From LimeSurvey Manual
Revision as of 16:53, 26 June 2018 by Cdorin
- 1 Overview of Conditions in LimeSurvey
- 2 The conditions designer
- 3 Default condition combinations
- 4 Using ORed conditions between different questions: the use of scenario
- 5 Using the editor
- 5.1 Editor overview
- 5.2 Setting new conditions
- 5.3 Editing/Deleting conditions
- 5.4 Example: how to copy conditions
- 6 Things to watch out for
- 6.1 General considerations
- 6.2 Conditions using the 'no answer' predefined answer
- 6.3 Chained conditions
- 6.4 Limitations and workarounds
Overview of Conditions in LimeSurvey
LimeSurvey has a very powerful logical branching feature. It can be accessed by clicking on the Set conditions button - - located on each question bar.
In this chapter we will describe:
- what conditions you can find in LimeSurvey
- what you can and can't do with conditions
- what steps you need to learn to setup simple or more complex conditions
Hide/Show Branching Versus Jump Branching
You can design logical branching with LimeSurvey, which means that you can decide that some questions will be displayed only if some conditions are met like "Show question X if the answer to question Y was Z".
Our approach is to implement a Hide/Show Branching Logic:
- you can define a condition or a set of conditions on each question of your survey - if the condition is met, the question will be displayed:
- a question without a condition defined on it will always be displayed;
- a question with a condition defined on it will not be displayed unless the condition is met.
This approach is different from the Jump Branching Logic that is sometimes implemented by other softwares. In the Jump Branching Logic, the resulting action of a met condition would be to jump to another question (that is to say hide all questions in between). LimeSurvey doesn't implement this Jump Branching Logic method. Instead, if you wish to jump a series of questions, you should simply set the same condition on all the questions you do not wish to be displayed. For example, if the jump condition you want to set on Question2 is "Jump to Question5 if the answer to Question1 is 'Yes'", you can simply:
- set a condition on questions 2, 3 and 4 to only display "if the answer to Question1 was NOT 'Yes'"
LimeSurvey makes setting the same condition on multiple questions (and thus implementing Jump Branching Logic) easy by allowing you to "copy" a condition from one question to a series of others. In the above example, you would begin by setting the condition on Question2, then from the same screen you would copy that condition to Question3 and Question4.
Supported Types of Conditions
Basically, a condition can compare values, returning either true or false.
The values that can be compared are answers to previous questions. For instance, if you answer 'Yes' to Question1, Question2 will then be showed to the survey respondent:
At this point, it is important to understand what is considered an eligible question-entry for the condition editor:
A question-entry is either:
- a simple question (for all question types apart from Array questions)
- for instance: text questions, radio or dropdown lists, and even multiple choices questions
- or a row in Array questions (except for Array dual scale and Array multiple flexible questions)
- for instance: array with 5 radio buttons or array with label questions
- or either the left part or the right part of an Array dual scale question
- or each cell of an Array flexible question
As a matter of simplification, question-entries are just called "Question" in this document and in the condition editor.
- constant values
- for instance: "If you answered more than 18 years to the question below"
- Participants' profile data: To use data from the survey participants table, "Anonymized responses" must be set to NO. This option can be found in survey participant settings panel.
Several comparison operators are supported - from the simple "equals" to the advanced "regular expression":
- The basic ones refer to the "equal" and "not equal to" operations
- The greater/less than operator family is also available, and is usually useful when using numeric question-entries
- Please note that comparisons on numeric fields make use of the numeric order. For instance, 2 < 10
- If you're using a question entry whose type is text, the condition could be evaluated as "2" > "10" (string order)!
- Numeric questions, as well as text questions (when they have the 'numbers_only' attribute set), will use the numeric order for comparisons
- An advanced comparison operator using regular expressions is also available.
- The "Regular Expression" operator (don't panic! If you don't know what this means, then you don't need it)
- the pattern is not to be enclosed in '/' characters
- for instance: [a-zA-Z]$
How can I combine conditions?
You can build complex conditions by combining simple conditions with the AND and OR logical operators.
However, it is important to understand that LimeSurvey automatically determines which logical operator to apply. This means that the use of the OR or AND operators is determined according to the context of the condition.
We'll talk about complex conditions later. Let's first focus together on the elementary ones.
The conditions designer
First, you need to access the conditions designer. To do that, click on the question you wish to apply the condition to:
Now, look for the Set conditions button located on the top question bar:
Once accessed, the following page will be displayed:
The conditions designer panel can be divided into three sections:
The conditions designer toolbar
You may find on the toolbar the following options:
- Show conditions for this question: Click on this button to get a quick overview of the current existent conditions that are applied to your question.
- Add and edit conditions: It represents the default page that opens automatically once you click the Set conditions button. It is divided in two parts: (1) a table displaying all the existent conditions and (2) the add/edit conditions menu.
- Copy conditions: Sometimes, you wish to apply the same condition to X questions in order to get the Y question displayed at the end. For this, click on the Copy conditions. A new window will open displaying the current existent conditions added to your question (let's call it question3). To add them to question5, check the desired conditions you wish to be copied, select question5, and click on the Copy conditions button located on the bottom left part of the panel. For a short example, please continue reading the following wiki section.
- 'Save and close: Once you are done with the changes, click "Save and close to get your conditions saved.
- Move to question: In order not to leave the conditions designer panel while moving to another question, use the following option to select from the dropdown list the next question you wish to apply conditions to. Please note that the dropdown list displays the questions that are displayed in the survey before and after the current question.
- Close: If you wish to exit the panel without performing any changes, you can either go straight to the settings/structure tab and select the desired option or click Close, which is located in the upper right of the screen.
Overview of the existent conditions
This section displays all the existent scenarios and conditions, and the quick" version of the add/edit conditions menu.
The table allows you to either delete or edit a specific condition:
Please note that a Quick-add conditions and Delete all conditions button can be located in the upper right part of the table. While the first one fastens the process of adding conditions (read below to learn about all the options), the second allows you to delete via one click all the current existent conditions applied to your question.
The bottom part of the screen is allocated to the Add/edit conditions menu:
To understand how the conditions feature works in LimeSurvey, we will first present the elementary conditions.
Definition of elementary conditions
An elementary condition is simply a single condition without any OR or AND logical operators.
It is composed by:
- a left operand: the tested value. You can choose the tested value type by selecting the appropriate tab in the condition editor. It can either be a previous question or a survey participant attribute.
- a comparison operator. Choose the comparison operator you want to apply from the dropdown list (less than, less than or equal to, equals, not equal to, greater than or equal to, greater than, regular expression).
- a right operand: the comparison value. You can choose the comparison value type by selecting the appropriate tab in the condition editor. When you create a condition, you can select as the comparison value - a predefined value (answer), a constant, a question, a survey participant attribute, or a regular expression.
Example of elementary conditions and how to create them
- Show Question 'AAMN' if "the answer to Question 'Gender' is the predefined answer 'Male'"
- tested value = answer to Question "Gender"
- comparison operator = equals
- comparison value = predefined answer code (the 'Male' answer in this case)
- Show Question 'Alcohol' if "the answer to Question 'Age' is greater or equal than the numerical value '18'"
- tested value = answer to Question 'Age'
- comparison operator = greater than
- comparison value = the constant value '18'
- Show Question 'Alcohol' if "the answer to Question 'BirthDate' is greater than 2000-01-01"
- tested value = answer to Question 'BirthDate'
- comparison operator = Less than or equal to
- comparison value = '2000-01-01' (the format in the constant field: 2000-01-01)
- Show Question 'Alcohol' if "the the 'DrinkingHistory' participant's attribute" matches the 'Yes' string.
- tested value= the 'DrinkingHistory' value taken from the survey participants table
- comparison operator = equals
- comparison value = the constant value 'Yes'
Default condition combinations
As said earlier, LimeSurvey automatically decides which logical operator (AND or OR) should be applied between conditions depending on the 'context'.
Note also that the order in which you define your elementary conditions is not relevant as LimeSurvey will automatically reorder them according to its own logic.
Let's study this in detail. Two rules should be always remembered:
- First rule: conditions having the same tested value are ORed together
- Second rule: conditions having different tested value are ANDed together
First rule: conditions having the same tested value are ORed together
When you have several conditions, they are ORed together if they share the same tested value. This is the case if the condition applies to several answers of one single question. For example, a condition was applied below to three answers belonging to the same question: "if answer to Question 'FavColour' equals 'green' OR answer to Question 'FavColour' equals 'red' OR answer to Question 'FavColour' equals 'blue'", then Question 'BirthDate' will be displayed to the survey respondent:
Second rule: conditions having different tested value are ANDed together
When you have several conditions, they are ANDed together if they don't share the same tested values. For example, you may see below the case for several conditions based on different previous questions: If answer to Question 'Alcohol' equals "Y" answer AND answer to Question 'Gender' equals "F", then Question 'Alcoholconsumption' will be displayed to the survey respondent:
The multiple options questions
The Multiple choice and Multiple choice with comments question types will be displayed in two flavors:
- a Group of checkboxes flavor which let you set conditions on all possible answers of the respective question;
- a set of Single checkbox entries which lets you set conditions on each checkbox individually.
The group of checkboxes flavour
Now, let's focus on an example to better understand the difference between the two flavours. Let's imagine that we wish to display the 'Pointchoice' Question only if the respondent checks at least one of the tested answers listed under the 'MultipleOrganizations' Question.
As mentioned above, the group of checkboxes flavor allows you to set conditions on all possible answers of the respective question. Therefore, only the options that refer to responsibilities are selected as comparison values below:
As we can observe, the conditions get ORed due to the Group of checkboxes flavour selected in the beginning.:
ANDing conditions in multiple choice questions
Now, let's focus on a similar example. However, we are looking this time only for the most active members to ask them further questions. To do this, we make use of the Single checkbox flavour which allows you to set conditions based on each checkbox individually.
In this example, question X will be displayed if A and B are checked:
Once done, you can observe that the two conditions are ANDed now.
This means that your question will not be displayed unless both tested values (the selected subquestions) are checked by the respondents.
Using ORed conditions between different questions: the use of scenario
Now, you may argue that sometimes you need to have ORed conditions even when they are set on different questions (that is to say on different tested values). This is why we got scenarios!
Definition of a scenario
A scenario is simply a manual grouping of conditions in which some conditions are evaluated independently of other conditions from other scenarios. The complex condition resulting in this association of several scenarios will be met if only one scenario is met. In other words, scenarios are logical grouping of conditions, respecting the above rules, and which are ORed together to build complex conditions.
Everything described above applies to the conditions located in every scenario. By default, all the new conditions are created inside the Default Scenario, which uses number '1' as its identifier. When you create new conditions, you can choose whether they are added to the default scenario or not. To change the scenario, just use another identifier.
Adding a question to another scenario
When you create (or edit) a condition, you can modify the scenario in which the condition is stored by simply clicking on the add scenario button:
As you can observe, the default scenario uses as identifier '1'. To add conditions to different scenarios, change the identifier by typing a different number in the box.
The number id of a scenario has no importance and different scenarios can have non-continuous ids.
Example: creating three scenarios
Using the editor
First you access the condition editor:
- open the condition menu by clicking on the conditions icon in the question button bar, when viewing a question.
The top part of the window always shows any conditions already set for this question:
In the example above question B is set to only display if:
- The answer to the question-entry FBI of previous question A is "1"
- EITHER the answer to the question-entry CIA of previous question A is "5"
- OR the answer to the question-entry CIA of previous question A is "3"
In Add/Edit mode File:Conditions add.png, some specific actions are possible on each line such as:
- edit condition
- delete all conditions , delete this condition , delete all conditions from this scenario
- edit scenario
Setting new conditions
First select the scenario
The number id of a scenario has no importance and different scenarios can have non-continuous ids.
Select the tested value
Click on the tab corresponding to the type of the tested value you want: it is either a previous question or a value taken from the profile of the participant (token attribute).
Note that in order to use the Token your survey must:
- not use anonymous answers
- use a token table and closed access
Then select the entry you want as tested value.
If you select a question-entry (from the 'Previous questions' tab) and if this question uses predefined answers then the corresponding predefined answers are displayed in the Predefined tab of the comparison value selection.
Select the comparison operator
Several comparison operators can be used:
- The basic ones are equality, and inequality
- The greater/less than operator family is also available, and is usually only useful when using numeric question-entries
- Please note that comparisons on numeric fields honor the numeric order: for instance 2 < 10
- If you're using a question entry whose type is text, then the condition could be evaluated as "2" > "10" (string order).
- Numeric questions, as well as text questions having the 'numbers_only' attribute set, will use the numeric order for comparisons
- An advanced comparison operator using regular expressions is also available. When selected, the answer input box will automatically switch to the advanced mode.
Selecting an comparison value
Select the tab that corresponds to the type of comparison value you need: it can be a predefined answers, a constant value, an answer from a previous question, a value from a token attribute, or a regular expression (reserved for the advanced regular expression operator).
Then select or type in the value you want to use.
Note that if you select a value in a tab, then change the tab and select another value in this other tab, the first option you selected is lost.
When using predefined answers, you can then select one or more predefined answers:
- the possible answers for that question
- Choose the answer that you want to use
- You can choose multiple answers in one go by using the CTRL/SHIFT button to select one or more answers
After that click on the "Add Condition" button.
Apart from adding new conditions, the Add/Edit can be used to
- edit conditions
- delete conditions
- edit scenario
By clicking on the edit icon on a condition line, the edit condition form at the bottom is automatically displayed with the current settings for this condition. Note that in this mode you can only select one predefined answer.
Click the update condition button to update this condition.
- delete a single condition by clicking on this icon
- delete all conditions within a scenario by clicking on this icon
- delete all conditions from this question by clicking on this icon
Example: how to copy conditions
As said above, scenario numbers have no impact in the way conditions are evaluated. However, modifying the scenario numbers are needed in order to:
- decide in which order the scenario are displayed when using the printable version of a survey
- merge conditions from 2 scenarios (in order to merge scenario 10 to scenario 1, just renumber scenario 10 with scenario id 1).
Things to watch out for
There are a few basic rules you should keep in mind before setting conditions on a question:
- Once a single condition has been set for a question, that question will not display unless that condition is met.
- Conditions can only be set based on questions that appear before the question on which the condition is set.
- If you change the order of questions in your survey after you create conditions LimeSurvey does not warn you if the changed order will break a condition. You should always leave the creation of conditions until you are satisifed with the order of questions and groups in your survey.
- You can modify conditions even after a survey has been activated. This should be done with caution, as there is no "consistency checking" applied here.
Conditions using the 'no answer' predefined answer
Setting the following condition "Show question Q20 if answer to question Q1 is 'no answer'" really means "show question Q20 if question Q1 was displayed and received no answer". This is not equivalent to "show question Q20 if question Q1 was not displayed"
If you set conditions on a question that, itself, has conditions, then there may arise occasions where the survey behaves in ways you might not have predicted. For example a typical side-effect is that if you hide all questions in a group with chained conditions that the group header will still be shown unless you correct these conditions as explained below.
In the example above a question is displayed 'Do you like being male?' which has conditions set, and which will only display if the answer to What is your gender? is M. If you were to add a condition to this question requiring a specific answer from the Do you like being male? question, then this question will never display, because the question Do you like being male will not be presented.
It is highly recommended that you copy the conditions from the earlier question to the one you're editting.
For instance, you want the following:
- Q1 is a Gender question
- Q2 is a Yes/No and is displayed if answer to Q1 is Male
- Q3 is a ranking question and is displayed if Q2 is Yes
What you really need to setup is the following set of conditions:
- on Q2: display question if answer to Q1 is Male
- on Q3: display question if answer to Q1 is Male AND answer to Q2 is Yes
After correction, the correct set of conditions for Q3 should look like:
So if you are designing a complicated survey with large number of conditions, make sure you test the survey for as many different combinations of results as you can think of.
Limitations and workarounds
If you create a survey where many questions get skipped because of conditions, the progress bar either jumps over a set of questions or the survey ends at 50%.
To avoid such behavior, the questions that could be skipped should be arranged between the shown questions. In this way only one or two questions get skipped per answer.
For example, based on question one (yes or no question) 14 questions will be asked question 2A to 15A when the answer of question one was yes, 2B to 15B when the answer to question one was no.
If you arrange the questions in one group and arrange them like: 2A, 2B, 3A, 3B, and so on you will get a nearly correct progress bar, while arranging the questions like 2A, 3A, 4A, [...], 2B, 3B, 4B, ... you will get a progress bar from 0 to 50% or from 50% to 100%, depending on the answer to the first question.
Setting a constant comparison value for a "Date" Question Type
You have to use the internal representation of Date values, which is YYYY-MM-DD to define your constant comparison value.
Setting conditions for "Other" Options in the Multiple Options Question Type
In the multiple options question type, you can use the "Other" provided in the question type as a valid choice but you cannot set conditions on it. For example: Question No 1 says "Which color do your prefer to use?" Answer checkbox choices are Blue, Black and Other. If the participant chooses Blue, you can set a condition. If the participant chooses Black, you can set a different condition. However, if the participant chooses "Other" and types in something in the text box, there is NO way a condition can be set. LimeSurvey does not recognize if the participant chose the "Other" condition. This is NOT a bug but a limitation.
There is no real field recorded for the 'other' checkbox for this question type. Thus, the only way to know if the user has answered the 'other' part of the question or not would be to check if the value of the text written in the other input field is empty or not.
However, due to the specific way we handle Multiple choice questions, testing the 'other' text input field has never been implemented.
As a workaround, add an explicit answer option called 'Other' and do not use the built-in 'other' option of these question types. Then add an additional short text question which will be displayed if this 'Other' checkbox was clicked.
How to use parenthesis for the boolean expressions?
If you want to design something like:
(condition1 OR condition2) AND (condition3 OR condition4)
you'll have to set up:
(condition1 AND condition3) OR
(condition1 AND condition4) OR
(condition2 AND condition3) OR
(condition2 AND condition4)