Thursday, August 25, 2005

SPSS User Group Meeting

The SPSS User Group Annual Conference will be held in York in November this year. Diana Kornbrot will be talking about presenting results in logistic regression.

posted by J @ 10:22 AM 0 Comments  

Wednesday, August 24, 2005

Longitudinal multilevel models in SPSS

In Version 11, SPSS added a multilevel modelling (they call it mixed models) procedure. I find the menus completely incomprehensible - I've tried intelligently selecting the appropriate options, and I've tried randomly guessing, and neither gives me the right answer.
Instead, you have to use syntax - and so here, to get you (and me) started, is the syntax for longitudinal multilevel models in SPSS.
I'm assuming you've a variable called time, which represents, well, time. A variable called outcome, which represents the outcome, and a variable called subject, this is (you've guessed it) the subjects.

Your data will look something like:

Time Outcome Subject

1 10 1
2 12 1
3 15 1
1 11 2
2 15 2
2 14 3
3 17 3

...

3 18 200

If you only want random intercepts:

MIXED
outcome with time
/random = intercept | subject (id)
/print = solution.

For random intercepts and slopes, with a zero correlation between slope and intercept):

MIXED
outcome with time
/fixed = time
/random = intercept time | subject (id)
/print = solution.


(Note that the (id) specifies the form of the correlation matrix - id is short for identity.

And for random slope, random intercepts, and correlation between slope and intercept:

MIXED
outcome with time
/fixed = time
/random = intercept time | subject (id) covtype (un)
/print = solution.


The covtype (un) is unstructured.

A much more detailed and useful guide to mixed models in SPSS, written by Alastair Leyland, can be found here.

posted by J @ 9:28 PM 0 Comments  

Wednesday, August 10, 2005

Extrapolating too far

I came across a great example of extrapolation beyond the data, on the medstats mailing list.

It's about how to cook a turkey, by dropping it out of the window. Lots of times. I did a bit of googling, but I couldn't find any other reference to it. The link in medstats is here. If you know more, email me.

Incidentally, the Journal of Irreproducible Results became the Annals of Improbable Research.

posted by J @ 10:35 PM 0 Comments  

Tuesday, August 09, 2005

Website updates

Some updates have been made to the website. The front page http://www.jeremymiles.co.uk/ has been updated. Errors and omissions has been updated. Further reading has been updated, with a couple of new books, and new editions of some books.

posted by J @ 1:45 PM 0 Comments  

Introducing the Blog

This is the Applying Regression blog, which is going to contain stuff about updates to the book Applying Regression and Correlation, by Jeremy Miles and Mark Shevlin.

More information on the book.

posted by J @ 11:17 AM 0 Comments