This is similar to what can be done via the Conditions editor, but EM lets you easily specify much more complex and powerful criteria (and lets you use the variable name rather than SGQA naming).
It is only asked if the person first enters their height and weight. Note that you do not use the curly braces when you enter a Relevance Equation. The first page asks how many people live with you and stores that in the "cohabs" variable.This page is only shown if you have more than one cohabitant (so it is shown for the second person cohabitating with you), and also only shows if you specified how Person One is related to you (p1_rel). EM combines the Group and Question-level relevance for you.As you can see, the group also has question-level relevance criteria, such that each question only appears once you have answered the question before it (e.g. Questions in a group are only asked if the group as a whole is relevant. Other times you need even more complex substitution (such as based upon a mathematical computation).Expression Manager (EM) provides an intuitive way to specifying the logic for each of those features.Nearly anything that you can write as a standard mathematical equation is a valid expression, even if you are calling functions.
EM currently provides access to 70 functions, and can be easily extended to support more.
It also lets you access your variables using human-readable variable names (rather than SGQA names).
The following sections show the main places where Expression Manager is used Some surveys use "Goto Logic", such that if you answer Question 1 with option C, then jump to Question 5.
This approach is very limiting, since is hard to validate, and easily breaks if you have to re-order questions.
EM uses a Boolean relevance equation to specify all of the conditions under which a question might be valid.
If the question is relevant, then the question is asked, otherwise it is Not Applicable, and the value NULL is stored in the database.