biostatistics Biostatistics (also known as biometry) are the development and application of statistical methods to a wide range of topics in biology. It encompasses the design of biological experiments, the collection and analysis of data from those experime ...

, spectrum bias refers to the phenomenon that the performance of a

diagnostic test A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, diagnostic imaging, genetic t ...

may vary in different clinical settings because each setting has a different mix of patients. Because the performance may be dependent on the mix of patients, performance at one clinic may not be predictive of performance at another clinic. These differences are interpreted as a kind of ''bias''. Mathematically, the spectrum bias is a

sampling bias In statistics, sampling bias is a bias (statistics), bias in which a sample is collected in such a way that some members of the intended statistical population, population have a lower or higher sampling probability than others. It results in a bia ...

and not a traditional

statistical bias Statistical bias is a systematic tendency which causes differences between results and facts. The bias exists in numbers of the process of data analysis, including the source of the data, the estimator chosen, and the ways the data was analyzed. ...

; this has led some authors to refer to the phenomenon as ''spectrum effects'', whilst others maintain it is a bias if the true performance of the test differs from that which is 'expected'. Usually the performance of a diagnostic test is measured in terms of its

sensitivity Sensitivity may refer to: Science and technology Natural sciences * Sensitivity (physiology), the ability of an organism or organ to respond to external stimuli ** Sensory processing sensitivity in humans * Sensitivity and specificity, statisti ...

and specificity and it is changes in these that are considered when referring to spectrum bias. However, other performance measures such as the likelihood ratios may also be affected by spectrum bias. Generally spectrum bias is considered to have three causes. The first is due to a change in the case-mix of those patients with the target disorder (disease) and this affects the

. The second is due to a change in the case-mix of those without the target disorder (disease-free) and this affects the specificity. The third is due to a change in the prevalence, and this affects both the

and specificity. This final cause is not widely appreciated, but there is mounting

empirical evidence Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences ...

Leeflang MM, Bossuyt PM, Irwig L., Diagnostic test accuracy may vary with prevalence: implications for evidence-based diagnosis, J Clin Epidemiol. 2009 Jan;62(1) 5–12. as well as theoretical arguments which suggest that it does indeed affect a test's performance. Examples where the

and specificity change between different sub-groups of patients may be found with the

carcinoembryonic antigen Carcinoembryonic antigen (CEA) describes a set of highly related glycoproteins involved in cell adhesion. CEA is normally produced in gastrointestinal tissue during fetal development, but the production stops before birth. Consequently, CEA is us ...

test and urinary dipstick tests. Diagnostic test performances reported by some studies may be artificially overestimated if it is a case-control design where a healthy population ('fittest of the fit') is compared with a population with advanced disease ('sickest of the sick'); that is two extreme populations are compared, rather than typical healthy and diseased populations.Rutjes AWS, Reitsma JB, Vandenbroucke JP, Glas AS, Bossuyt PMM, Case-control and two-gate designs in diagnostic accuracy studies, Clin Chem 2005;51(8):1335–41. If properly analyzed, recognition of

heterogeneity Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...

of subgroups can lead to insights about the test's performance in varying populations.

References

{{DEFAULTSORT:Spectrum Bias Biostatistics Bias Design of experiments Medical statistics

See also

References