Capturing Subject Scales

By Tommy Jackson on November 1, 2015


Collecting data entered on a Visual Analog Scale (VAS) using paper is always subject to data measurement and entry errors. The challenge was to replicate the paper process electronically in order to eliminate post-data collection measurement and data entry errors. This would eliminate the need for multiple measures and duplicate data entry reducing errors and cost. This was especially important for this study as each data collection period consisted of 26 VAS and was repeated 5 times per subject throughout the study.

Adding to the challenge’s complexity was the necessary capability of the VAS line to be standardized to exactly 10 millimeters or expanded to fit across the screen of the data entry device. This complexity required logistics development to standardize the analysis and/or data capture of the information when different line sizes are used by different individuals and devices. In this case, the data collection location required the use of mobile device to collect the data. Further, if a subject received a certain combination of subscale scores during the pre-screening or follow up visits, the researcher was to receive an alert that the subject needed to be withdrawn from the study.

And finally, the Sponsor required the ability to monitor progress mid-study, including a table of results and a graph across time on a per-subject basis, as well as aggregated across sites.


Prelude Dynamics proposed to use Prelude EDC, an electronic data collection system, to accurately capture real-time study data and allow study participants to respond to questions using a VAS on a mobile device.

An administrative panel was proposed so that site-based researchers could provide access to appropriate set of scales.  The scales designation would be set up such that the VAS scale could be fixed or varied, depending on the researcher’s preferences or the visual ability of the study participant.

The proposal included tables and graphs designed to aggregate the data for mid-study review, including on a per-subject basis or across sites or study visits. Users could further refine mid-study reviews by selecting between complete scales or a single subscale. Utilizing Prelude EDC’s standard features available to all clients, the Sponsor could customize ad-hoc reports as well as search/filter the data to be analyzed in the tables, graphs and ad-hoc reports.


Using paper-based VAS creates a cumbersome post-data collection process because the responses have to be accurately measured and recorded. This generally requires a minimum two measurements, the comparison between them to ensure they fall within an acceptable error range, and the collection of an additional measure when they do not. Each measurement is an opportunity for error, and the process is time-consuming and costly. Nevertheless, VAS scales are popular because they provide an accurate scale and allow more variability to be measured between subject results. Instead of being confined to 10 data points, a maximum generally used in Likert scales, VAS allows for 100 data points to be measured when the standard 10 cm line is used and measures are taken every millimeter. Likert scales are also limited by the bias introduced through the labeling of each choice. VAS provides a greater degree of accuracy and are known to better detect clinically significant changes.


A solution to the issue is to allow subjects to enter information on an electronic VAS directly onto a mobile device using Prelude EDC, an electronic data capture system. Prelude provided the researchers with an administrative panel where they could enter basic subject information, assign a temporary password, and activate each survey. The researchers then instructed the subjects on how to change their password and use the system. As subjects entered the data directly on the mobile device, it became available for review on the administrative panel as well as for analysis via summaries (tables and graphs) and for use in ad-hoc reports.

Prelude EDC’s standard summaries, which assist in monitoring the data being collected on a per-subject, per-site or whole-study basis, were customized so that researchers could view tables and graphs across time on a per-subject basis, or a scale or subscale basis. Using Prelude EDC’s search and filter capacity allows these summaries to display data of only the cases fitting the search criteria. Additionally, certain users have permissions to create and export ad-hoc reports, which can be used to monitor additional criteria or to answer research questions. The data within the system is available for export 24/7/365, including the ability to export in multiple formats (e.g., SAS-ready format).

Results & Benefits

As subjects select a data point on the VAS, real-time data is entered into Prelude EDC. This eliminates the need for post-data collection measurement and data entry, reduces the opportunity for errors, and lowers cost to measure and duplicate data entry. Prelude EDC also prevents a subject from changing an entered answer, which ensures they answer in real-time and are not able to enter the information retrospectively or prospectively. Results are automatically calculated for the subscales. If a subject’s scores fall outside of the required threshold, site personnel receive immediate feedback that the subject does not qualify for the study.

Another Prelude EDC advanced feature is the Randomization module. When a subject is removed from the study, Prelude EDC’s Randomization module works behind the scenes to reassign the removed subject’s treatment code to a new subject. This ensures that sufficient cases were assigned for each treatment group to maintain the study’s viability. All collected data is accessible in real time for query, review, analysis and export.

About Prelude Dynamics & Prelude EDC

Prelude Dynamics is a global provider of customized web-based software systems for data collection, analysis and management of clinical trials, studies and registries. We streamline eClinical operations through our unique and innovative Prelude EDC software system, which allows us to rapidly configure data collection solutions for pharmaceutical, CRO, medical device, animal health, and university organizations.

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