Adding logic to your forms can help make them “smart” by improving the user experience, promoting cleaner data, and automating calculations.
Form logic includes:

• calculations
• cross-form logic
• skip logic
• constraints

When writing expressions for form logic it is necessary to use the correct syntax, including punctuation and spaces. Form logic is not case-sensitive.

### Referencing Items

There are two ways to reference an item on your form within a logic expression. Values can either be an item reference (e.g. age) or the literal value of an item (e.g. yes or 1).

SyntaxDescriptionExample
.References the current item’s value.The expression .>= and .<=65 in an age field's constraint settings would verify that the value (age) entered is between 18 and 65.
\${itemname}References the value of another item where itemname is the name of that item.The expression \${sex} = 'female' could be used in a skip logic setting on a pregnancy question to display the question only if the participant is female.

To use values from other forms see below.

### Conditions

Note: You can use either single quotes or double quotes, but single quotes are generally preferred for clarity. You would use double quotes if the string already contained a single quote. If you want this condition to work with multiple choices, use the formula twice with and / or.

DescriptionSyntax
Numeric Value\${itemname} = value
String Value\${itemname} = 'value'
\${itemname} = "value"
Null Value [Empty String]\${itemname} = ''
Multiple Select Numeric Value(s)selected(\${itemname}, choicename)
Multiple Select Character Value(s)selected(\${itemname}, 'choicename')

### Operators & Boolean Logic

DescriptionSyntax
Subtraction-
Multiplication*
Divisiondiv
Modulus (remainder)mod
Equal=
Not Equal!=
Less Than<
Less Than or Equal to<=
Greater Than>
Greater Than or Equal to>=
Manipulating the order of operations( )
All must be trueand
Any can be trueor

Boolean operators (and & or) return a value of either True or False. If you have a sequence of statements, all linked together with and, then to have a value of True every statement must be true; if even one is not true, then the whole expression’s value is False. With or, the threshold is much lower: only one of the statements needs to be true to evaluate to True (though any number can be true, as long as at least one is).

Parentheses control the order of operations of a statement and are often used even when not needed to clarify and to increase the readability of the code (e.g.(\${enddate}-\${startdate}) * 2). Lastly, modulus (mod) divides one number into another and returns the remainder. This has many uses well beyond the EDC realm, but one of the simplest examples is that many programs use it to tell when a number is even or odd (if mod 2 is 0 it’s even, 1 it’s odd), or to know if a number is equal to, or a multiple of, another number (in this case if mod-ing by say 7, any value that results in 0 would be a multiple of 7).

### Calculations

Enter the formula from the syntax column in the Calculation field (Form Designer) or the Calculate column (Form Template). Replace the items in brackets with the names of your own items.

CalculatesKeySyntax
BMI (adjusting for Metric or Imperial, and rounding to 2 decimal digits)weight = weight in lbs or kgs

height = height in cm or in

wh_units = weight and height units (1 for cm and kgs, 2 for in and lbs)
round(if(\${wh_units} = 2 and \${weight} != '' and \${height} != '', 703 * \${weight} div(pow(\${height}, 2)), if(\${wh_units} = 1 and \${weight} != '' and \${height} != '', 10000 * \${weight} div(pow(\${height}, 2)), 0)), 2)

Alternatively: round(if(\${weight} != '' and \${height} != '', if(\${wh_units} = 1, 10000 * \${weight} div(pow(\${height}, 2)), 703 * \${weight} div(pow(\${height}, 2))), 0))
Mean Arterial Blood Pressure (MAP)systolic = systolic blood pressure

diastolic = systolic blood pressure
(systolic + (2 * diastolic)) div 3

### Required

Enter the formula from the syntax column in the field that appears when you select Conditional in the Required field (Form Designer) or the Required column (Form Template). Replace the items in brackets with the names of your own items. Required conditions are only evaluated for items that are currently null (for example, no value has been entered).

DescriptionSyntax
Cancer Type shows if {cancerdiagnosis} is yes.\${cancerdiagnosis} = yes

### Skip Logic/Relevant

Enter the formula from the syntax column in the field that appears when you select Skip Logic and click the \${} Manually enter your skip logic in XLSForm Code button (Form Designer) or the Relevant column (Form Template). Replace the items in brackets with the names of your own items.

Skip Logic/RelvantSyntax
Does Participant Smoke?\${smoke} = yes

Relevant logic is ignored if the default column is populated for an item in a form. If an item has a default value, it populates when the form is opened or when a repeat is added regardless of whether the item is relevant or not. To avoid default values displaying before an item becomes relevant, use triggered calculations so the values don’t populate until the item becomes relevant, or use an if() statement. To use an if() statement in this case, use a default that has an if() statement that sets the value to null if the relevant condition is not met and sets it to the desired default if the relevant condition is met.

### Validation Criteria/Constraint

Enter the formula from the syntax column in the Constraint field (Form Designer) or the Constraint column (Form Template). Replace the items in the syntax column in brackets with the names of your own items. Constraint conditions are only evaluated for items that are currently non-null (for example, a value has been entered).

Validation Criteria/ConstraintSyntax
No Future Dates.<=today() [Please refer to https://docs.getodk.org/form-logic/#when-expressions-are-evaluated for an important caveat]
Age Must be Between 1 and 100 [Non-inclusive]\${age} > 1 and \${age} < 100
Must be in 24-Hour Format (HH:MM)regex(., '^(([0-1]{0,1}[0-9])|([2][0-3])):([0-5][0-9])\$')

### Hard Edit Checks (Form Template)

Hard edit checks are exclusive to the Form Template and can be used to enforce stricter standards on data entry than soft edit checks. Because they can make data entry more difficult for users, it is recommended that they be used only when the benefits to data quality outweigh the difficulties for the study personnel.

All checks that are not explicitly defined as hard edit checks are soft edit checks in all forms. The exception to this rule are forms used in the Participate module in which case all edit checks are automatically hard edit checks.

When a value is entered and it violates a hard check on an item, the value is rejected before it is stored, and the user will see a pop-up message. If the value entered causes a hard edit check to be violated on a different item (such as one already entered and saved that passed the validation criteria at the time) then the user will see an error message displayed on the item with the violated hard check, and it will have an orange background (distinct from the soft red background used for soft check error messages).

A user cannot navigate forward in the form or mark the form complete while a hard check error message is present. The user can add a manual or automatic query to a hard check item to close the form. However, the query will not hide the hard check error message.

Important: Special care must be taken when using relevant logic (hide/show) for an item with a hard required check. Once an item has a value, a required hard check will not allow the item to be cleared. To avoid this, the item’s required logic must indicate that the item is required only when the item’s relevant logic is met. If this is not implemented properly, the user may get into a state where they cannot clear an item even though that is the only way to make the data consistent with the relevant logic.

For example, if the item (or the group it is in) has relevant logic \${yn_item} = 1, then the hard required logic must also include \${yn_item} = 1 to ensure that the form works as intended. That will enforce the hard required check when the item is relevant, but will not enforce the check when the item is not relevant.

### To Make a Hard Edit Check for a Required Item:

1. Click the survey tab in the Form Template spreadsheet.
3. Enter strict.

### To Make a Hard Edit Check for a Constraint:

1. Click the survey tab in the Form Template spreadsheet.
3. Enter strict.

## Cross-Checks (Form Template)

### Referencing item values across forms and/or events

Reference the following examples when checking data across events, forms, repeating occurrences in a single event, or repeating occurrences in separate events. There are also examples of how to check specific values captured when a user adds a new participant.

### The following steps apply all of the examples below, unless otherwise stated:

1. Create an item with a type of calculate.
2. In the bind::oc:external cell, for that newly added calculate field, select clinicaldata from the drop-down list.
3. In the calculation cell for the new calculate item, copy and paste the appropriate sample text from the examples below, and replace the bold, italicized text with the OIDs (or object names) from your study.
4. Reference the new calculate field (as defined above) in any of the following cells to use the externally referenced value for display or in a logic expression:
• label
• hint
• calculation
• constraint
• required
• relevant
5. (Optional) To optimize performance, configure the crossform_references column on the survey sheet to include only the events that are needed for the cross-form logic on your form. Cross-form logic will work without this step, but the form will load more slowly. Simply enter a comma separated list of the Event OIDs used in your logic. Include current_event in the list if any logic on the form uses [@OpenClinica:Current=’Yes’].

For example, you would enter “SE_BASELINE,SE_VISIT2,current_event” if your form uses cross-form logic containing the events, “SE_BASELINE”, “SE_VISIT2”, and “[@OpenClinica:Current=’Yes’]”.

Notes:

• Even if your logic references an event by name instead of OID, you must include the Event OID in the list.
• If you use any of the examples that reference OIDs, the study must first be published in order to generate OIDs. You can publish the study to the test environment, then locate and reference the OIDs as needed (they do not change between the test & production environments), and include those OIDs in the calculation field as indicated below.
• You can reference object names instead of OIDs, but if the object name changes, you must update the calculation to include the updated object name. OIDs do not change for objects, so it is easier to maintain forms that include references to OIDs.
• You can create any single calculation by using a combination of OIDs and object names.

### Cross-check data against an item value in another event. Referencing the item value by item name

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following to the calculation cell, replacing the bold, italicized text with your specific object names:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@OpenClinica:EventName=’Event Name Here‘]/FormData[@OpenClinica:FormName=’Form Name Here‘]/ItemGroupData[@OpenClinica:ItemGroupName=’Item Group Name Here‘]/ItemData[@OpenClinica:ItemName=’Item Name Here‘]/@Value

### Cross-check data against an item value in another event. Referencing the item value by OID

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following to the calculation cell, replacing the bold, italicized text with your specific OIDs:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@StudyEventOID=’Event OID Here‘]/FormData[@FormOID=’Form OID Here‘]/ItemGroupData[@ItemGroupOID=’Item Group OID Here‘]/ItemData[@ItemOID=’Item OID Here‘]/@Value

### Cross-check data against an item value in a different form that is in the same event as this form

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following to the calculation cell, replacing the bold, italicized text with your specific OIDs:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@OpenClinica:Current=’Yes’]/FormData[@FormOID=’Form OID Here‘]/ItemGroupData[@ItemGroupOID=’Item Group OID Here‘]/ItemData[@ItemOID=’Item OID Here‘]/@Value

### Cross-check data against an item value in a specific repeat/row of a repeating group

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following to the calculation cell, replacing the bold, italicized text with your specific OIDs:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@StudyEventOID=’Event OID Here‘]/FormData[@FormOID=’Form OID Here‘]/ItemGroupData[@ItemGroupOID=’Item Group OID Here‘][Repeat Number Here]/ItemData[@ItemOID=’Item OID Here‘]/@Value

### Cross-check data against a value from a specific event occurrence in a repeating event

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following to the calculation cell, replacing the bold, italicized text with your specific OIDs:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@StudyEventOID=’Event OID Here‘][Event Repeat Number Here]/FormData[@FormOID=’Form OID Here‘]/ItemGroupData[@ItemGroupOID=’Item Group OID Here‘]/ItemData[@ItemOID=’Item OID Here‘]/@Value

### Cross-check data against the event start date for the current event

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following text to the calculation cell:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/StudyEventData[@OpenClinica:Current=’Yes’]/@OpenClinica:StartDate

### Cross-check data against the event start date in a different event

You can add a calculate item to your form to store the User Role or Username of the current user. You can then control which note items that user can see on a form by referencing that calculate item in the relevant cell for the note item.

For example, you may have a note item on your form that provides instructions to the CRA regarding what items must be verified for a form that only requires partial verification.

It is not necessary for any other user roles to see that note, so you can conditionally display the note to Monitors only.

To do this, follow the steps below:

1. Use the instructions below to Lookup User Role.
2. Include the note item with instructions for SDV.
3. In the relevant cell for the noteitem, reference the calculate item that now stores the current user’s role or username.

For example, \${currentrole}=”Monitor” (where currentrole is the name of the calculate item you created)

Note: Only the standard roles are available for reference. If you created a custom role of “Junior Monitor” based on the Monitor role, this only references the standard Monitor role. In the future, custom role names will be available for reference as well.

### Lookup User Role

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following text to the calculation cell:

instance(‘clinicaldata’)/ODM/ClinicalData/UserInfo/@OpenClinica:UserRole

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:externalcell and add the following text to the calculation cell:

### Lookup Participant ID

Add a calculate item. Include ‘clinicaldata’ in the bind::oc:external cell and add the following text to the calculation cell:

instance(‘clinicaldata’)/ODM/ClinicalData/SubjectData/@OpenClinica:StudySubjectID