15 oct. 2012

Equations with indicator variables - part 1


Sometimes it is necessary to merge spectra files from different instruments (standardized or not) to get a bigger data base with more variability, range,…
We would like that all the laboratory values would come from the same lab, but this is not normally the case, and the lab data comes from different labs (probably one for each instrument). In that case we can add some indicator variables to help on this to the software.
Suppose we have 2 spectra files, one from one instrument (1) with lab values from Lab1, and  the other from a different instrument (2) with lab values from Lab2. In this case we create an indicator variable adding “ceros”  for the instrument 1_lab1 spectra:
0
0
0
And “ones” to the instrument2_ lab2 spectra :
1
1
1
In the case of three instruments, three labs, we would need 2 indicator variables:
For instrument 1_lab1:
0          0
0          0         
0          0         
For instrument 2_lab2:
1          0
1          0         
1          0
For instrument 3_lab3:
0          1
0          1         
0          1
In the case of 4 instruments, four labs, we would need 3 indicator variables:
For instrument 1_lab1:
0          0          0
0          0          0
0          0          0
For instrument 2_lab2:
1          0          0
1          0          0
1          0          0
For instrument 3_lab3:
0          1          0
0          1          0
0          1          0
For instrument 4_lab4:
0          0          1
0          0          1
0          0          1
And so on,
Of course we can use this method for only one instrument with lab data from four labs, so in this case it will be:
Instrument 1_lab1, instrument 1_lab2, instrument 1_lab3 and instrument 1_lab4

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