Hi Michael,
Thank you for the reply.
I am sorry I forgot to print out the anova table to make my question clear.
Df Sum Sq Mean Sq F value Pr(>F)
S 2 0.000019 9.630e-06 0.818 0.444
x1 1 0.000256 2.560e-04 21.751 9.44e-06 ***
ID 47 0.003524 7.498e-05 6.370 3.35e-15 ***
Resid 102 0.001201 1.177e-05
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
There is *no* unique value for ID for each combination of S and x1. For
example, S=1 and x1=0 can equal to either B or C or D or E or F .
Perhaps you mean that for each combination of S and x1 have different
values. If that is the case, I think maybe it makes sense.
*What I think? *
Anova has this thing where it fits the terms of 1st order first ( a formula
term including no interactions) before it fits a 2nd order term ( a formula
term including 1 interaction) and so on.
First Order--> Second Order--> Third Order--> etc
Therefore, it is known that the true fitting formula is not S+x1+S:x1+ID
but it is S+x1+ID+S:x1. Hence, it appears that ID is fitted before S:x1 but
since ID is a more refined factor than S:x1, it can be said that S:x1 is
already included in the fit of ID so R recognizes the linear dependance and
excludes the term S:x1.
In other words, S:x1 is linearly dependant to ID. And so, the row S:x1
disappears because it is considered within ID.
Does this makes sense?
On 19 July 2016 at 16:19, Michael Dewey <li...@dewey.myzen.co.uk> wrote:
> Presumably it disappears because there is a unique value of ID for eac
> combination of S*x1 so they are indistinguishable.
>
>
> On 19/07/2016 12:53, Justin Thong wrote:
>
>> Why does the S:x1 column disappear (presumably S:x1 goes into ID but I
>> dont
>> know why)? S is a factor, x1 is a covariate and ID is a factor.
>>
>> rich.side<-aov(y~S*x1+ID)
>> summary(rich.side)
>>
>> Below is the model frame
>>
>> model.frame(~S*x1+ID)
>>
>> S x1 ID
>> 1 1 12 A
>> 2 1 12 A
>> 3 1 12 A
>> 4 1 12 A
>> 5 1 0 B
>> 6 1 0 B
>> 7 1 0 B
>> 8 1 0 B
>> 9 1 0 C
>> 10 1 0 C
>> 11 1 0 C
>> 12 1 0 C
>> 13 1 0 D
>> 14 1 0 D
>> 15 1 0 D
>> 16 1 0 D
>> 17 1 0 E
>> 18 1 0 E
>> 19 1 0 E
>> 20 1 0 E
>> 21 1 0 F
>> 22 1 0 F
>> 23 1 0 F
>> 24 1 0 F
>> 25 2 6 AB
>> 26 2 6 AB
>> 27 2 6 AB
>> 28 2 6 AB
>> 29 2 6 AC
>> 30 2 6 AC
>> 31 2 6 AC
>> 32 2 6 AC
>> 33 2 6 AD
>> 34 2 6 AD
>> 35 2 6 AD
>> 36 2 6 AD
>> 37 2 6 AE
>> 38 2 6 AE
>> 39 2 6 AE
>> 40 2 6 AE
>> 41 2 6 AF
>> 42 2 6 AF
>> 43 2 6 AF
>> 44 2 6 AF
>> 45 2 0 BC
>> 46 2 0 BC
>> 47 2 0 BC
>> 48 2 0 BC
>> 49 2 0 BD
>> 50 2 0 BD
>> 51 2 0 BD
>> 52 2 0 BD
>> 53 2 0 BE
>> 54 2 0 BE
>> 55 2 0 BE
>> 56 2 0 BE
>> 57 2 0 BF
>> 58 2 0 BF
>> 59 2 0 BF
>> 60 2 0 BF
>> 61 2 0 CD
>> 62 2 0 CD
>> 63 2 0 CD
>> 64 2 0 CD
>> 65 2 0 CE
>> 66 2 0 CE
>> 67 2 0 CE
>> 68 2 0 CE
>> 69 2 0 CF
>> 70 2 0 CF
>> 71 2 0 CF
>> 72 2 0 CF
>> 73 2 0 DE
>> 74 2 0 DE
>> 75 2 0 DE
>> 76 2 0 DE
>> 77 2 0 DF
>> 78 2 0 DF
>> 79 2 0 DF
>> 80 2 0 DF
>> 81 2 0 EF
>> 82 2 0 EF
>> 83 2 0 EF
>> 84 2 0 EF
>> 85 3 4 ABC
>> 86 3 4 ABC
>> 87 3 4 ABC
>> 88 3 4 ABC
>> 89 3 4 ABD
>> 90 3 4 ABD
>> 91 3 4 ABD
>> 92 3 4 ABD
>> 93 3 4 ABE
>> 94 3 4 ABE
>> 95 3 4 ABE
>> 96 3 4 ABE
>> 97 3 4 ABF
>> 98 3 4 ABF
>> 99 3 4 ABF
>> 100 3 4 ABF
>> 101 3 4 ACD
>> 102 3 4 ACD
>> 103 3 4 ACD
>> 104 3 4 ACD
>> 105 3 4 ACE
>> 106 3 4 ACE
>> 107 3 4 ACE
>> 108 3 4 ACE
>> 109 3 4 ACF
>> 110 3 4 ACF
>> 111 3 4 ACF
>> 112 3 4 ACF
>> 113 3 4 ADE
>> 114 3 4 ADE
>> 115 3 4 ADE
>> 116 3 4 ADE
>> 117 3 4 ADF
>> 118 3 4 ADF
>> 119 3 4 ADF
>> 120 3 4 ADF
>> 121 3 4 AEF
>> 122 3 4 AEF
>> 123 3 4 AEF
>> 124 3 4 AEF
>> 125 3 0 BCD
>> 126 3 0 BCD
>> 127 3 0 BCD
>> 128 3 0 BCD
>> 129 3 0 BCE
>> 130 3 0 BCE
>> 131 3 0 BCE
>> 132 3 0 BCE
>> 133 3 0 BCF
>> 134 3 0 BCF
>> 135 3 0 BCF
>> 136 3 0 BCF
>> 137 3 0 BDE
>> 138 3 0 BDE
>> 139 3 0 BDE
>> 140 3 0 BDE
>> 141 3 0 BDF
>> 142 3 0 BDF
>> 143 3 0 BDF
>> 144 3 0 BDF
>> 145 3 0 BEF
>> 146 3 0 BEF
>> 147 3 0 BEF
>> 148 3 0 BEF
>> 149 3 0 CDE
>> 150 3 0 CDE
>> 151 3 0 CDE
>> 152 3 0 CDE
>> 153 3 0 CDF
>> 154 3 0 CDF
>> 155 3 0 CDF
>> 156 3 0 CDF
>> 157 3 0 CEF
>> 158 3 0 CEF
>> 159 3 0 CEF
>> 160 3 0 CEF
>> 161 3 0 DEF
>> 162 3 0 DEF
>> 163 3 0 DEF
>> 164 3 0 DEF
>>
>>
> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>
--
Yours sincerely,
Justin
*I check my email at 9AM and 4PM everyday*
*If you have an EMERGENCY, contact me at +447938674419(UK) or
+60125056192(Malaysia)*
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