></o:p></span></p><div><div><div><div><div><div><div><div><div><div><div><div><div><div><p class=MsoNormal style='margin-left:.2in'><span style='color:#888888'>Andrew Kren, PhD<br>Research Scientist I, Global Observing Systems Analysis (GOSA) Group<br>NOAA ESRL Global Systems Division (Rm 3C515)<br>325 Broadway, Boulder, CO 80305<br><a href="tel:%28303%29%20497-5418" target="_blank">(303) 497-5418</a></span></p></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div><p class=MsoNormal style='margin-left:.2in'><o:p> </o:p></p></div></div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:.2in'>_______________________________________________<br>ncl-talk mailing list<br><a href="mailto:ncl-talk@ucar.edu" target="_blank">ncl-talk@ucar.edu</a><br>List instructions, subscriber options, unsubscribe:<br><a href="http://mailman.ucar.edu/mailman/listinfo/ncl-talk" target="_blank">http://mailman.ucar.edu/mailman/listinfo/ncl-talk</a></p></blockquote></div><p class=MsoNormal style='margin-left:9.6pt'><o:p> </o:p></p></div></blockquote></div><p class=MsoNormal style='margin-left:4.8pt'><br><br clear=all></p><div><p class=MsoNormal style='margin-left:4.8pt'><o:p> </o:p></p></div><p class=MsoNormal style='margin-left:4.8pt'>-- </p><div><div><div><div><div><div><div><div><div><div><div><div><div><div><p class=MsoNormal style='margin-left:4.8pt'>Andrew Kren, PhD<br>Research Scientist I, Global Observing Systems Analysis (GOSA) Group<br>NOAA ESRL Global Systems Division (Rm 3C515)<br>325 Broadway, Boulder, CO 80305<br><a href="tel:%28303%29%20497-5418" target="_blank">(303) 497-5418</a></p></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></blockquote></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>