Quartiles and Inter-Quartile Range

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Quartiles and Inter-Quartile Range

 Why am I getting a wrong result for quartiles? here is my code: > cbiomass = c(910, 1058, 929, 1103, 1056, 1022, 1255, 1121, 1111, 1192, 1074, 1415) > summary(cbiomass) > IQR(cbiomass) The result R gives me is: For the summary > Min. 1st Qu.  Median    Mean 3rd Qu.    Max.     910    1048    1088    1104    1139    1415 For IQR > 91.25 ********* The true Q1 is 1039 and not 1048. Q2 is 1156.5 and not 1139. And the Inter-Quartile Range is 117.5 and not 91.25 How can I get these number right?
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Re: Quartiles and Inter-Quartile Range

 It's looks like you think that type=2 are the 'true' quantiles, but the default method in R is type=7 You might want to look at ?stats::quantile hth david freedman
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Re: Quartiles and Inter-Quartile Range

 Interestingly, Hmisc::describe() and summary() seem to be using one Type, and stats::fivenum() seems to be using another Type. > fivenum(cbiomass) [1]  910.0 1039.0 1088.5 1156.5 1415.0 > summary(cbiomass)    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.     910    1048    1088    1104    1139    1415 > describe(cbiomass)\$counts        n  missing   unique     Mean      .05      .10      .25      .50      .75     "12"      "0"     "12"   "1104" " 920.5" " 938.3" "1047.5" "1088.5" "1138.8"      .90      .95 "1248.7" "1327.0" cheers, -Girish
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Re: Quartiles and Inter-Quartile Range

 and SAS give one a choice of 5 option, and i'm fairly sure that it used a different default than does R (although one of the 5 corresponds to the sas default) see pctldef on http://www.technion.ac.il/docs/sas/proc/z0146803.htmmy simple brain thinks of thinks of the problem as 'how does one calculate the median of 4 values?' david freedman Girish A.R. [via R] wrote: > Interestingly, Hmisc::describe() and summary() seem to be using one > Type, and stats::fivenum() seems to be using another Type. > > > fivenum(cbiomass) > [1]  910.0 1039.0 1088.5 1156.5 1415.0 > > summary(cbiomass) >    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. >     910    1048    1088    1104    1139    1415 > > describe(cbiomass)\$counts >        n  missing   unique     Mean      .05      .10      .25     >  .50      .75 >     "12"      "0"     "12"   "1104" " 920.5" " 938.3" "1047.5" > "1088.5" "1138.8" >      .90      .95 > "1248.7" "1327.0" > > cheers, > -Girish > > View message @ > http://n4.nabble.com/Quartiles-and-Inter-Quartile-Range-tp1145817p1248728.html  > > To unsubscribe from Re: Quartiles and Inter-Quartile Range, click here > . > >
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RE: Quartiles and Inter-Quartile Range

 In reply to this post by David Freedman 2 Thank you David. I got it now.Maybe you can help again.I am typing the following code to draw a QQ plot but the line does not look right?*******************qqnorm(cbiomass)qqline(cbiomass)***********************the graph looks very different from the graph generated by SAS.Thank you again.Emiliano.Date: Fri, 22 Jan 2010 21:32:26 -0800From: [hidden email]To: [hidden email]Subject: Re: Quartiles and Inter-Quartile Range It's looks like you think that type=2 are the 'true' quantiles, but the default method in R is type=7 You might want to look at ?stats::quantile hth david freedman View message @ http://n4.nabble.com/Quartiles-and-Inter-Quartile-Range-tp1145817p1213199.html To unsubscribe from Quartiles and Inter-Quartile Range, click here. Quer fazer um álbum íncrivel? Conheça o Windows Live Fotos clicando aqui.
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Re: Quartiles and Inter-Quartile Range

 please do some reading - I *think* the main difference is that the x and y axes are reversed, but I really don't know what SAS prints outthere are a many 'defaults' that are rather arbitrary - sometimes SAS uses 1, while R uses another ??qqnorm brings up a list of functions, including stats::qqnorm?stats::qqnorm brings up the help page for the functionOn Mon, Jan 25, 2010 at 12:41 PM, eeramalho [via R] wrote: Thank you David. I got it now.Maybe you can help again.I am typing the following code to draw a QQ plot but the line does not look right?*******************qqnorm(cbiomass)qqline(cbiomass) ***********************the graph looks very different from the graph generated by SAS.Thank you again.Emiliano.Date: Fri, 22 Jan 2010 21:32:26 -0800From: [hidden email] To: [hidden email]Subject: Re: Quartiles and Inter-Quartile Range It's looks like you think that type=2 are the 'true' quantiles, but the default method in R is type=7 You might want to look at ?stats::quantile hth david freedman View message @ http://n4.nabble.com/Quartiles-and-Inter-Quartile-Range-tp1145817p1213199.html To unsubscribe from Quartiles and Inter-Quartile Range, click here. Quer fazer um álbum íncrivel? Conheça o Windows Live Fotos clicando aqui. View message @ http://n4.nabble.com/Quartiles-and-Inter-Quartile-Range-tp1145817p1289588.html To unsubscribe from Re: Quartiles and Inter-Quartile Range, click here. -- Natalia and/or David