I've always used syntax to create dummy variables and it works the same in PSPP and SPSS.
If you had a categorical variable X with *three* values 0/1/2 you would create *two* dummy coded variables like this: recode x (0=1) (1=0) (2=0) (ELSE=SYSMIS) into x_dum1. recode x (0=0) (1=1) (2=0) (ELSE=SYSMIS) into x_dum2. execute. This creates two dummy variables called x_dum1 and x_dum2 and they encode the effect for category 0 and 1 (respectively) vs. category 2 as a reference. If you wanted to use, say, group 1 as the reference, then you make sure that 1 is encoded as zero for both dummy variables: recode x (0=1) (1=0) (2=0) (ELSE=SYSMIS) into x_dum1. recode x (0=0) (1=0) (2=1) (ELSE=SYSMIS) into x_dum2. execute. Sometimes to give myself more flexibility, I create dummy codes for all three values and only pick two in any analysis. This forces the category of the left out dummy variable to be the reference: recode x (0=1) (1=0) (2=0) (ELSE=SYSMIS) into x_dum0. recode x (0=0) (1=1) (2=0) (ELSE=SYSMIS) into x_dum1. recode x (0=0) (1=0) (2=1) (ELSE=SYSMIS) into x_dum2. execute. For example, if you enter x_dum0 and x_dum2 then category 1 is the reference. If you forget and enter all three dummy variables the regression should fail because the data matrix lacks full rank. -Alan On 9/29/2016 9:58 AM, Jack Drew wrote: > Thanks for the speedy response, Alan. > > To be clear: if memory serves SPSS lets you specify the reference > value for a categorical variable. So for a variable with 0/1/2 > values, you can specify '0' as the reference category. > > However, if I understand you correctly, the method for PSPP is to > create a dummy variable (0/1) for each of the 0/1/2 values and then > exclude the dummy variable for 0 as the reference group. You can run > additional models and swap out the remaining variables to change > reference group. > > Jack -- Alan D. Mead, Ph.D. President, Talent Algorithms Inc. science + technology = better workers +815.588.3846 (Office) +267.334.4143 (Mobile) http://www.alanmead.org I've... seen things you people wouldn't believe... functions on fire in a copy of Orion. I watched C-Sharp glitter in the dark near a programmable gate. All those moments will be lost in time, like Ruby... on... Rails... Time for Pi. --"The Register" user Alister, applying the famous "Blade Runner" speech to software development
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