Calculations and Branching Logic

By J Kevan Essmyer

Acknowledgements:J. Phil Miller (WUSM Biostatistics)

Paul Harris (Vanderbilt CTSA)Jack Baty (WUSM REDCap Admin)

Yu Tao (WUSM REDCap Admin)

Overview

• REDCap Overview

• Calculations• Branching Logic• Expanded Data Validation Types• Data Quality Module• External Links functionality• Data Search Tool

Development “Try it” and

Production “Study Data” Servers

• http://www.biostat.wustl.edu/redcap – REDCap User Request forms – REDCap Project Request forms (IRB #)– Sidedoor security certificate (External Access)

• Both servers are WUSM HIPAA compliant web-based data capture systems

• REDCap Policy: Study data should only be collected on the Production server

Project Creation Flow Chart

Create Project –Project Name, Longitudinal or Cross-Sectional/ Survey

Excel SpreadsheetOr

Online Form Designer

Data EntryForms

Add Users and

Set User Rights

Test

Forms

Move to Production Status and start Data Collection

Define Study Events

(Longitudinal)

add Schedule (optional)

Recent Changes

• Hardware– Improved Dedicated MySQL Database server

• Software (REDCap 4.8.x)– Data Query Module– New data validation types– Search Tool– External Links

File Server

Host Server

WEB Server

Uploaded Files

Installation Files

WEB Server

WU Campus

Sidedoor Server

https://redcapsurvey.wustl.edu...

REDCap Survey

Data Entry /Admin

Data Entry /Admin

MySQL Server

MySQL Slave Server

Data

Sync

Biostatistics Secure Domain

Authenticated Access

Public HTTPS Access

Calculations• Variable Referrence: [event_id][variable name]

– Event Id obtained from events grid

• Logic Statement: (if(expression),True Result,False Result)

• Simple– [weight]*10000/([height]*[height])

• Complex• Calculating the Mean of groups with null valid range includes zero

The following equation will calculate the Mean of a list of variables –

( (if(Math.abs([A])>0,[A],0)) +(if(Math.abs([B])>0,[B],0))+(if(Math.abs([C])>0,[C],0)) )/( (if(Math.abs([A])>0,1,if([A]=0,1,0))+if(Math.abs([B])>0,1,if([B]=0,1,0))+if(Math.abs([C])>0,1,if([C]=0,1,0)) )

Built in Functions

"y" years 1 year = 365.2425 days

"M" months 1 month = 30.44 days

"d" days

"h" hours

"m" minutes

"s" seconds

"ymd" Y-M-D (default)

"mdy" M-D-Y

"dmy" D-M-Y

Type of calculation Notes / examples

round(number,decimal places) Round

roundup(number,decimal places) Round Up

rounddown(number,decimal places) Round Down

sqrt(number) Square Root

(number)^(exponent) Exponents

abs(number) Absolute Value

min(number,number,...) Minimum

max(number,number,...) Maximum

mean(number,number,...) Mean

median(number,number,...) Median

sum(number,number,...) Sum

stdev(number,number,...) Standard Deviation

datediff([date1], [date2], "units", "dateformat", returnSignedValue)

datediff([dob],[date_enrolled],"d")

datediff([dob],"05-31-2007","h","mdy",true)

Units

Date Formats

DATEDIFF F(x)

Javascript Math Library• Math.abs(a) // the absolute value of a • Math.acos(a) // arc cosine of a • Math.asin(a) // arc sine of a • Math.atan(a) // arc tangent of a • Math.atan2(a,b) // arc tangent of a/b • Math.ceil(a) // integer closest to a and not less than a • Math.cos(a) // cosine of a • Math.exp(a) // exponent of a (Math.E to the power a) • Math.floor(a) // integer closest to a, not greater than a • Math.log(a) // log of a base e • Math.max(a,b) // the maximum of a and b • Math.min(a,b) // the minimum of a and b • Math.pow(a,b) // a to the power b • Math.random() // pseudorandom number 0 to 1 • Math.round(a) // integer closest to a • Math.sin(a) // sine of a • Math.sqrt(a) // square root of a • Math.tan(a) // tangent of a

http://www.javascripter.net/faq/mathfunc.htm

Pitfalls of Calculations• Changes made to equations after the start of data collection

– Correct new calculated value will display on page load– Each form must be individually submitted to re-apply calculation

• Calculations should be considered a tool not data.– Calculation should be reapplied during data analysis.

• Multiple calculations on a form.– Order of execution is determined by the alphabetical ordering of it’s

associated variable/field name.• Calculation 1 [weight_met] =[weight]*.45359237• Calculation 2 [BMI]=[weight_met]/([height]^2)

• !!!Calculation 2 will occur before calculation 1– Calculate BMI in one step (Best Solution)or– Rename variable to change order (only other option)

Branching Logic

• Exposes form question if logic expression is true

– [Event Id][Variable Name] = "0"

• Checkboxes Format– [Event Id][variablename(code)]

• To check the value of the checkboxes: • '1' = checked • '0' = unchecked

– [race(2)] = "1"

[sex] = "0" display question if sex = female; Female is coded as 0, Female

[sex] = "0" and [given_birth] = "1" display question if sex = female and given birth = yes; Yes is codesd as 1, Yes

([height] >= 170 or [weight] < 65) and [sex] = "1" display question if (height is greater than or equal to 170 OR weight is less than 65) AND sex = male; Male is coded as 1, Male

[last_name] <> "" display question if last name is not null (aka if last name field is empty)

Online Designer

Branching Logic

• Calculation with in branching logic– [kwdays] > (10+1)

• Prevent deletion of – With existing logic

• (other logic statements) or <>"“

– Stand alone• <>""

Branching logic warning about hiding existing data

Can be a dangerous situation and is best avoided.

Expanded Field Validation Types

Data Quality Module (data queries)

Results

Data Quality Module (data queries)

External Links

• Embed hyperlinks in the REDCap project menu.– Websites, Other REDCap Projects, web tools

Data Search Tool

“?!!?”

User Rights

Branching

Logic

Scheduling

API

Data Dictionary

Data

Validation

REDCap Lifelines

• Built-in tutorial videos• Built-in Frequently Asked Question (FAQ)

guide• Demonstration Databases (Some Online, more

to come)• WUSM Biostat REDCap Email Help Queue– [redcap@rt.biostat.wustl.edu]– Monitored by 4 to 5 Administrators

REDCap Email Support

redcap@rt.biostat.wustl.edu

REDCap Goals

• Easy to use• Metadata Driven • Adaptable Features• Data entry validation• Self service tool

Questions?