Common Calculations

Using Expressions to Calculate Values in Ripple

Ripple allows you to automate calculations using Single Input questions with default expressions or Expression (read-only) type questions. This feature helps streamline data entry, logic-based responses, and standardized calculations for custom variables.

How to Create a BMI Calculator in Ripple (Pounds & Inches)

Creating a BMI calculator within Ripple ensures consistent BMI calculations and eliminates the need for respondents to use external tools. Follow the steps below to build an automated BMI calculation system within your survey.

Set Up a BMI Calculator

1. Create a BMI Calculator Panel

• Add a "Panel" question to group related inputs.
• Name it "BMI Calculator" to keep all BMI-related fields organized.

2. Add Weight Input Field

• Create a "Single Input" question type for Weight (pounds).
• Open the Properties Panel on the right.
• Under General Settings, enter "weight" in the Name field.

3. Add Height Input Fields

• Create a "Single Input" question type for Height (feet).
  • In the Properties Panel, set the Name field to "height_feet".
• Create another "Single Input" question type for Height (inches).
  • In the Properties Panel, set the Name field to "height_inches".

4. Add the BMI Calculation (Read-Only Expression)

• Create an "Expression (Read-Only)" question named "BMI".
• Open the Properties Panel on the right.
• Under General Settings, locate the "Expression" field and enter the following formula:

 120.0254120.0254

• In the "Display Style" dropdown, change the format to "Decimal" to ensure accurate BMI output.

5. Save the Survey

How This Works

📌 Weight is converted from pounds to kilograms using 0.453592.
📌 Height is converted from feet and inches to meters using 0.0254.
📌 The BMI formula is applied to compute the Body Mass Index.

How to Automatically Calculate a Respondent’s Age in Ripple

Calculating a respondent’s current age based on their date of birth (DOB) ensures accurate data collection and enables logic-based automation in surveys. This calculated age can also be linked to the participant profile card for easy reference.

Setting Up an Age Calculator

1. Create a Date of Birth Input Field

• Add a "Single Input" question to capture the respondent’s date of birth.
• Open the Properties Panel on the right.
• Under the General Section, enter "Birthday" in the Name field.
• In the "Input Type" dropdown, select "Date".

2. Create the Age Calculation Field

• Add an "Expression (Read-Only)" question.
• Open the Properties Panel on the right.
• In the "Expression" field, enter the following formula:

 age

• This function automatically calculates the respondent’s age based on their DOB.

3. Save the Survey

Click "Save Survey" to finalize the setup.

How This Works

📌 The Birthday field captures the participant’s date of birth.
📌 The Expression (Read-Only) field automatically calculates current age based on today’s date.
📌 The calculated age can be used for survey logic and stored on the participant profile card.

How to Automatically Capture Today’s Date in a Survey

Automatically recording today’s date in a survey can be useful for:
✔ Tracking consent signing dates
✔ Recording survey completion dates
✔ Automating follow-up emails or next steps

Capturing Today’s Date

1. Add a Date Field to Your Survey

• Open the Toolbox and add a "Single Input" question to your survey.

2. Configure the Date Field

• Open the Properties Panel on the right.
• Under the General dropdown, change the Input Type (green) to “Date”

3. Set the Default Value to Today’s Date

• Scroll to the Logic section in the Properties Panel.
• In the Default Value Expression field(red), enter:

 today

• This will automatically populate today’s date when the survey is opened.

4. Save the Survey

• Click "Save Survey" to apply the changes.

How This Works

📌 When a participant opens the survey, the date field automatically fills with today’s date.
📌 If the form is saved, the date remains fixed (it does not update when viewed later).
📌 Useful for time stamping consent forms and survey completions.

Important Warning About Using Expression (Read-Only) for Age Calculation

When using an Expression (Read-Only) type question to calculate age based on today’s date, the result is dynamic and will change over time.

How This Affects Age Calculations

📌 If a participant submits a survey on 8/15/2022, the today() function will calculate their age as of 8/15/2022.
📌 If you view the same survey later on 9/8/2022, the today() function will update to 9/8/2022, causing the age value to change.