<div dir="ltr">Hi Adam,<div><br></div><div>thanks for your suggestion; indeed I suspected there could be issues with the choice of xN and yN. In fact I have played with these numbers, but unfortunately even setting them to 10 does not change much (see attached plot). In any case I agree that 10 ensemble members is not a high number for ensemble statistics. Do you think the strange probability pattern in the plot could be due to this fact?</div><div><br></div><div>thanks,</div><div>Anne</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jan 18, 2019 at 8:12 PM Adam Phillips <<a href="mailto:asphilli@ucar.edu">asphilli@ucar.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">Hi Anne,<div>You are calling equiv_sample_size (which we usually recommend), and then your are calling wgt_areaave to arrive at one number:</div><div><div><span style="white-space:pre-wrap"> </span> xEqv = equiv_sample_size (jfm_s, sigr, 0)</div><div><span style="white-space:pre-wrap"> </span> yEqv = equiv_sample_size (jfm_c, sigr, 0)</div></div><div><div><span style="white-space:pre-wrap"> </span> xN = wgt_areaave (xEqv, 1., 1., 0) ; wgty could be gaussian weights </div><div><span style="white-space:pre-wrap"> </span> yN = wgt_areaave (yEqv, 1., 1., 0) </div><div> prob = 100.*(ttest(ave_s, VAR_s, xN, ave_c, VAR_c, yN, iflag, tval_opt))<br></div></div><div><br></div><div>To simplify things you could replace xN and yN with 10 (=the number of ensemble members, or sample size). But note: Depending on the field you are looking at 10 samples is not a large number, especially if there is high autocorrelation. This also might result in values coming out of equiv_sample_size = 1 or 0, which might cause issues in the ttest function.</div><div><br></div><div>Hope that helps. If you have further questions let ncl-talk know.</div><div>Adam</div></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail-m_1680155318860865442gmail_attr">On Thu, Jan 17, 2019 at 2:14 PM Anne <<a href="mailto:anne.seidenglanz@unive.it" target="_blank">anne.seidenglanz@unive.it</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr">Hi everyone,<div><br></div><div>I have some issues using the built-in 'ttest' function. When I plot the 'raw' probability (so regardless of any significance level), I end up with a rather strange plot, see attached. </div><div>I followed example 4 from the documentation at <a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/ttest.shtml" target="_blank">https://www.ncl.ucar.edu/Document/Functions/Built-in/ttest.shtml</a>, just that instead of time I have ensemble member as the right-most dimension, and hence compute mean and variance of the ensemble members. So my two fields each have the following dimensions:</div><div>Dimensions and sizes:<span style="white-space:pre-wrap"> </span>[Ens | 10] x [lat | 180] x [lon | 360]<br></div><div><br></div><div>Fields for mean and variance look fine, but there is something wrong with the probability plot. I attach also the script. </div><div><br></div><div>Thanks for any advice,</div><div>Anne </div><div></div></div></div></div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail-m_1680155318860865442gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div><div><span><font color="#888888">Adam Phillips <br></font></span></div><span><font color="#888888">Associate Scientist, </font></span><span><font color="#888888">Climate and Global Dynamics Laboratory, NCAR<br></font></span></div></div><div><span><font color="#888888"><a href="http://www.cgd.ucar.edu/staff/asphilli/" target="_blank">www.cgd.ucar.edu/staff/asphilli/</a> </font></span><span><font color="#888888">303-497-1726 </font></span></div><span><font color="#888888"></font></span><div><div><span><font color="#888888"><br></font></span><div><span><font color="#888888"><a href="http://www.cgd.ucar.edu/staff/asphilli" target="_blank"></a></font></span></div></div></div></div></div></div></div></div></div></div></div>
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