Re: [R] aov and Error function
On 02 Feb 2015, at 13:09 , S Ellison s.elli...@lgcgroup.com wrote:
aovsubj - aov(value~group+time+Error(subject),data=dataRMANOVA)
and
aovsubjgroup - aov(value~group+time+Error(subject/group),data=dataRMANOVA)
Since no-one else seems to have answered you let me point out that your first
formulation treats subject 1 in the int group as being the same as subject
1 in
the cont group, and similarly for subject 2 and so on.
The second formulation (subject nested within group) treats subject 1 in the
int group as being *different* from subject 1 in the cont group.
Yes, but that isn't all, is it?
subject/group
means group nested in subject, expanding to
~subject+subject:group.
so Error(subject/group) asks for a subject effect across groups _as well as_
one within groups.
Or maybe more usefully stated, a group effect within subjects. This could be
relevant if each individual goes to two different groups labeled say 1 and 2,
but the groups are not related between different subjects (subj.1 attends AA
and Boy Scouts, subj 2 School Board and Church, etc.) so there is no main
effect of group. In statistics, it is usually the other way around: subjects
arbitrarily numbered 1-20 within each group, but no relation between subj.1
in one group and subj.2 of the other, in which case ~group +
Error(group:subject) makes sense.
S Ellison
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Re: [R] aov and Error function
aovsubj - aov(value~group+time+Error(subject),data=dataRMANOVA)
and
aovsubjgroup - aov(value~group+time+Error(subject/group),data=dataRMANOVA)
Since no-one else seems to have answered you let me point out that your first
formulation treats subject 1 in the int group as being the same as subject
1 in
the cont group, and similarly for subject 2 and so on.
The second formulation (subject nested within group) treats subject 1 in the
int group as being *different* from subject 1 in the cont group.
Yes, but that isn't all, is it?
subject/group
means group nested in subject, expanding to
~subject+subject:group.
so Error(subject/group) asks for a subject effect across groups _as well as_
one within groups.
S Ellison
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Re: [R] aov and Error function
On 01/02/15 02:17, John Sorkin wrote: I am trying to understand the Error function and its use in ANOVA. In particular I want to understand the difference between two models that differ only with respect to the Error statement: aovsubj - aov(value~group+time+Error(subject),data=dataRMANOVA) and aovsubjgroup - aov(value~group+time+Error(subject/group),data=dataRMANOVA) You will note that in my data I have two subject identifiers, subject and subject2. I am also trying to trying to understand how I should identify subjects, within group (i.e. intervention vs. control) or within time (0=baseline, 1=post) Since no-one else seems to have answered you let me point out that your first formulation treats subject 1 in the int group as being the same as subject 1 in the cont group, and similarly for subject 2 and so on. The second formulation (subject nested within group) treats subject 1 in the int group as being *different* from subject 1 in the cont group. If you were using subject2 instead of subject there would (I *think*) be no difference between the two formulations. HTH cheers, Rolf Turner -- Rolf Turner Technical Editor ANZJS Department of Statistics University of Auckland Phone: +64-9-373-7599 ext. 88276 Home phone: +64-9-480-4619 __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
[R] aov and Error function
I am trying to understand the Error function and its use in ANOVA. In particular I want to understand the difference between two models that differ only with respect to the Error statement: aovsubj- aov(value~group+time+Error(subject),data=dataRMANOVA) and aovsubjgroup-aov(value~group+time+Error(subject/group),data=dataRMANOVA) You will note that in my data I have two subject identifiers, subject and subject2. I am also trying to trying to understand how I should identify subjects, within group (i.e. intervention vs. control) or within time (0=baseline, 1=post) dataRMANOVA value time group subject subject2 1 1.000 int 11 2 2.000 int 22 3 3.000 int 33 4 4.000 int 44 5 5.000 int 55 6 6.000 int 66 7 7.000 int 77 8 8.000 int 88 9 9.000 int 99 10 10.000 int 10 10 11 11.000 int 11 11 12 12.000 int 12 12 13 13.000 int 13 13 14 14.000 int 14 14 15 15.000 int 15 15 16 16.000 int 16 16 17 17.000 int 17 17 18 18.000 int 18 18 19 19.000 int 19 19 20 20.000 int 20 20 21 21.000 cont 1 21 22 22.000 cont 2 22 23 23.000 cont 3 23 24 24.000 cont 4 24 25 25.000 cont 5 25 26 26.000 cont 6 26 27 27.000 cont 7 27 28 28.000 cont 8 28 29 29.000 cont 9 29 30 30.000 cont 10 30 31 31.000 cont 11 31 32 32.000 cont 12 32 33 33.000 cont 13 33 34 34.000 cont 14 34 35 35.000 cont 15 35 36 36.000 cont 16 36 37 37.000 cont 17 37 38 38.000 cont 18 38 39 39.000 cont 19 39 40 40.000 cont 20 40 41 2.8791311 int 11 42 1.5336511 int 22 43 2.4877561 int 33 44 3.4460681 int 44 45 5.1798541 int 55 46 5.7758191 int 66 47 6.9239791 int 77 48 8.1637341 int 88 49 9.5459741 int 99 50 8.7921861 int 10 10 51 11.6575031 int 11 11 52 12.6813931 int 12 12 53 15.0586881 int 13 13 54 13.7576731 int 14 14 55 15.4590291 int 15 15 56 15.5355491 int 16 16 57 16.4332371 int 17 17 58 17.2473301 int 18 18 59 19.0619271 int 19 19 60 21.1650031 int 20 20 61 20.4367051 cont 1 21 62 23.1432301 cont 2 22 63 23.4569461 cont 3 23 64 23.1322841 cont 4 24 65 24.9020171 cont 5 25 66 26.4503991 cont 6 26 67 27.3569431 cont 7 27 68 27.4020231 cont 8 28 69 29.7598831 cont 9 29 70 27.9696281 cont 10 30 71 30.0614751 cont 11 31 72 32.5324271 cont 12 32 73 33.3788771 cont 13 33 74 34.8522441 cont 14 34 75 34.9585941 cont 15 35 76 35.6732251 cont 16 36 77 37.9082081 cont 17 37 78 37.9824711 cont 18 38 79 39.0169171 cont 19 39 80 39.5075831 cont 20 40 Thank you, John John David Sorkin M.D., Ph.D. Professor of Medicine Chief, Biostatistics and Informatics University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax) 410-605-7913 (Please call phone number above prior to faxing) Confidentiality Statement: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
