<?xml version="1.0" encoding="utf-8"?><!DOCTYPE article  PUBLIC '-//OASIS//DTD DocBook XML V4.4//EN'  'http://www.docbook.org/xml/4.4/docbookx.dtd'><article><articleinfo><title>FAQ/distFAQ</title><revhistory><revision><revnumber>75</revnumber><date>2020-03-03 12:05:14</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>74</revnumber><date>2020-03-03 11:59:47</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>73</revnumber><date>2018-01-25 12:55:13</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>72</revnumber><date>2017-11-13 11:04:59</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>71</revnumber><date>2017-01-09 11:54:08</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>70</revnumber><date>2016-01-07 15:45:03</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>69</revnumber><date>2016-01-07 15:43:16</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>68</revnumber><date>2016-01-07 15:42:12</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>67</revnumber><date>2016-01-07 15:30:33</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>66</revnumber><date>2016-01-07 15:30:22</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>65</revnumber><date>2015-08-25 12:27:41</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>64</revnumber><date>2015-08-25 11:55:40</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>63</revnumber><date>2015-08-24 15:41:20</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>62</revnumber><date>2015-08-24 15:40:29</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>61</revnumber><date>2015-08-24 15:32:47</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>60</revnumber><date>2015-08-24 15:32:36</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>59</revnumber><date>2015-06-30 10:23:10</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>58</revnumber><date>2014-10-28 14:55:14</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>57</revnumber><date>2014-03-07 12:24:51</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>56</revnumber><date>2014-03-03 11:26:17</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>55</revnumber><date>2014-03-03 11:09:36</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>54</revnumber><date>2013-12-10 10:23:49</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>53</revnumber><date>2013-12-02 16:49:51</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>52</revnumber><date>2013-10-03 13:56:00</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>51</revnumber><date>2013-04-10 09:49:21</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>50</revnumber><date>2013-03-08 10:17:30</date><authorinitials>localhost</authorinitials><revremark>converted to 1.6 markup</revremark></revision><revision><revnumber>49</revnumber><date>2012-07-10 15:08:51</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>48</revnumber><date>2012-07-10 09:24:28</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>47</revnumber><date>2012-07-05 09:09:50</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>46</revnumber><date>2012-07-05 09:09:24</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>45</revnumber><date>2012-02-29 09:40:23</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>44</revnumber><date>2012-02-17 11:39:50</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>43</revnumber><date>2012-01-18 16:55:54</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>42</revnumber><date>2011-11-02 16:32:57</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>41</revnumber><date>2011-11-02 16:02:24</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>40</revnumber><date>2011-02-01 15:53:12</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>39</revnumber><date>2010-08-19 14:02:28</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>38</revnumber><date>2010-04-15 14:33:02</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>37</revnumber><date>2010-04-15 13:48:50</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>36</revnumber><date>2010-01-25 13:02:31</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>35</revnumber><date>2009-12-03 15:00:41</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>34</revnumber><date>2009-12-03 14:50:07</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>33</revnumber><date>2009-11-30 10:51:36</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>32</revnumber><date>2009-07-23 15:19:02</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>31</revnumber><date>2009-02-24 13:35:23</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>30</revnumber><date>2009-02-18 10:55:40</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>29</revnumber><date>2009-01-12 16:32:51</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>28</revnumber><date>2008-12-08 16:20:22</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>27</revnumber><date>2008-12-08 14:34:57</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>26</revnumber><date>2008-11-11 16:42:14</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>25</revnumber><date>2008-11-11 16:42:00</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>24</revnumber><date>2008-10-14 14:32:02</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>23</revnumber><date>2008-09-03 10:03:21</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>22</revnumber><date>2008-08-15 11:15:46</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>21</revnumber><date>2008-08-15 10:51:19</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>20</revnumber><date>2008-05-13 12:06:43</date><authorinitials>IanNimmoSmith</authorinitials></revision><revision><revnumber>19</revnumber><date>2008-05-13 12:04:50</date><authorinitials>IanNimmoSmith</authorinitials></revision><revision><revnumber>18</revnumber><date>2008-05-02 10:28:45</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>17</revnumber><date>2008-05-02 10:06:02</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>16</revnumber><date>2008-04-30 15:33:45</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>15</revnumber><date>2008-04-11 10:48:20</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>14</revnumber><date>2008-04-08 10:55:57</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>13</revnumber><date>2008-04-07 15:56:48</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>12</revnumber><date>2008-03-04 18:56:17</date><authorinitials>IanNimmoSmith</authorinitials></revision><revision><revnumber>11</revnumber><date>2008-02-12 16:41:09</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>10</revnumber><date>2008-02-12 16:36:32</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>9</revnumber><date>2008-02-11 14:50:39</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>8</revnumber><date>2008-02-11 14:26:58</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>7</revnumber><date>2007-11-07 15:45:21</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>6</revnumber><date>2007-10-03 10:02:59</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>5</revnumber><date>2007-08-15 14:25:17</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>4</revnumber><date>2007-04-26 16:28:17</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>3</revnumber><date>2007-04-26 16:26:43</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>2</revnumber><date>2006-09-29 13:13:17</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>1</revnumber><date>2006-09-29 13:13:05</date><authorinitials>PeterWatson</authorinitials></revision></revhistory></articleinfo><section><title>Questions about distributions of random variables</title><orderedlist numeration="arabic"><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/normN#">How many observations do I need to make z-scoring (assuming Normality) feasible?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/stables#">Are there any on-line statistical tables for commonly used distributions?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/Sattherthwaite#">Why are the degrees of freedom not whole numbers?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/ztcF#">What is the relationship between the z, t, chi-square and F distributions?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/distFAQ?action=AttachFile&amp;do=get&amp;target=asymmetry.pdf">A Normalising transformation of ratios of form (L-R)/(L+R)</ulink>  </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/Combinatorics#">What is the probability of a repetition in a sequence of size k taken from K stimuli?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/multi#">How do I evaluate Multinomial probabilities of pooled trial frequencies of locations of peaks which can occur in one of K positions in each trial?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/wblfit#">How do I fit a Weibull distribution to scores over time using MATLAB and notes on using non-linear least squares?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/recode#">How do I recode levels of a group variable in SPSS?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/itt#">What is an intention to treat analysis?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/aster#">How do I evaluate a number to a general power in SPSS?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/cis#">A note on comparing confidence intervals and statistical significance</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/poolse#">How do I obtain a pooled standard error of the mean?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/semsd#">How do I obtain the standard deviation from the standard error of the mean (s.e.m.) and how does this and the mean vary with sample size?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/FVars#">What is the variance of the mean of my transformed data and the variance of combinations of means?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/wttest#">How do I do a t-test between two weighted means?</ulink>  </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/meanmed#">What is the relationship between the mean and the median from a sample and how do I compute 95% CIs for the median?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/thirds#">What is an optimal cut-off for the discretization/splitting of a continuous variable and how do we use this in a regression?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/eorder#">A quick approximation for Normally distributed expected order statistics</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/zpercs#">How do I convert a z-score into a percentile in SPSS?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/subscale#">How do I derive an expected total for a subset of items based on the expected overall total?</ulink>  </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/absdiff#">How do I compute a difference in errors adjusted for overall number of errors when the errors have different signs?</ulink>  </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/ResidualsNonNormality#">Residuals and (Non-)Normality</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/ResidsRepMeas#">How do I check Normality assumptions in repeated measures analyses in SPSS?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/Simon#">Testing normality including rules of thumb for skew, kurtosis in SPSS</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/Winsor#">Methods of handling outliers.</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/EXponential#">How do I produce truncated exponential random variables using MATLAB?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/mixtures#">How do I obtain parameter estimates for finite Normal mixture distributions using SPSS and BMDP?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/perc#">How do I find out how many people have a score above a certain value?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/percentile#">How do I compute percentile thresholds for exponential data and use in outlier detection?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/rand#">How do I generate a random sample in EXCEL?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/randall#">Matching groups and randomized allocation to groups</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/rtest#">Some thoughts on testing for randomness</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/MeanSum#">How do I obtain the mean of several variables, each minus the same constant? (In SPSS)</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/zscore#">How do I compute z-scores in SPSS and what is their relationship to comparing group means?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/signt#">Why does my t-statistic have a negative sign?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/pvals#">How do I use cumulative distribution functions to compute p-values in SPSS, EXCEL and R?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/surv#">How do I adjust for age in comparing survival times in two different groups?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/t1t2#">What is the relationship between intercept and slope for scores at two time points?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/atan#">Arctan functions in EXCEL.</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/cdfs#">How do I obtain statistical distributions in MATLAB?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/gamma#">How do I produce random variables which follow a negative skew distribution?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/multinorm#">How do I calculate probabilities involving the multivariate normal distribution?</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/boot#">Simulations sampling from data with replacement (bootstrapping)</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/secretS#">Bootstrapping without replacement (Secret Santa) in R</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/mvngen#">Generating multivariate data with a required correlation matrix</ulink> </para></listitem><listitem><para><ulink url="https://imaging.mrc-cbu.cam.ac.uk/statswiki/FAQ/distFAQ/statswiki/FAQ/formulae#">How do I obtain the formulae behind statistics outputted by SPSS algorithms?</ulink> </para></listitem></orderedlist></section></article>