Effects coding in SurveyEngine

Experiments
1

Hi, I was trying to import an experimental design generated in Ngene into SurveyEngine. However, I noticed that the SurveyEngine Design Template requires the attribute levels to start from 0.

My design uses effects coding, so some levels are coded as -1 rather than starting from 0. I wonder whether SurveyEngine supports effects-coded designs. And how should I format the design file when some attribute levels are coded as -1?

Thanks!

2

Rui,
The experiment design are always offsets from zero. Which is the same as saying dummy coded with the first level being 0.
Effects coding are not supported so you’ll need to adjust your design accordingly.
however this is a trivial operation that can be done in excel through re-mapping levels.
There are a couple of reasons dummy coding is used more

  1. it’s more readable and auditable
  2. it’s used as a standard in Ngene and Apollo
  3. there are (provably) no advantages in modelling using effects coding - although in older papers it was incorrectly stated so.

It depends on what your base level is and how your design is structured.

So you will typically have for a k-level attribute k-1 columns. These k-1 columns need to be collapsed into 1 column for each attribute.

So for example if you have a 4 level attribute your factorial effects design would be

1 0 0
0 1 0
0 0 1
-1 -1 -1

This needs to be mapped to

(1 0 0) →0
(0 1 0)→1
(0 0 1) →2
(-1 -1 -1) →3

But it depends where your base level is.