[R] aov and Error function

[John Sorkin]

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   1.000000    0   int       1        1
2   2.000000    0   int       2        2
3   3.000000    0   int       3        3
4   4.000000    0   int       4        4
5   5.000000    0   int       5        5
6   6.000000    0   int       6        6
7   7.000000    0   int       7        7
8   8.000000    0   int       8        8
9   9.000000    0   int       9        9
10 10.000000    0   int      10       10
11 11.000000    0   int      11       11
12 12.000000    0   int      12       12
13 13.000000    0   int      13       13
14 14.000000    0   int      14       14
15 15.000000    0   int      15       15
16 16.000000    0   int      16       16
17 17.000000    0   int      17       17
18 18.000000    0   int      18       18
19 19.000000    0   int      19       19
20 20.000000    0   int      20       20
21 21.000000    0  cont       1       21
22 22.000000    0  cont       2       22
23 23.000000    0  cont       3       23
24 24.000000    0  cont       4       24
25 25.000000    0  cont       5       25
26 26.000000    0  cont       6       26
27 27.000000    0  cont       7       27
28 28.000000    0  cont       8       28
29 29.000000    0  cont       9       29
30 30.000000    0  cont      10       30
31 31.000000    0  cont      11       31
32 32.000000    0  cont      12       32
33 33.000000    0  cont      13       33
34 34.000000    0  cont      14       34
35 35.000000    0  cont      15       35
36 36.000000    0  cont      16       36
37 37.000000    0  cont      17       37
38 38.000000    0  cont      18       38
39 39.000000    0  cont      19       39
40 40.000000    0  cont      20       40
41  2.879131    1   int       1        1
42  1.533651    1   int       2        2
43  2.487756    1   int       3        3
44  3.446068    1   int       4        4
45  5.179854    1   int       5        5
46  5.775819    1   int       6        6
47  6.923979    1   int       7        7
48  8.163734    1   int       8        8
49  9.545974    1   int       9        9
50  8.792186    1   int      10       10
51 11.657503    1   int      11       11
52 12.681393    1   int      12       12
53 15.058688    1   int      13       13
54 13.757673    1   int      14       14
55 15.459029    1   int      15       15
56 15.535549    1   int      16       16
57 16.433237    1   int      17       17
58 17.247330    1   int      18       18
59 19.061927    1   int      19       19
60 21.165003    1   int      20       20
61 20.436705    1  cont       1       21
62 23.143230    1  cont       2       22
63 23.456946    1  cont       3       23
64 23.132284    1  cont       4       24
65 24.902017    1  cont       5       25
66 26.450399    1  cont       6       26
67 27.356943    1  cont       7       27
68 27.402023    1  cont       8       28
69 29.759883    1  cont       9       29
70 27.969628    1  cont      10       30
71 30.061475    1  cont      11       31
72 32.532427    1  cont      12       32
73 33.378877    1  cont      13       33
74 34.852244    1  cont      14       34
75 34.958594    1  cont      15       35
76 35.673225    1  cont      16       36
77 37.908208    1  cont      17       37
78 37.982471    1  cont      18       38
79 39.016917    1  cont      19       39
80 39.507583    1  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) 


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