The accuracy of fingerbreadth measurements using our own fingers and visual estimation

In clinical practice, fingerbreadth measurement is a common technique. However, there isn't a universally established standard for using fingerbreadth measurements. In this study, we examined the differences between measurements using visual estimation and measurements using one's own fingerbreadth. Additionally, we assessed their reliability as a clinical measurement tool. Twenty-five participants were tasked with estimating the length of rod pieces using visual estimation and their own fingerbreadths. The collected data were then analyzed in the following ways: 1. A comparison between visual estimation and one's own fingerbreadth measurements. 2. A concordance correlation analysis between the actual size and measurements taken through visual estimation or one's own fingerbreadth. 3. Bland–Altman analysis comparing the measurements from visual estimation and one's own fingerbreadth against the actual length of the corresponding rod piece. Additionally, the same comparisons were conducted with a 1-m distance between the participants and the rod pieces. Significant differences were observed between visual estimation and one's own fingerbreadth measurements for fingerbreadth-based measurements. For centimeter-based measurements, most comparisons did not show significant differences. The concordance correlation coefficient between visual estimation and actual lengths was below 0.9, indicating poor agreement. In contrast, the concordance correlation coefficient between fingerbreadth measurements and actual lengths was 0.9723, indicating substantial agreement. Visual estimation showed percentage errors exceeding the 30% agreement limit (41%), indicating poor interchangeability as a clinical ruler. For one's own fingerbreadth measurements, the percentage error was well below the 30% limit (16%), indicating good interchangeability. Supplementary analyses with data collected while maintaining a distance showed similar results. The concordance correlation coefficient for fingerbreadth measurements decreased to 0.9247, indicating moderate agreement, and percentage errors increased from 16% to 24% but stayed within the 30% agreement limit. There may indeed be significant differences between visual estimation and one's own fingerbreadth measurement. One's own fingerbreadth measurement can serve as a substitute for a clinical ruler, whereas visual estimation cannot. Finally, when measuring objects from a distance, it's important to remember that fingerbreadth measurement methods become less effective as a reliable ruler.