Question type - Equation

From LimeSurvey Manual

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Short description

 Hint: Unlike all other question types, if an equation is hidden, it is still computed, its value being stored in the database.

 Hint: Equation question type allow to assign a value to another Question. See how to use assignment Operator.

Important.png  No HTML tag can be saved in the database due to security concerns.

This question type lets the author create an equation (e.g., a calculation or tailored report) and save it in a database variable. Equations can use any syntax supported by ExpressionScript. If you are handling numeric values make sure that you use the advanced question setting "Numbers only" as explained below.

You may find below an example on how to use this question type:

Equation q ex 01.png

Equation q ex 02.png


Editing an equation

Using dedicated setting

The best way to edit equation is to use dedicated setting : this allow using same equation for different languages, and to be sure than no HTML is integrated in equation. This allow you to show a complete sentence to user but save only the needed value in database : for example put {weightkg/tall} in equation setting and show “Your BMI is {self.NAOK}”.

If you need Expression inside : you have to add the curly brace.

Using Question text

You can do edits via the HTML/WYSIWYG editor or from the HTML source:

  • Using the WYSIWYG editor:


  • From the HTML source:


The edits in the source code are recommended when you wish to record in your response table a clean text or a clean numeric value. By editing the source, you can remove/delete any HTML code that can affect the storing process.


Help.png Hint: To check different HTML editors, please see the wiki section on the HTML editor mode.

General options



This option allows the survey administrators to request their respondents to answer certain survey questions. If the mandatory questions are not answered, the respondents will not be able to proceed further. If you have a question with multiple subquestions, and you require only certain subquestions to be answered, use the minimum answer attribute located under the Logic tab.

Help.pngIf you use any of the preinstalled themes and the mandatory question attribute is enabled, a red asterisk will be shown next to the question. If you wish to hide it, please check these instructions.

Available options

  • On - Question must be answered before the participant can proceed to the next page - the answer option 'No answer' is never shown.
  • Soft - If the question is not answered, a warning is shown when trying to proceed to the next page - however, the participant can choose to ignore the warning and proceed. Note that the 'No answer' option is still shown (if activated in survey presentation settings)
  • Off (default) - Question can be left unanswered

Condition (previously "Relevance equation")


If the result value of the condition is "1" or "true", the question is "relevant" in the survey context, i.e. it is shown to the survey participant. If not, the question is hidden. Any survey question allows you to specify a relevance equation. This function is the successor of conditions and supports much more complex conditional logic.

Syntax Highlighting

Whenever you save the condition, it is evaluated and syntax-highlighted. Any errors will be color coded so that you can quickly detect and fix them.

 Hint: To check if all conditions are used correctly within your survey, read about our show logic file feature.

Valid values

  • Any condition that makes use of the ExpressionScript syntax, without surrounding curly braces.


Here are good examples of syntax highlighting.


Always hide this question (hidden)


If enabled, the question will always be hidden - it will not be displayed to the survey participants. This function can be used in the following scenarios:

  • If you wish to prefill a question with a URL and you want not to have it displayed on the screen. This overrides any conditions used within the survey because the respective question will not even be embedded on the page.
  • If you wish to store or calculate a value on the fly via the ExpressionScript - Presentation.
Help.png Note: A common question type that is used with this function is the Equation one.

Available options

  • On
  • Off (default)

CSS class (css_class)


If you want to add special CSS classes to certain questions, you can enter the CSS class name(s) in this box. Make sure you leave an empty space between different class names.

Valid values

  • Any text string with a space between different CSS class names.
 Hint: You can also insert an expression in this box (New in 3.0.0 ). Remember that the output of the expression will not be updated dynamically.

Important.png  According to the W3C, CSS class names can contain only the characters [a-zA-Z, and 0-9] and ISO 10646 characters U+00A1 and higher, plus the hyphen (-) and the underscore (_). They cannot start with a digit, or a hyphen followed by a digit. LimeSurvey encodes CSS classes, but it does not fix it totally.

Relevance help for printable survey (printable_survey_relevance_help)


If you wish to print a survey, you can also print the relevance equations for each question. But, if you wish to offer instead an explanation rather than the expression on the printed form, fill in this box with the text explanation for the relevance equation.

Valid values

  • Any text and/or numbers you wish to be displayed on the printable form.


Equation (equation)


The result of the expression you type here will be stored in the response table and NOT the result(s) of the expressions typed in the question textbox. For example, you may want to display several expressions in the question textbox to display the respondents some statistics about herself. However, if you wish to store something different at the same time, then type the desired expression in this field.

This equation is used for all language.

Valid values


Insert page break in printable view (page_break)


This attribute is only active when you actually print a survey from the Printable View. It forces a page break before the question.

Available options

  • On
  • Off (default)

SPSS export scale type (scale_export)


This is used for SPSS export only. This attribute overrides the default scale guessed by SPSS. To learn what the different measurement scales do, please read the related SPSS documentation.

Available options

  • Default (default)
  • Nominal
  • Ordinal
  • Scale

Numbers only (numbers_only)


If you enable this option, the participant can only enter numbers in the text box(es).

For the equation question types, this setting indicates that the result could only be a number, not a string. This will guarantee proper calculations/conversions in follow-up equations regarding the decimal mark.

Behavior by question type

  1. Default: If the subject enters a value that is not a number, that value is immediately cleared from the text box so that the subject can enter an appropriate value.
  2. Array (Texts): If the numbers only option is disabled, the "Show totals for" and "Show grand total" options will be overruled, while the total text boxes will not be displayed.
  3. Equation: Enabling this option will force the equation results to be converted to a numeric value. If the equation result is not a number (and not blank), the equation will return NaN, being saved as an empty string in the response table.

Available options

  • On
  • Off (default)


Show in public statistics (public_statistics)


This attribute allows the survey administrator to chose if a particular question results should be displayed to the survey participants after they submitted the survey.

Help.png Note: To have the statistics displayed on the last page, do not forget to enable this functionality from the presentation & navigation settings. Otherwise, no statistics link will be displayed at the end of your survey.

The default setting for each question is 'Off' (=Do not show the question statistics to the respondents). You have to enable this for every single question if you want to show the survey statistics of that (those) particular question(s) to the survey participants after the survey submission.

Available options

  • On
  • Off (default)

Display chart (display_chart)


This attribute allows the survey administrator to choose if a chart that contains the question results should be displayed to the survey participants after they filled out the survey.

Help.png Note: To have the chart displayed on the last page, you have to enable the following options:

Available options

  • On
  • Off (default)

Chart type (chart_type)


This attribute allows the survey administrator to choose which type of chart will be displayed to the respondent once he/she finished filling out the survey.

Help.png Note: Do not forget to change the question and survey settings in order to have the charts displayed at the end on the survey. For more details, check the wiki section on the display chart question attribute.

Available options

  • Bar chart
  • Pie chart
  • Radar
  • Line
  • PolarArea
  • Doughnut