Displaying 20 results from an estimated 10000 matches similar to: "estimating treatment effect in blocked experiment"
2003 Jul 30
2
Comparing two regression slopes
Hello,
I've written a simple (although probably overly roundabout) function to
test whether two regression slope coefficients from two linear models on
independent data sets are significantly different. I'm a bit concerned,
because when I test it on simulated data with different sample sizes and
variances, the function seems to be extremely sensitive both of these. I am
wondering if
2005 Aug 12
1
as.formula and lme ( Fixed effects: Error in as.vector(x, "list") : cannot coerce to vector)
This is a continuing issue with the one on the list a long time ago (I
couldn't find a solution to it from the web):
--------------------------------------------------------------------------
> Using a formula converted with as.formula with lme leads
> to an error message. Same works ok with lm, and with
> lme and a fixed formula.
>
> # demonstrates problems with lme and
2001 Feb 23
1
as.formula and lme ( Fixed effects: Error in as.vector(x, "list") : cannot coerce to vector)
Using a formula converted with as.formula with lme leads
to an error message. Same works ok with lm, and with
lme and a fixed formula.
# demonstrates problems with lme and as.formula
demo<-data.frame(x=1:20,y=(1:20)+rnorm(20),subj=as.factor(rep(1:2,10)))
demo.lm1<-lme(y~x,data=demo,random=~1|subj)
print(summary(demo.lm1))
newframe<-data.frame(x=1:5,subj=rep(1,5))
2012 Jul 06
2
Anova Type II and Contrasts
the study design of the data I have to analyse is simple. There is 1 control group (CTRL) and 2 different treatment groups (TREAT_1 and TREAT_2).
The data also includes 2 covariates COV1 and COV2. I have been asked to check if there is a linear or quadratic treatment effect in the data.
I created a dummy data set to explain my situation:
df1 <- data.frame(
Observation =
2003 Feb 01
0
AIC.default (PR#2518)
There is a bug in AIC.default and AIC.lm, as illustrated below.
(I've only checked this under 1.6.1, and can't easily check if it has
already been reported since the site is down.)
> lm1 <- lm(y ~ x, list(x=1:10, y=jitter(1:10)))
> lm2 <- lm(y ~ x, list(x=1:10, y=jitter(1:10)))
> AIC(lm1, lm2)
df AIC
lm1 3 -18.662493
lm2 3 -7.265906
> AIC(lm1, lm2, k = 2)
2012 Jan 13
2
Help needed in interpreting linear models
Dear members of the R-help list,
I have sent the email below to the R-SIG-ME list to ask for help in
interpreting some R output of fitted linear models.
Unfortunately, I haven't yet received any answers. As I am not sure if my
email was sent successfully to the mailing list I
am asking for help here:
Dear members of the R-SIG-ME list,
I am new to linear models and struggling with
2010 Apr 08
2
Overfitting/Calibration plots (Statistics question)
This isn't a question about R, but I'm hoping someone will be willing
to help. I've been looking at calibration plots in multiple regression
(plotting observed response Y on the vertical axis versus predicted
response [Y hat] on the horizontal axis).
According to Frank Harrell's "Regression Modeling Strategies" book
(pp. 61-63), when making such a plot on new data
2006 Mar 10
1
add trend line to each group of data in: xyplot(y1+y2 ~ x | grp...
Although this should be trivial, I'm having a spot of trouble.
I want to make a lattice plot of the format y1+y2 ~ x | grp but then fit a
lm to each y variable and add an abline of those models in different colors.
If the xyplot followed y~x|grp I would write a panel function as below, but
I'm unsure of how to do that with y1 and y2 without reshaping the data
before hand. Thoughts
2007 Aug 06
1
test the significances of two regression lines
R-help,
I'm trying to test the significance of two regression lines
, i.e. the significance of the slopes from two samples
originated from the same population.
Is it correct if I fit a liner model for each sample and
then test the slope signicance with 'anova'. Something like this:
lm1 <- lm(Y~ a1 + b1*X) # sample 1
lm2 <- lm(Y~ a2 + b2*X) # sample 2
anova(lm1, lm2)
2002 Dec 20
1
Printing correlation matrices (lm/glm)
Hi Folks,
I'm analysing some data which, in its simplest aspect,
has 3 factors A, B, C each at 2 levels.
If I do
lm1 <- lm(y ~ A*B)
say, and then
summary(lm1, corr=T)
I get the correlation matrix of the estimated coeffcients
with numerical values for the correlations (3 coeffs in this
case). Likewise with 'glm' instead of 'lm'.
However, if I do
lm2 <- lm(y ~
2003 Oct 28
1
error message in simulation
Dear R-users,
I am a dentist (so forgive me if my question looks stupid) and came across
a problem when I did simulations to compare a few single level and two
level regressions.
The simulations were interrupted and an error message came out like 'Error
in MEestimate(lmeSt, grps) : Singularity in backsolve at level 0, block 1'.
My collegue suggested that this might be due to my codes
2005 Nov 17
1
anova.gls from nlme on multiple arguments within a function fails
Dear All --
I am trying to use within a little table producing code an anova
comparison of two gls fitted objects, contained in a list of such
object, obtained using nlme function gls.
The anova procedure fails to locate the second of the objects.
The following code, borrowed from the help page of anova.gls,
exemplifies:
--------------- start example code ---------------
library(nlme)
##
2010 Jun 17
1
Problems using allEffects() (package effect)
Dear R users,
I have some trouble using the allEffects() function to compute and
display effect plots for a linear model.
My data is quite simple, it concerns effects of 3 treatments on the
tumoral volume of mice. vTum codes for the qualitative initial volume,
from small to big, temps is the time in month since beginning of
treatment, and S?rie codes for the batch. Data is unbalanced.
>
2005 Aug 04
0
add1.lm and add1.glm not handling weights and offsets properly (PR#8049)
I am using R 2.1.1 under Mac OS 10.3.9.
Two related problems (see notes 1. and 2. below) are illustrated by
results of the following:
y <- rnorm(10)
x <- z <- 1:10
is.na(x[9]) <- TRUE
lm0 <- lm(y ~ 1)
lm1 <- lm(y ~ 1, weights = rep(1, 10))
add1(lm0, scope = ~ x) ## works ok
add1(lm1, scope = ~ x) ## error
lm2 <- lm(y ~ 1, offset = 1:10)
add1(lm0, scope = ~ z) ##
2008 Nov 24
3
Is this correct?
I have to answer the following question for a homework assignment.
A researcher was interested in whether people taking part in sports at
university made more money after graduating, taking into account the
students' GPA. They sampled 200 alumni from a large university. The
variables are: income (income 10 years after graduating), sports (1 if they
did sports, 0 if they did not), and GPA (the
2014 Jun 13
3
p values con LMER
Hola Manuel
lo he tratado de hacer pero me sale
Error: unexpected string constante in:
"anova(a,as,test=Chisq")
no tengo ni idea de por qué...
Me resulta alucinante no poder contar ya con pvals.fnc. ¿Será imposible hacerse con ello?
Saludos,
Miguel
--------------------------------------------
El vie, 13/6/14, Manuel Azcárate <mazcarategarcia en gmail.com> escribió:
2005 Aug 05
0
(PR#8049) add1.lm and add1.glm not handling weights and
David,
Thanks.
The reason add1.lm (and drop1.lm) do not support offsets is that lm did
not when they were written, and the person who added offsets to lm did not
change them. (I do wish they had not added an offset arg and just used the
formula as in S's glm.) That is easy to add.
For the other point, some care is needed if 'x' is supplied and the upper
scope reduces the number
2008 Jun 04
1
Comparing two regression lines
Dear R users,
Suppose I have two different response variables y1, y2 that I regress separately on the same
explanatory variable, x; sample sizes are n1=n2.
Is it legitimate to compare the regression slopes (equal variances assumed) by using
lm(y~x*FACTOR),
where FACTOR gets "y1" if y1 is the response, and "y2" if y2 is the response?
The problem I see here is that the
2004 Aug 26
1
Why terms are dropping out of an lm() model
Hi all!
I'm fairly new to R and not too experienced with regression. Because
of one or both of those traits, I'm not seeing why some terms are being
dropped from my model when doing a regression using lm().
I am trying to do a regression on some experimental data d, which has
two numeric predictors, p1 and p2, and one numeric response, r. The aim
is to compare polynomial models in p1
2010 Jul 07
3
Large discrepancies in the same object being saved to .RData
Hi developers,
After some investigation I have found there can be large discrepancies in the same object being saved as an external "xx.RData" file. The immediate repercussion of this is the possible increased size of your .RData workspace for no apparent reason.
The function and its three scenarios below highlight these discrepancies. Note that the object being returned is exactly