What is the Build My Calculation Tool? This is a tutorial to help you build your REDCap calculation one step at a time. The framework of the calculation is provided, and you fill in the blanks. How many blanks, and what kind of information is needed will depend on the calculation you want to build. As you specify the different elements, you can see them being added to the calculation in real time at the bottom of the survey page.
Build My Calculation Tool Information This tutorial has five different functions to create calculations with. Certain functions can be combined to do multiple calculations. There are more functions available in REDCap under the FAQ section , but this tutorial only includes the most common functions and combinations of those functions.REDCap Administrator for assistance. How REDCap Calculations work: REDCap can automatically pull data from fields across your project, perform a function, and then display an output. Calculations must be formatted in a particular way, which this tutorial will help you with. work in real time can pull data from different instruments and events can only compute numbers and dates work in data entry forms and in surveys can only output numbers Click on any of the calculations below to learn more about how they work:
Date Difference Function This function is used to calculate the difference between two date or datetime fields. Some common examples include: To calculate a participant's age, to know the time lapse between two clinic visits, or to send surveys after a certain amount of time. Basically anytime you want to display a time difference. Specify two date variables and an output format to get the difference between them. At least one or both date or datetime fields must exist as variables in your project and be validated as date or datetime fields. If you don't have two date fields, you can use 'today' or a fixed date as the second date field. Yes. Using 'today' is a great way to calculate the difference between a date field and today's date, but 'today' can cause data quality issues , as any time you open and save a form using 'today' in a calculation, that calculation will automatically take today's date and update your calculation. Only use 'today' if it's necessary. datediff([date1],[date2],'d','mdy')
Round Function This function is used to round a number to a certain decimal point. Anytime you want to round a number. You can add this function to any calculation, including a date difference calculation, a mean function, or BMI calculation. All you need to do is specify how many decimal points you want your output to round to at the end of calculation. Yes. It is common to use the round function with a BMI calculation, an average, or rounding an age. round(([weight]/([height]*[height]))*703,2)
If/Then Statement Function An IF statement is a function used to create conditional logic and generate an output based on the logic you specify. In its simplest form, the IF function says:IF ( statement with condition, result if statement is true, result if statement is false ) sky=blue, day , night ) An IF statement is a comparison. Here you are defining what data the statement will pull to use in the comparison. In REDCap, you want the comparison to be done against a variable that exists in your project. Although you can use If/Then statements for more than calculations and can use them to compare strings of text please remember that calculations cannot read or compute text fields. The calculation output must always be a number.
Some common examples include: scoring tools that have variables that contain options like "prefer not to answer" that are coded with a raw value, for example "98", which would skew your calculation. It could also be used to give you a certain output (this output will always be a number) based on another calculation. Once your if statement is added as a calculated field, you will see the numerical output in red:
Can I create nested if statements?IF statements may be used inside other IF statements ("nested"). For example, if you wanted a calculation to eliminate a variable that has 2 raw values that would skew the score like 98 "Prefer not to answer and 99 "Unknown", you could do the following:
Sum Function This function is used to add up any variables in your project that return a number value. Some common examples include: adding up scores on a scale, adding up answers to a quiz, adding up data across events. The fields you want to include in the sum calculation must exist as variables in your project. You can sum up radio buttons, drop down menus, text fields validated as numbers, and other calculated fields. The calculation will add up the raw values assigned to the answer options. Yes, make sure your answer options are coded according to the meaning of the question and that the coding is consistent. This way when you go to add them up, the score is reflective of the data meaning. Yes and No. Checkboxes function differently and the raw value will always be either '1' (checked) or '0' (unchecked) as opposed to other fields, where you can specify the raw number value. This means you can sum the number of checkboxes that are marked as "checked" but you will not be allowed to sum a value that is assigned to a checkbox. This works too. However, if one or more of the variables is blank, then the function will fail and the output will be blank. The sum function will sum all of the values that are filled out, ignore any blank values, and give you an output. sum([value1],[value2], [value3])
Mean Function This function calculates the mean for any variables in your project (except text fields that are not validated to a numerical value and checkboxes). Anytime you want the mean score from multiple numerical fields. Returns the mean (i.e. average) value of a set of values provided in the format mean([num1],[num2],[num3],...). The fields you want to include in the mean calculation must exist as variables in your project. You can use radio buttons, drop down lists, text fields validated as numbers, and other calculated fields. The calculation will average the raw values assigned to the answer options. No. Do not include checkboxes in your mean equation, as checkboxes function differently and the raw value will always be either '1' (checked) or '0' (unchecked) as opposed to other fields, where you can specify the raw number value. mean([hemoglobin1],[hemoglobin2],[hemoglobin3]) To start building your calculation, click the 'Next Page' button below
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