David.
On Jan 11, 2011, at 3:18 PM, Christofer Bogaso wrote:
> Dear all, I would like to ask one question related to statistics, for
> specifically on defining dummy variables. As of now, I have come
> across 3
> different kind of dummy variables (assuming I am working with Seasonal
> dummy, and number of season is 4):
>
>> dummy1 <- diag(4)
>> for(i in 1:3) dummy1 <- rbind(dummy1, diag(4))
>> dummy1 <- dummy1[,-4]
>>
>> dummy2 <- dummy1
>> dummy2[dummy2 == 0] = -1/(4-1)
>>
>> dummy3 <- dummy1 - 1/4
>>
>> head(dummy1)
> [,1] [,2] [,3]
> [1,] 1 0 0
> [2,] 0 1 0
> [3,] 0 0 1
> [4,] 0 0 0
> [5,] 1 0 0
> [6,] 0 1 0
>> head(dummy2)
> [,1] [,2] [,3]
> [1,] 1.0000000 -0.3333333 -0.3333333
> [2,] -0.3333333 1.0000000 -0.3333333
> [3,] -0.3333333 -0.3333333 1.0000000
> [4,] -0.3333333 -0.3333333 -0.3333333
> [5,] 1.0000000 -0.3333333 -0.3333333
> [6,] -0.3333333 1.0000000 -0.3333333
>> head(dummy3)
> [,1] [,2] [,3]
> [1,] 0.75 -0.25 -0.25
> [2,] -0.25 0.75 -0.25
> [3,] -0.25 -0.25 0.75
> [4,] -0.25 -0.25 -0.25
> [5,] 0.75 -0.25 -0.25
> [6,] -0.25 0.75 -0.25
> Now I want to know which type of dummy definition is called Centered
> dummy
> and why it is called so? Is it equivalent to use any of the above
> definitions (atleast 2nd and 3rd?) It would really be very helpful if
> somebody point any suggestion and clarification.
>
> Thanks and regards,
>
> [[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT