Visual Analog Scales (VAS) are used because they provide greater accuracy and are more sensitive when measuring a variable that is on a continuum as compared to Likert scales. VAS scales are traditionally used to measure things such as pain and function. Researchers tend to prefer obtaining more accurate data, but have shied away from using VAS because measuring it accurately is time consuming and errors can be easily made. Measuring VAS on paper requires multiple people to measure the location of the mark, and photocopying could change the length of the line.

eVAS captures the same information as previously captured on paper. When the patient touches the screen or clicks on the line, a mark is recorded. The value of this mark is then automatically calculated by the system, eliminating the need of multiple measures and removing errors from the process. This makes eVAS more accurate and superior to Likert scales.

So what are we waiting for? The greatest concern is whether the line can be exactly 100 mm on every screen it is viewed on. Prelude Dynamics solves this issue by using one of two methods: either using a set length line that is not affected by the device’s screen size or by allowing users to calibrate their device using a 10 cm line, such as the length of a credit card. Either will ensure the length of the line.

Alternatively, does it really matter that the line is not exactly a certain length? The length was set when humans needed to be able to easily read the location of the mark on a line, so a scale of 100 mm was appropriate. With computers, the location can be calculated relative to the length of the line with accuracy to infinite decimal points on a by-pixel scale. According to an article in the International Journal of Medical Research, there is no significant difference between the two lengths they examined (100 mm and 75 mm) therefore they recommend the use of eVAS on iPads for patient clinical data collection.

Several studies have been conducted using VISION™’s eVAS. The users report it is easy to use and improves accuracy of the results. Learn more about one such study by reviewing the VAS case study. Consider adding eVAS to your next study if it makes sense for what you are researching.


Jim Pedzinski - VP of Business Development
jpedzinski[at] - 512-476-5100 ext. 210