In SPSS, the reference category is chosen by alphabetic order. So, change the middle category records to make them starting for example by A, or 1.

Hello, Sudesh Pandit . Two ways for you. One is as same as Ahmed Jaber say; the other is creating dummy variables using TRANSFORM in SPSS, select all dummy variables into the model except for the reference group. Hope you can success.

Hi Sudesh,

It sounds like you are using the SPSS graphical user interface (GUI) to generate your Logistic Regression analyses. If this is the case, when you are ready to run the analysis, choose Paste instead of OK. Doing so will generate syntax that looks something like this:

LOGISTIC REGRESSION VARIABLES FATAL_INJ

/METHOD=ENTER SEATBELT

/CONTRAST (SEATBELT)=Indicator

/CRITERIA=PIN(.05) POUT(.10) ITERATE(20) CUT(.5).

Note the /CONTRAST line.

If you choose Last in the GUI the contrast line will appear exactly as above. The default referent category in SPSS for Logistic Regression is the last.

However, if you choose First, the contrast line will look like this:

/CONTRAST (SEATBELT)=Indicator(1)

Where the (1) indicates the FIRST category (and not the category with a value of 1).

If you want to change your reference category, simply change the number in the brackets. Just keep in mind it is the category order and not the category value that you are specifying. For example, lets say I assigned the following codes to SEATBELT:

0 = No Seatbelt

1 = Shoulder

2 = Lap

3 Shoulder and Lap

If I wanted 'No Seatbelt' to be the referent category I would place a '1' in the CONTRAST bracket. If I wanted 'Shoulder', a '2', 'Lap' a '3', and Shoulder and Lap a '4' or I could simply omit the bracket altogether since this is the last category and therefore the SPSS default.

Take care,

Sach

PS: Once you've run your SPSS Logistic Regression syntax, you can visually confirm each of the selected reference categories in your SPSS output by looking at the 'Categorical Variables Codings' table. Whichever category has zeros across its entire Parameter coding row is the referent.