Confidence intervals of reference limits in small reference sample groups
Article first published online: 30 JUL 2013
© 2013 American Society for Veterinary Clinical Pathology
Veterinary Clinical Pathology
Volume 42, Issue 3, pages 395–398, September 2013
How to Cite
Braun, J.P., Concordet, D., Geffré, A., Bourges Abella, N. and Trumel, C. (2013), Confidence intervals of reference limits in small reference sample groups. Veterinary Clinical Pathology, 42: 395–398. doi: 10.1111/vcp.12065
- Issue published online: 13 SEP 2013
- Article first published online: 30 JUL 2013
- Group partitioning;
- healthy animals;
- reference intervals
Reference intervals are the most common tool used to interpret results of laboratory tests. However, in veterinary clinical pathology, the number of available reference individuals is often small.
The purpose of this study was to investigate the effects of small reference sample groups on the imprecision of the reference limits.
Gaussian and log-Gaussian distributions of 10 ≤ n ≤ 750 values were analyzed. Reference limits and 90% confidence interval of limits (90% CI) were calculated. Imprecision of limits was estimated by the ratio of the width of the 90% CI: width of the reference interval (WCI/WRI).
For Gaussian distributions, the WCI/WRI ratio cannot be expected to be lower than 0.2 when n < 55. In log-Gaussian distributions, the ratio greatly increases for the upper limit with skewness toward high values, whereas it moderately decreases for the lower limit.
Independent of the size of the reference sample group, it is very important to report the CIs of the reference limits, which can be very large for small reference sample groups. When the sample size is very small (n < 20), calculations maybe misleading and it is better to instead report all values.