Table 1: Conversions of five, seven, and eleven-point scales to 0–100 points (101-point scales) What If 0 Is in the Middle? Table 1 shows the conversion of five-, seven-, and eleven-point scales. For seven-point scales, subtract 1 from the responses and multiply by 16.6666667 (the desired maximum of 100 divided by the subtracted, unstretched maximum of 6). Using a method similar to the positive-tone items of the SUS, reset a five-point scale to start at 0 by subtracting 1 from the response options and then multiplying by 25 (the desired maximum of 100 divided by the subtracted, unstretched maximum of 4). It’s trickier when the original scale starts at 1. If the initial scale starts with 0, like the standard eleven-point likelihood-to-recommend item used to compute Net Promoter Scores, all you need to do is divide the rating by the highest possible value and multiply by 100. In short, there are some practical advantages to presenting attitudinal data on a 0–100-point scale where 0 is the worst possible outcome and 100 is the best. (Also, where differences in perceived usability were achieved, having a scale of 0 to 100 was likely to make the differences be perceived by team members as being greater than on a smaller scale-not that it makes any difference when it came to actual analysis.) Project managers, product managers, and engineers were more likely to understand a scale that went from 0 to 100 than one that went from 10 to 50, and the important thing was to be able to grab their attention in the short space of time they were likely to spend thinking about usability, without having to go into a detailed explanation. 35) recalled the rationale for making these adjustments:īut why is there the rigmarole around converting the scores to be between 0 and 4, then multiplying everything by 2.5? This was a marketing strategy within DEC, rather than anything scientific. In his 2013 retrospective on the SUS, Brooke (2013, p. To stretch it out from 0 to 100, multiply the sum by 2.5, which is the value you get after dividing the target maximum of 100 by the unadjusted maximum of 40.
A negative-tone rating of 5 becomes 0, and 1 becomes 4.Īdding the scores would produce a scale that would range from 0 to 40 in one-point increments. For example, a positive-tone rating of 5 becomes 4, and 1 becomes 0. This converts all raw ratings to a nonstandard five-point scale ranging from 0 (poorest rating) to 4 (best rating). For negative-tone items, subtract the item rating from 5. For positive-tone items, subtract 1 from the item rating. The standard SUS is made up of ten five-point mixed-tone items and produces scores that can range from 0 (worst) to 100 (best).īecause the tone of the items in the standard SUS is mixed-half positive (odd items) and half negative (even items)-the first step in scoring the SUS by hand is to convert all the items to the same scale. According to Google Scholar, the original SUS paper ( Brooke, 1996) has been cited over 9000 times, and that only accounts for its use in published research. How SUS Scoring Worksĭeveloped in the mid-1980s, the SUS is a popular measure of perceived usability for UX practitioners and researchers. Rating scales that have the same number of response options but have opposite interpretations of their numbers (e.g., for one scale 1 is worst and 5 is best, but for another 1 is best and 5 is worst)Īn alternative way to handle both reporting rating scale data and interpreting different point scales is by converting scores to fall on a scale from 0 to 100 (technically a 101-point scale), something done with the popular System Usability Scale (SUS).