Number of subjects = 25 Mean of Sample = 77 Standard Deviation (s) = 12 sem = 2.4 df = 24 The claim is that population mean is less than 80 * > 80 So our H0 (null hupotheis) is * > 80> qt(.95,24)[1] 1.710882> qt(0.05, 24)[1] -1.710882 tstat = -1.25 on t24 falls between 1.711 (.95,24) and *1.711 (.005,24) How Could I sketch t curve for the above data where my * would be at the center? Best Regards Isaac Dr. I. Barjis Assistant Professor Summer and Evening Coordinator Department of Biological Sciences Room P313 300 Jay Street Brooklyn, NY 11201 Phone: (718)2605285 Fax: (718)2548680 Fax: (718) 254-8595 Department Office http://websupport1.citytech.cuny.edu/Faculty/ibarjis -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: Isaac Barjis.vcf Url: https://stat.ethz.ch/pipermail/r-help/attachments/20060927/f9c3c876/attachment.pl
> -----Original Message----- > From: r-help-bounces at stat.math.ethz.ch [mailto:r-help- > bounces at stat.math.ethz.ch] On Behalf Of Isaac Barjis > Sent: Wednesday, September 27, 2006 8:08 AM > To: R-help at stat.math.ethz.ch > Subject: [R] t-stat Curve > > Number of subjects = 25 > Mean of Sample = 77 > Standard Deviation (s) = 12 > sem = 2.4 > df = 24 > > The claim is that population mean is less than 80 > * > 80 > So our H0 (null hupotheis) is * > 80 > > > > qt(.95,24) > [1] 1.710882 > > qt(0.05, 24) > [1] -1.710882 > > tstat = -1.25 on t24 falls between 1.711 (.95,24) and *1.711 (.005,24) > > > How Could I sketch t curve for the above data where my * would be at the > center? > > Best Regards > Isaac > > Dr. I. Barjis > Assistant Professor > Summer and Evening Coordinator > Department of Biological SciencesIsaac, I'm not sure that what you are asking for is reasonable (or possible). It is the sampling distribution of your t-statistic that is distributed as t under the null hypothesis, not your observed data. Could you clarify what it is you wish to do? Dan Daniel J. Nordlund Research and Data Analysis Washington State Department of Social and Health Services Olympia, WA 98504-5204
Isaac:
You will likely find something helpful here:
http://addictedtor.free.fr/graphiques/thumbs.php
I also recently came across this code (I thought it was at the URL above,
but I can't find it now) that may be useful with modification.
I apologize to the code-writer for having lost the correct reference. (If
anyone finds it, please send the reference to me. Thanks.)
#########################################
# neighboring (not "overlapping") normal densities
dev.off()
x<-seq(-10,10,length=400)
y1<-dnorm(x)
y2<-dnorm(x,m=3)
par(mar=c(5,4,2,1))
plot(x, y2, xlim=c(-3,8), type="n", xlab=quote(Z==frac(mu[1]-mu[2],
sigma/sqrt(n))), ylab="Density")
polygon(c(1.96,1.96,x[240:400],10), c(0,dnorm(1.96,m=3),y2[240:400],0),
col="grey80", lty=0)
lines(x, y2)
lines(x, y1)
polygon(c(-1.96,-1.96,x[161:1],-10), c(0,dnorm(-1.96,m=0), y1[161:1],0),
col="grey30", lty=0)
polygon(c(1.96, 1.96, x[240:400], 10), c(0,dnorm(1.96,m=0),
y1[240:400],0), col="grey30")
legend(4.2, .4, fill=c("grey80","grey30"),
legend=expression(P(abs(phantom(i)*Z*phantom(i))>1.96,
H[1])==0.85,
P(abs(phantom(i)*Z*phantom(i))>1.96,H[0])==0.05),
bty="n")
text(0, .2, quote(H[0]:~~mu[1]==mu[2]))
text(3, .2, quote(H[1]:~~mu[1]==mu[2]+delta))
#########################################
Charles Annis, P.E.
Charles.Annis at StatisticalEngineering.com
phone: 561-352-9699
eFax: 614-455-3265
http://www.StatisticalEngineering.com
-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Isaac Barjis
Sent: Wednesday, September 27, 2006 11:08 AM
To: R-help at stat.math.ethz.ch
Subject: [R] t-stat Curve
Number of subjects = 25
Mean of Sample = 77
Standard Deviation (s) = 12
sem = 2.4
df = 24
The claim is that population mean is less than 80
* > 80
So our H0 (null hupotheis) is * > 80
> qt(.95,24)
[1] 1.710882> qt(0.05, 24)
[1] -1.710882
tstat = -1.25 on t24 falls between 1.711 (.95,24) and *1.711 (.005,24)
How Could I sketch t curve for the above data where my * would be at the
center?
Best Regards
Isaac
Dr. I. Barjis
Assistant Professor
Summer and Evening Coordinator
Department of Biological Sciences
Room P313
300 Jay Street
Brooklyn, NY 11201
Phone: (718)2605285
Fax: (718)2548680
Fax: (718) 254-8595 Department Office
http://websupport1.citytech.cuny.edu/Faculty/ibarjis
## There is some ambiguity in your example.
## You stated a one-sided hypothesis and calculated qt() values for both sides.
## I show both the one-sided and two-sided displays.
library(HH)
## HH_1.5 is available from CRAN for R-2.3.1
##
## HH_1.5 ignores the df.t argument and interprets the request as a
## normal distribution.
## HH_1.8 has been accepted for CRAN for R-2.4.0 and will be in the
## standard places on CRAN when R-2.4.0 is released.
##
## HH_1.8 uses the df.t argument and interprets the request as a
## t-distribution.
old.par <- par(oma=c(4,0,2,5), mar=c(7,7,4,2)+.1)
crit.val.t <- qt(c(.05,.95), 24)
crit.val <- crit.val.t*(12/sqrt(25)) + 80
observed.t <- -1.25
observed.ybar <- 77
norm.setup(mean=80, n=25, sd=12, df.t=24, xlim=c(70,90),
main="two-sided alpha=.10")
norm.curve(mean=80, n=25, sd=12, df.t=24, crit=crit.val)
abline(v=observed.ybar)
axis(side=3, at=observed.ybar, line=-.5)
norm.setup(mean=80, n=25, sd=12, df.t=24, xlim=c(70,90),
main="one-sided alpha=.05")
norm.curve(mean=80, n=25, sd=12, df.t=24, crit=crit.val[1],
shade="left")
abline(v=observed.ybar)
axis(side=3, at=observed.ybar, line=-.5)
par(old.par)