Upsala J Med Sci 95: 305-307, 1990 

Glossary of Terms 

Many of the terms are defined according to an earlier refer- 
ence (1) . 

Value of quantity 

value of a quantity. The expression of a quantity in terms 
of a number and an appropriate unit of measurement 
( 2 )  - 

a quantity (2). 
numerical value (of a quantity). The number in the value of 

true value of a quantity. Is the value which characterizes 
a quantity perfectly defined, in the conditions which 
exist when that quantity is considered (2). 

conventional true value (of a quantity). A value of a 
quantity which , for a given purpose, may be substi- 
tuted for the true value (2). 

Analytical Performance Characteristics 

imprecision of the measurement procedure (s). The inherent 
imprecision of the measurement procedure is estimated 
from replication studies. By analysis of variance 
techniques the within-run and the between-run compo- 
nents of variation may be estimated: s, and s, denote 
the corresponding standard deviations, and s, stands 
for the total standard deviation of the measurement 
procedure (1). 

bias. 

total 

The average systematic error of the measurement 
procedure, as estimated by a comparison of method, e. 
g. comparison of patient values between the test 
method and a definitive method or a reference method 
(1). Bias has obtained the meaning of the difference 
between the conventional true value and the expected 
value of the local laboratory. 

error (TE)(4) = absolute error of measurement (3). T E  
is the rrsumfr of the systematic error and a component 
of the random error. 

systematic shift (SE). A systematic shift is the systematic 
error that occurs in the measurement procedure. It 
is expressed direct in units or as a factor times the 
inherent imprecision of the measurement procedure 
(1). 

20- 908573 305 



increase in random error (RE). An increase in the inherent 
random error of the measuremnt procedure is expressed 
as a factor by which the inherent imprecision is 
multiplied to give the imprecision of the measurement 
procedure under the influence of an analytical dis- 
turbance (1). 

frequency of errors. Refers to the incidence rate of ana- 
lytical disturbances, which occur in addition to the 
inherent errors. It is here expressed in percent of 
runs having analytical disturbances (1). 

Analytical Quality Specifications 

allowable analytical error (AAE) = total allowable error 
(TE,) = Analytical Quality Goal. AAE is a 95 % limit 
of error, i. e. 19 out of 20 test results should have 
errors less than this amount. AAE is a 1.96.~ limit 
of error, thus a recommended allowable s must be 
multiplied by 1.96 to express the error specification 
in the form of AAE (1). 

critical systematic shift (SE,). A term in the equation: 
AAE = bias + SE,.s + (component of RE,) 

which must be small enough so that the numerical 
value of AAE is not exceeded. 

critical increase in random error (RE,). See above. 

laboratory quality specification = analytical quality spe- 
cification of the laboratory. This is the specifica- 
tion given by the laboratory to its customers. If not 
otherwise stated it means that 95 % of the results 
delivered should be located within the specification 
limits. 

Quality Specifications including both analytical and non- 
analytical components 

clinical needs. This term is preferred to the term medical 
needs. It generally includes analytical limits but 
may also include non-analytical characteristics as 
turnaround time. 

clinical quality specifications. This term includes compo- 
nents of variation as preanalytical and ana- 
lytical errors. It also assumes standardized treat- 
ment and care of the patient. 

306 



Non-analytical Quality Specifications 
Turnaround time ( t,,, ) 
Utilization of analyses (investigations) 
Result interpretation 
Supply of available analyses and other services 
Cost of analyses 

Laboratory Quality Management 
= good laboratory practice (GLP) 

Quality laboratory practices 
Quality control 
Quality assurance 

Internal quality assurance 
External quality assurance 

REFERENCES 

1. Westgard J 0, Groth T, de Verdier C-H. Principles for 
developing improved quality control procedures. In: de Verdier 
C-H, Aronsson T, Nyberg A, eds. Quality control in clinical 
chemistry - Efforts to find an efficient strategy. Scand J 
Clin Lab Invest 1984;44 Suppl 172: 19-41. 

2. Zender R.Measurements in biological systems. Metrological 
principles and terminology. In: Kallner A ,  Bangham D, Moss D, 
eds. Improvment of comparability and compatibility of labora- 
tory assay results in life sciences. IFCC Master Discussion, 
1. Bergmeyer Conference 1988. Scand J Clin Lab Invest 1989;49 
Suppl 193: 3-10. 

3. Dybkaer R, Martin D V, Rowan R M eds. Good Practice in 
decentralized analytical clinical measurement. Scand J Clin 
Lab invest 1991;51 Suppl. In press. 

4. Westgard, J. O., Barry, P. L .  Cost-Effective Quality Control: 
Managing the Quality and Productivity of Analytical Processes. 
p. 1-231. AACC Press. Washington, DC 1986. 

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