Within- and Among-Observer Variation in Measurements of Animal Biometrics and their Influence on Accurate Quantification of Common Biometric-Based Condition Indices

• Published in: Annales zoologici fennici 2010-10, Vol.47 (5), p.323-334
• Main Authors: Goodenough, Anne E, Stafford, Richard, Catlin-Groves, Christina L, Smith, Angela L, Hart, Adam G
• Format: Article
• Language: English
• Subjects: Animal wings; Animals; Biometrics; Bird songs; Birds; Body size; Error rates; Mathematical independent variables; Observational research; Tarsus
• ISSN: 0003-455X; 1797-2450
• DOI: 10.5735/086.047.0503

Research using biometric data relies on consistent measurements within, and often among, observers. However, research into the relative importance of intra- and inter-observer variability is limited. More importantly, the influence of biometric variability on accurate quantification of biometric-based condition indices has not been analysed: it is unclear whether multiple errors become magnified or cancel one another out. Here, we quantify intra- and inter-specific variability in multiple biometrics, and derived condition indices, using museum bird specimens. Inter-observer variability was higher than intra-observer variability for all parameters. Measurement error (ME) varied from < 1% to > 50% for different biometrics. ME was magnified in condition estimates, reaching > 80% within-observers and > 90% among-observers. Significant differences in mean measurements were found for 17% and 67% of biometrics within-and among-observers, respectively; for condition indices, the figures were 50% and 67%, respectively. We discuss the implications of these findings for research into species' ecology, taxonomy and behaviour.