6 messages · emj83, Mark Difford
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p24954045.html Sent from the R help mailing list archive at Nabble.com.
can anyone advise me please?
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25120522.html Sent from the R help mailing list archive at Nabble.com.
Hi Emma,
R gives you the tools to work this out.
## Example
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
with(TDat, boxplot(split(response, group)))
summary(aov(response ~ group, data=TDat))
Regards, Mark.
can anyone advise me please? emj83 wrote:
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25121532.html Sent from the R help mailing list archive at Nabble.com.
I have done this in R and this is the following ANOVA table I get:
summary(aov(response ~ group, data=TDat))
Df Sum Sq Mean Sq F value Pr(>F) group 1 11203.5 11203.5 2505.0 < 2.2e-16 *** Residuals 198 885.5 4.5 The model is response(i,j)= group(i)+ error(i,j), we assume that group~N(0,P^2) and error~N(0,sigma^2) I know that sigma^2 is equal to 4.5, how do I find out P^2? In the problem that I am trying to apply this to, I have more than 2 groups. I was hoping there would be a function that helps you do this that I don't know about. Thanks for your help Emma
Hi Emma,
R gives you the tools to work this out.
## Example
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
with(TDat, boxplot(split(response, group)))
summary(aov(response ~ group, data=TDat))
Regards, Mark.
emj83 wrote:
can anyone advise me please? emj83 wrote:
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25122960.html Sent from the R help mailing list archive at Nabble.com.
Hi Emma,
...from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance?
But it's in the table, above the "within-group" variance. Remember that F is
the ratio of these two quantities, i.e. the mean of the group variances
divided by the mean of the within-group variances . I will work with my
example since you never set seed so your answers are different from mine
(which really does not help matters).
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
summary(aov(response ~ group, data=TDat))
11225.25/3.64
[1] 3083.86
There is some rounding error on the mean squares (i.e. mean variances) but F
is correct. Using estimates calculated by a different route we have:
11225.249057/3.639801
[1] 3084.028
Does this answer your question?
Regards, Mark.
I have done this in R and this is the following ANOVA table I get:
summary(aov(response ~ group, data=TDat))
Df Sum Sq Mean Sq F value Pr(>F) group 1 11203.5 11203.5 2505.0 < 2.2e-16 *** Residuals 198 885.5 4.5 The model is response(i,j)= group(i)+ error(i,j), we assume that group~N(0,P^2) and error~N(0,sigma^2) I know that sigma^2 is equal to 4.5, how do I find out P^2? In the problem that I am trying to apply this to, I have more than 2 groups. I was hoping there would be a function that helps you do this that I don't know about. Thanks for your help Emma Mark Difford wrote:
Hi Emma,
R gives you the tools to work this out.
## Example
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
with(TDat, boxplot(split(response, group)))
summary(aov(response ~ group, data=TDat))
Regards, Mark.
emj83 wrote:
can anyone advise me please? emj83 wrote:
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25129942.html Sent from the R help mailing list archive at Nabble.com.
Hi Emma,
...
I forgot to add the tabular ouput, which doesn't help either:
T.sum <- summary(aov(response ~ group, data=TDat))
print(T.sum)
Df Sum Sq Mean Sq F value Pr(>F)
group 1 11225.2 11225.2 3084 < 2.2e-16 ***
Residuals 198 720.7 3.6
---
Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1
unlist(T.sum)
unlist(T.sum)[5]/unlist(T.sum)[6]
Mean Sq1
3084.028
Regards, Mark.
Hi Emma,
...from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance?
But it's in the table, above the "within-group" variance. Remember that F
is the ratio of these two quantities, i.e. the mean of the group variances
divided by the mean of the within-group variances . I will work with my
example since you never set seed so your answers are different from mine
(which really does not help matters).
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
summary(aov(response ~ group, data=TDat))
11225.25/3.64
[1] 3083.86
There is some rounding error on the mean squares (i.e. mean variances) but
F is correct. Using estimates calculated by a different route we have:
11225.249057/3.639801
[1] 3084.028
Does this answer your question?
Regards, Mark.
emj83 wrote:
I have done this in R and this is the following ANOVA table I get:
summary(aov(response ~ group, data=TDat))
Df Sum Sq Mean Sq F value Pr(>F) group 1 11203.5 11203.5 2505.0 < 2.2e-16 *** Residuals 198 885.5 4.5 The model is response(i,j)= group(i)+ error(i,j), we assume that group~N(0,P^2) and error~N(0,sigma^2) I know that sigma^2 is equal to 4.5, how do I find out P^2? In the problem that I am trying to apply this to, I have more than 2 groups. I was hoping there would be a function that helps you do this that I don't know about. Thanks for your help Emma Mark Difford wrote:
Hi Emma,
R gives you the tools to work this out.
## Example
set.seed(7)
TDat <- data.frame(response = c(rnorm(100, 5, 2), rnorm(100, 20, 2)))
TDat$group <- gl(2, 100, labels=c("A","B"))
with(TDat, boxplot(split(response, group)))
summary(aov(response ~ group, data=TDat))
Regards, Mark.
emj83 wrote:
can anyone advise me please? emj83 wrote:
I have done some ANOVA tables for some data that I have, from this I can read the within-group variance. can anyone tell me how i may find out the between-group variance? Thanks Emma
View this message in context: http://www.nabble.com/Between-group-variance-from-ANOVA-tp24954045p25130266.html Sent from the R help mailing list archive at Nabble.com.