Re: [R] QQplot normally distributed

2012-06-20 Thread Noor.v.d.Assem
Hi See the file http://www.mijnbestand.nl/Bestand-6ZPTBYDLBZQI.txt here . That file contains the results of a study on breathing resistance in children with asthma and children with cystic fibrosis to investigate wheter there is a relationship between breathing resistance and length in each of th

Re: [R] QQplot normally distributed

2012-06-20 Thread Noor.v.d.Assem
Hi, So in my example, I can say that the data comes from a moderate normal distribution because the points more at the right lay straight to a straight line, then the points at the left. Please a confirmation here. But what is the information above (that the data is from a normal distribution) say

Re: [R] QQplot normally distributed

2012-06-19 Thread Liviu Andronic
Dear Özgür On Wed, Jun 20, 2012 at 7:37 AM, Özgür Asar wrote: > Why do you prefer robust methods in the example of Noor and why you need > exact normality here? > The idea is that when you do hypothesis testing to check whether a given distribution is normal, the results are rarely informative:

Re: [R] QQplot normally distributed

2012-06-19 Thread Özgür Asar
>Hi, >So in my example, I can say that the data comes from a moderate normal distribution because the points more at the >right lay straight to a straight line, then the points at the left. Please a confirmation here. >But what is the information above (that the data is from a normal distribution)

Re: [R] QQplot normally distributed

2012-06-19 Thread Özgür Asar
Dear Liviu , Why do you prefer robust methods in the example of Noor and why you need exact normality here? Ozgur -- View this message in context: http://r.789695.n4.nabble.com/QQplot-normally-distributed-tp4633819p4633919.html Sent from the R help mailing list archive at Nabble.com. _

Re: [R] QQplot normally distributed

2012-06-19 Thread John Fox
Dear Kjetil, Simulated point-wise confidence envelopes are available from qqPlot() only for studentized residuals from linear and generalized linear models. For an independent sample of observations, the confidence envelopes produced by qqPlot() are based on the standard errors of the order sta

Re: [R] QQplot normally distributed

2012-06-19 Thread Kjetil Halvorsen
Or uou can try library(car) ?qqPlot use that with argument simulate=TRUE, which will give a simulated envelope around the curve for comparison. Kjetil On Tue, Jun 19, 2012 at 9:30 AM, Özgür Asar wrote: > Hi, > > Try boxplot for outliers. > > To decide whether they influence significantly, try

Re: [R] QQplot normally distributed

2012-06-19 Thread Noor.v.d.Assem
Hi, But what are the functions of the outliers on the left and right? Does they influence the normal distribution? -- View this message in context: http://r.789695.n4.nabble.com/QQplot-normally-distributed-tp4633819p4633823.html Sent from the R help mailing list archive at Nabble.com. _

Re: [R] QQplot normally distributed

2012-06-19 Thread Liviu Andronic
On Tue, Jun 19, 2012 at 12:42 PM, Özgür Asar wrote: > Following a straight line indicates less evidence towards non-normality. But > QQ-Plot is an exploratory tool. > > You can confirm your ideas obtained from the QQ-Plot via noramlity tests > such as Shapiro-Wilk test. > Hmm, some gurus on this

Re: [R] QQplot normally distributed

2012-06-19 Thread Özgür Asar
Hi, Try boxplot for outliers. To decide whether they influence significantly, try confirmatory normality tests. Ozgur -- View this message in context: http://r.789695.n4.nabble.com/QQplot-normally-distributed-tp4633819p4633830.html Sent from the R help mailing list archive at Nabble.com.

Re: [R] QQplot normally distributed

2012-06-19 Thread Özgür Asar
Hi, Following a straight line indicates less evidence towards non-normality. But QQ-Plot is an exploratory tool. You can confirm your ideas obtained from the QQ-Plot via noramlity tests such as Shapiro-Wilk test. See shapiro.test under stats package and nortest package. Ozgur -- View this mes