Graphical interpretation of confidence curves in rankit plots
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Per Hyltoft Petersen
Abstract
A well-known transformation from the bell-shaped Gaussian (normal) curve to a straight line in the rankit plot is investigated, and a tool for evaluation of the distribution of reference groups is presented. It is based on the confidence intervals for percentiles of the calculated Gaussian distribution and the percentage of cumulative points exceeding these limits.
The process is to rank the reference values and plot the cumulative frequency points in a rankit plot with a logarithmic (ln=loge) transformed abscissa. If the distribution is close to ln-Gaussian the cumulative frequency points will fit to the straight line describing the calculated ln-Gaussian distribution. The quality of the fit is evaluated by adding confidence intervals (CI) to each point on the line and calculating the percentage of points outside the hyperbola-like CI-curves. The assumption was that the 95% confidence curves for percentiles would show 5% of points outside these limits. However, computer simulations disclosed that approximate 10% of the series would have 5% or more points outside the limits.
This is a conservative validation, which is more demanding than the Kolmogorov-Smirnov test. The graphical presentation, however, makes it easy to disclose deviations from ln-Gaussianity, and to make other interpretations of the distributions, e.g., comparison to non-Gaussian distributions in the same plot, where the cumulative frequency percentage can be read from the ordinate. A long list of examples of ln-Gaussian distributions of subgroups of reference values from healthy individuals is presented. In addition, distributions of values from well-defined diseased individuals may showup as ln-Gaussian.
It is evident from the examples that the rankit transformation and simple graphical evaluation for non-Gaussianity is a useful tool for the description of sub-groups.
Copyright © 2004 by Walter de Gruyter GmbH & Co. KG
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- Editors introduction
- Reference values: from philosophy to a tool for laboratory medicine
- The evolution of the reference value concept
- Normality: the unreachable star?
- Selecting clinically relevant populations for reference intervals
- The IFCC recommendation on estimation of reference intervals. The RefVal Program
- Graphical interpretation of confidence curves in rankit plots
- Partitioning biochemical reference data intosubgroups: comparison of existing methods
- Parametric methods for estimating covariate-dependent reference limits
- Reference regions of two or more dimensions
- Should we maintain the 95 percent reference intervals in the era of wellness testing? A concept paper
- Clinical interpretation of reference intervals and reference limits. A plea for assay harmonization
- Inherent biological variation and reference values
- Intraindividual reference values
- Guideline for the production of multicentre physiological reference values using the same measurement system. A proposal of the Catalan Association for Clinical Laboratory Sciences
- Proposal for guidelines to establish common biological reference intervals in large geographical areas for biochemical quantities measured frequently in serum and plasma
- Reference intervals for plasma proteins: similarities and differences between adult Caucasian and Asian Indian males in Yorkshire, UK
- Diagnostic and epidemiological implications of regional differences in serum concentrations of proteins observed in six Asian cities
- Study of reference values and biological variation: a necessity and a model for Preventive Medicine Centers
- Creation of a low-risk reference group and referenceinterval of fasting venous plasma glucose
- Establishment of a serum thyroid stimulating hormone (TSH) reference interval in healthy adults. The importance of environmental factors, including thyroid antibodies
- Difficulties in establishing reference intervals for special fluids: the example of 5-hydroxyindoleacetic acid and homovanillic acid in cerebrospinal fluids
- Metrological traceability of calibration in the estimation and use of common medical decision-making criteria
- Creation of the necessary analytical quality for generating and using reference intervals
- Analytical quality specifications for common reference intervals
- Design of internal quality control for reference value studies
- The NEXUS vision: an alternative to the reference value concept
- Meetings and Awards
Articles in the same Issue
- Editors introduction
- Reference values: from philosophy to a tool for laboratory medicine
- The evolution of the reference value concept
- Normality: the unreachable star?
- Selecting clinically relevant populations for reference intervals
- The IFCC recommendation on estimation of reference intervals. The RefVal Program
- Graphical interpretation of confidence curves in rankit plots
- Partitioning biochemical reference data intosubgroups: comparison of existing methods
- Parametric methods for estimating covariate-dependent reference limits
- Reference regions of two or more dimensions
- Should we maintain the 95 percent reference intervals in the era of wellness testing? A concept paper
- Clinical interpretation of reference intervals and reference limits. A plea for assay harmonization
- Inherent biological variation and reference values
- Intraindividual reference values
- Guideline for the production of multicentre physiological reference values using the same measurement system. A proposal of the Catalan Association for Clinical Laboratory Sciences
- Proposal for guidelines to establish common biological reference intervals in large geographical areas for biochemical quantities measured frequently in serum and plasma
- Reference intervals for plasma proteins: similarities and differences between adult Caucasian and Asian Indian males in Yorkshire, UK
- Diagnostic and epidemiological implications of regional differences in serum concentrations of proteins observed in six Asian cities
- Study of reference values and biological variation: a necessity and a model for Preventive Medicine Centers
- Creation of a low-risk reference group and referenceinterval of fasting venous plasma glucose
- Establishment of a serum thyroid stimulating hormone (TSH) reference interval in healthy adults. The importance of environmental factors, including thyroid antibodies
- Difficulties in establishing reference intervals for special fluids: the example of 5-hydroxyindoleacetic acid and homovanillic acid in cerebrospinal fluids
- Metrological traceability of calibration in the estimation and use of common medical decision-making criteria
- Creation of the necessary analytical quality for generating and using reference intervals
- Analytical quality specifications for common reference intervals
- Design of internal quality control for reference value studies
- The NEXUS vision: an alternative to the reference value concept
- Meetings and Awards
