Question derivation

Not every question has to be filled in by the data entry user. It is possible to set a question to automatically calculate its value from the answer given to another question or number of questions. This is known as derivation. A derived question appears as a read-only field on the eForm during data entry and the derivation is shown on the question menu which is displayed when the data entry user clicks the question status icon.

The Arezzo Terms report in the Study Data Diagnostic Utility module can be used to list all existing derivations in a study definition.

Creating a derived question

To create a derived question, create a question in the normal way and enter an Arezzo expression into the Derivation field in the Question Definition window. See image You can type the expression directly into this field, or use the Expression Builder which is a tool specially designed for creating Arezzo expressions.

The expression must point to the question whose value you want to use as the response to the question. For example, if you have a Date of Birth question on an eForm but you know that the data entry user will already have filled this in elsewhere you need to create an expression that points to the answered question. So if the original Date of Birth question appeared on the Cover eForm in the Screening visit, the expression in the derivation field for the new question would be screening:cover:dobirth

The above example is a simple derivation but they can become much more complex and can include a number of set terms, functions and operators. See the help topics for Arezzo for more information.

Different question types

When creating a derived question, the question type, unit, format and length must be relevant to the expected response. For example, if you wish to derive a date value, the derived question must be of a date/time type.

Deriving the value of a category question

When deriving the value of a category question rather than the code, the derivation expression must specify the text value rather than the code value.

Example 1

Suppose you have a category question called Fruit with codes/values:

a Apple

b Banana

c Cherry

d Damson

If you set a derivation expression to be:

Fruit

it will evaluate to one of the code values; a, b, c or d.

If you want the text value, the derivation must be:

case((Fruit = 'a', 'Apple'), (Fruit = 'b', 'Banana'), (Fruit = 'c', 'Cherry'), (Fruit = 'd', 'Damson'))

Example 2

Suppose you have a Gender question with codes/values

1 Female

2 Male

If you used the derivation expression:

'This patient is ' & gender

it will evaluate to the code value and the message would read "This patient is 1".

To achieve the correct message "This patient is Female", you would need to following derivation expression: