What Research Shows and Why 10 cm Calibration Matters
A Visual Analog Scale, or VAS, is a method for measuring subjective experiences by asking respondents to indicate the position on a line that best represents how they feel.
VAS measures are used in many areas of research to assess sensations and perceptions that are difficult to express using numbers alone, including pain, pleasantness, fatigue, sleepiness, and breathlessness.
Traditionally, a paper VAS consists of a 10 cm line. Respondents place a mark on the line, and the distance from the left endpoint is measured with a ruler and recorded as a value from 0 to 100 mm.
Digital VAS tools now allow the same type of response to be collected on tablets and smartphones.
Can VAS measurements still be used in the same way when paper is replaced by a screen?
Paper and digital VAS measurements show good agreement
Several studies have compared paper-based and digital VAS measurements.
In 2002, Jamison and colleagues compared paper VAS ratings with an electronic VAS displayed on a handheld computer in 24 healthy adults. Participants rated pain-related verbal descriptors and sensory stimuli. The overall correlation between paper and electronic responses was high, at r = 0.91. Correlations for individual stimulus types ranged from r = 0.86 to 0.97.
Sindhu and colleagues evaluated the reliability, validity, and responsiveness of a digital VAS in 33 people with upper-extremity injuries. Test–retest reliability was r = 0.96, while correlations with paper VAS and other pain rating methods ranged from r = 0.84 to 0.97.
In 2020, Escalona-Marfil and colleagues compared a 10 cm paper VAS with an electronic VAS displayed on a tablet in 102 healthy adults. The intraclass correlation coefficient between the two methods was 0.86, indicating good reliability. The average difference between paper and electronic scores was also small.
A systematic review and meta-analysis by Jibb and colleagues examined electronic pain data collection more broadly. Across the studies included in the meta-analysis, the pooled correlation between electronic and conventional pain assessment methods was 0.92.
Together, these findings indicate that appropriately designed digital VAS tools can produce measurements that correspond well with paper VAS results.
A digital VAS does not have to be exactly 10 cm
A 10 cm line is standard for many paper VAS applications, but a digital VAS does not necessarily need to have the same physical length to show good agreement with paper.
Turnbull and colleagues compared a 10 cm paper VAS with a 13.5 cm electronic VAS in 109 participants aged 10 to 73 years. Reliability was good despite the difference in display length, with an ICC of 0.94 in adults and 0.80 in children and adolescents.
A review by Byrom and colleagues also found that the display lengths of electronic VAS tools evaluated in published studies ranged from 21 to 200 mm. Most of the included studies reported that electronic and paper administration were comparable.
These findings suggest that digital VAS measurements can perform well even when the physical length of the scale differs from the traditional 10 cm paper format.
Replacing paper with a tablet, or a pen with a finger or stylus, is not in itself a major obstacle to VAS measurement.
Why calibrate a digital VAS to 10 cm?
Although a digital VAS does not have to be exactly 10 cm, displaying it at a true physical length of 10 cm offers several methodological advantages.
Matching the physical length of a standard paper VAS reduces one difference between paper and digital administration.
This was examined directly in a study by Bird and colleagues.
The researchers compared a 100 mm paper VAS with an iPad VAS set to a physical length of 100.06 mm. The iPad was locked in landscape orientation, and the interface was designed to prevent rotation or scaling from changing the displayed length.
In 22 healthy older adults, paper and iPad measurements showed a strong relationship, with an R² of 0.904.
The researchers also compared the position measured manually on the screen with the value calculated automatically by the application. The agreement was extremely high, with an R² of 0.9998.
This study demonstrates that a digital VAS displayed at approximately the same physical length as a paper VAS can produce closely corresponding measurements while allowing the response position to be converted into a numerical value with high precision.
Paper VAS measurements are not completely free from variation
Paper VAS measurements are also affected by practical differences in how they are prepared and used.
The type of paper, printer, print scaling, line thickness, writing instrument, ruler, and person measuring the response may all vary.
For example, automatic print scaling may cause a line designed to be 10 cm long to be printed at a different physical length. A thick pen mark may also make it unclear which part of the mark should be measured.
Paper VAS studies remain valid because the scale and measurement procedure are standardized to an appropriate degree and applied consistently within the study.
The same principle applies to digital VAS measurement.
The key issue is not simply whether the response is made on paper or on a screen. What matters is that the displayed scale, response method, anchor labels, and recording procedure are appropriately designed and used consistently.
Digital collection can also reduce measurement errors
With a paper VAS, the researcher must measure the response position with a ruler and then enter the value into a spreadsheet or database.
This process may introduce several types of error:
- variation in ruler-based measurement
- inconsistent rounding
- transcription errors
- missed responses or multiple marks
- mismatches between forms and participant information
A digital VAS can convert the response position directly into a numerical value, eliminating manual ruler measurement and data entry.
The response can also be stored together with the participant ID, scale item, experimental condition, date and time, and trial information. This can substantially reduce the work required to collect, organize, and prepare VAS data for analysis.
Digitalization is therefore not only a change in the response medium.
It is also a way to preserve the familiar VAS response format while reducing manual processing and avoidable human error.
rVAS can be calibrated to a true physical length of 10 cm
rVAS allows the VAS displayed on an iPad to be calibrated to a true physical length of 10 cm.
This makes it possible to match the physical length of a standard 100 mm paper VAS and reduce one difference when moving from paper to digital administration.
Instead of simply stretching the scale to fit the available screen width, rVAS uses physical calibration so that the intended display length can be clearly defined for the study.
Participants can respond by drawing a mark on the line using a finger, Apple Pencil, or compatible stylus, preserving an interaction that is close to marking a paper VAS.
The response position is automatically converted into a VAS value and stored together with the corresponding condition, scale item, participant, and repetition data. Results from multiple sessions can then be exported together in XLSX format.
In this way, rVAS preserves the familiar task of indicating a position on a line while digitalizing measurement, numerical conversion, storage, organization, and export.
Consistency matters more than the medium
Whether a paper or digital VAS is used, measurement conditions should be defined and applied consistently throughout the study.
For digital VAS measurement, researchers should determine in advance:
- the device to be used
- screen orientation
- physical display length of the VAS
- anchor labels
- whether responses are made with a finger or stylus
- whether the current value is visible during responding
- the initial response state
- the numerical range and recording precision
- the application and version used
Keeping these conditions consistent helps ensure that participants and measurement sessions are assessed using the same procedure.
Summary
Multiple studies comparing paper and digital VAS methods have reported good correlations, reliability, and comparability between the two formats.
Digital VAS tools have also shown good results when their physical display length differed from the traditional 10 cm paper scale. A digital VAS therefore does not have to be exactly 10 cm to be useful.
However, calibrating the displayed VAS to a true physical length of 10 cm has practical advantages. It reduces one physical difference from the standard 100 mm paper VAS and makes the measurement conditions easier to define and reproduce.
rVAS allows participants to respond on a VAS calibrated to 10 cm by drawing directly on the scale. The application then automates measurement, numerical conversion, data storage, organization, and XLSX export.
The aim is to preserve the familiar response format of a paper VAS while making research data collection and management more efficient.
About the cited studies: The studies discussed in this article evaluated the specific electronic VAS tools used in each study. They did not directly test the equivalence of rVAS and paper VAS.
References
- Jamison RN, Gracely RH, Raymond SA, et al. “Comparative study of electronic vs. paper VAS ratings: a randomized, crossover trial using healthy volunteers.” Pain, 2002. https://doi.org/10.1016/S0304-3959(02)00178-1
- Sindhu BS, Shechtman O, Tuckey L. “Validity, reliability, and responsiveness of a digital version of the visual analog scale.” J Hand Ther, 2011. https://doi.org/10.1016/j.jht.2011.06.003
- Bird ML, Callisaya ML, Cannell J, et al. “Accuracy, validity, and reliability of an electronic visual analog scale for pain on a touch screen tablet in healthy older adults: a clinical trial.” Interact J Med Res, 2016. https://doi.org/10.2196/ijmr.4910
- Escalona-Marfil C, Coda A, Ruiz-Moreno J, Riu-Gispert LM, Gironès X. “Validation of an electronic visual analog scale mHealth tool for acute pain assessment: prospective cross-sectional study.” J Med Internet Res, 2020. https://doi.org/10.2196/13468
- Turnbull A, Sculley D, Escalona-Marfil C, et al. “Comparison of a mobile health electronic visual analog scale app with a traditional paper visual analog scale for pain evaluation: cross-sectional observational study.” J Med Internet Res, 2020. https://doi.org/10.2196/18284
- Jibb LA, Khan JS, Seth P, et al. “Electronic data capture versus conventional data collection methods in clinical pain studies: systematic review and meta-analysis.” J Med Internet Res, 2020. https://doi.org/10.2196/16480
- Byrom B, Elash CA, Eremenco S, et al. “Measurement comparability of electronic and paper administration of visual analogue scales: a review of published studies.” Ther Innov Regul Sci, 2022. https://doi.org/10.1007/s43441-022-00376-2
