Total serum bile acids were estimated by an enzymic (3alpha-hydroxysteroid dehydrogenase) method ... more Total serum bile acids were estimated by an enzymic (3alpha-hydroxysteroid dehydrogenase) method in 173 fasting patients with different liver diseases, classified into 17 groups by morphological criteria. The results were not highly correlated with those for any of the other 24 tests included in the study, but moderate correlations were observed with bilirubin or alanine aminotransferase (positive) and with prealbumin (negative) in a few patient groups. The sensitivity of total bile acids in serum of fasting individuals as a liver-function test was rather high, comparable with that of serum enzymes. When discriminant analysis was used to identify optimal combinations of tests for the separation of different groups of liver diseases, we found that data on serum bile acids added some new information to that carried by the other 24 tests.
We studied the potential benefit of using artificial neural networks (ANNs) for the diagnosis of ... more We studied the potential benefit of using artificial neural networks (ANNs) for the diagnosis of thyroid function. We examined two types of ANN architecture and assessed their robustness in the face of diagnostic noise. The thyroid function data we used had previously been studied by multivariate statistical methods and a variety of pattern-recognition techniques. The total data set comprised 392 cases that had been classified according to both thyroid function and 19 clinical categories. All cases had a complete set of results of six laboratory tests (total thyroxine, free thyroxine, triiodothyronine, triiodothyronine uptake test, thyrotropin, and thyroxine-binding globulin). This data set was divided into subsets used for training the networks and for testing their performance; the test subsets contained various proportions of cases with diagnostic noise to mimic real-life diagnostic situations. The networks studied were a multilayer perceptron trained by back-propagation, and a l...
The clinician often orders more tests than the test combination necessary for solving an actual c... more The clinician often orders more tests than the test combination necessary for solving an actual clinical problem, thus increasing costs and the complexity of interpretation. The identification of optimal combinations of laboratory tests for commonly encountered or difficult clinical problems is therefore highly desirable. The authors review their experiences using multivariate analysis to identify combinations of tests that distinguish clinical categories of liver disease and of thyroid function.
Scandinavian Journal of Clinical & Laboratory Investigation, 1978
A general-purpose statistical program package (BMDP) has been linked by a simple program interfac... more A general-purpose statistical program package (BMDP) has been linked by a simple program interface to the data file of a clinical chemistry laboratory's computer system. This system may be used for various types of statistical data analysis based on the laboratory's routine work.
Scandinavian Journal of Clinical and Laboratory Investigation, 1978
In 430 patients with a variety of thyroid disorders, linear discriminant analysis was used to sel... more In 430 patients with a variety of thyroid disorders, linear discriminant analysis was used to select laboratory test combinations giving optimum diagnostic efficiency in thyroid function studies. Unexpectedly, TSH was found valuable in the diagnosis of hyperthyroidism and T3 in hypothyroidism. These test combinations were found optimal for the separation of euthyroidism/hyperthyroidism: T3, TSH and T4; euthyroidism/hypothyroidism: Combined free thyroid hormone index (FTI) and TSH; and hyperthyroidism/euthyroidism/hypothyroidism: T3, TSH, T4, FTI and T3U. The latter test combination had a total efficiency of 94%. Cholesterol, achilles reflex time, PBI and radioiodine uptake measurement contributed little to the discrimination.
Scandinavian Journal of Clinical and Laboratory Investigation, 1973
AbstractPyroglutamate hydrolase was partially purified from rat liver. The enzyme was found to ha... more AbstractPyroglutamate hydrolase was partially purified from rat liver. The enzyme was found to have a pH optimum at 7.5. The equilibrium constant was very high, since more than 90 per cent of pyroglutamate was hydrolyzed during prolonged incubation. The enzyme was unable to catalyze the reverse reaction. The Km of ATP was 29–36 μmol/l, and the Km of pyroglutamate was 1.2–3.3 μmol/l. The Km of both substrates were apparently independent of the second substrate. These data seem to exclude the possibility that the enzyme operates by a ping-pong mechanism.
Scandinavian Journal of Clinical & Laboratory Investigation, 1969
A 4-year material of radioiodine tests, including separation of plasma radioactivity into 4 fract... more A 4-year material of radioiodine tests, including separation of plasma radioactivity into 4 fractions, has been subjected to an extensive statistical analysis in order to evaluate the criteria for the thyroid function. ‘Normal’ ranges for various thyroid parameters were thus estimated. Two-dimensional statistical methods, including the application of bivariate tolerance areas (ellipses), were employed to test the diagnostic consequences of correlated variations between early and late radioiodine uptakes and between the fractions of plasma radioactivity. Labelled iodine in urine and iodide in plasma were dependent on age and kidney function.
Scandinavian Journal of Clinical & Laboratory Investigation, 1975
... The method is suitable for identifying the optimal composition of clinical chemical 'test... more ... The method is suitable for identifying the optimal composition of clinical chemical 'test batteries' for various ... 13. Harris, E. K. Effects of intra-and interindividual variation on the appropriate use of normal ranges ... Jackson, E. C. Missing values in linear multiple discriminant analysis. ...
CRC Critical Reviews in Clinical Laboratory Sciences, 1978
Discriminant analysis (DA) is a pattern recognition technique that has been widely applied in med... more Discriminant analysis (DA) is a pattern recognition technique that has been widely applied in medical studies. It allows multivariate observations ("patterns" or points in multidimensional space) to be allocated to previously defined groups (diagnostic categories). The relationships between DA and other multivariate statistical techniques of interest in medical studies will be briefly discussed. The main emphasis is on linear discriminant functions (LDF). The theoretic assumptions underlying DA using LDFs will be presented, and the effect of violations to these assumptions will be reviewed in detail. Alternative methods will be presented when violations cause serious problems. It has been shown that the familiar LDF is fairly robust to departures from the assumptions. The application of the LDF in less than ideal situations therefore often does not cause much harm (if the violations are not too grotesque). Another set of problems reviewed is how to estimate the misallocation probabilities when using discriminant functions. The selection of the "best" subset of variables out of the complete set will be discussed. Practical guide lines are given based on the theoretic studies reviewed. When possible, available computer programs for various problems of DA will be indicated. The review does not aim at covering all medical studies where DA has been applied, since emphasis is on the practical conclusions of the theory of DA.
Computer Methods and Programs in Biomedicine, 1995
... Non-parametric imethod; Outlier detection; Parametric method; Reference interval; Reference l... more ... Non-parametric imethod; Outlier detection; Parametric method; Reference interval; Reference limits :l. Introduction In 1970 the International Federation of Clinical ... The RefVal program only implements the simple Dixon test [5,10,13], which identifies an extremely low or high ...
Clinical Chemistry and Laboratory Medicine (CCLM), 2004
The International Federation of Clinical Chemistry (IFCC) published between 1987–91 a series of s... more The International Federation of Clinical Chemistry (IFCC) published between 1987–91 a series of six recommendations on reference values in laboratory medicine. This paper reviews the history and scope of the fifth part of these recommendations. This fifth recommendation deals with statistical methods used for analysis of reference values and estimation of reference intervals. The RefVal program, which implements the recommended method, is also described.
Total serum bile acids were estimated by an enzymic (3alpha-hydroxysteroid dehydrogenase) method ... more Total serum bile acids were estimated by an enzymic (3alpha-hydroxysteroid dehydrogenase) method in 173 fasting patients with different liver diseases, classified into 17 groups by morphological criteria. The results were not highly correlated with those for any of the other 24 tests included in the study, but moderate correlations were observed with bilirubin or alanine aminotransferase (positive) and with prealbumin (negative) in a few patient groups. The sensitivity of total bile acids in serum of fasting individuals as a liver-function test was rather high, comparable with that of serum enzymes. When discriminant analysis was used to identify optimal combinations of tests for the separation of different groups of liver diseases, we found that data on serum bile acids added some new information to that carried by the other 24 tests.
We studied the potential benefit of using artificial neural networks (ANNs) for the diagnosis of ... more We studied the potential benefit of using artificial neural networks (ANNs) for the diagnosis of thyroid function. We examined two types of ANN architecture and assessed their robustness in the face of diagnostic noise. The thyroid function data we used had previously been studied by multivariate statistical methods and a variety of pattern-recognition techniques. The total data set comprised 392 cases that had been classified according to both thyroid function and 19 clinical categories. All cases had a complete set of results of six laboratory tests (total thyroxine, free thyroxine, triiodothyronine, triiodothyronine uptake test, thyrotropin, and thyroxine-binding globulin). This data set was divided into subsets used for training the networks and for testing their performance; the test subsets contained various proportions of cases with diagnostic noise to mimic real-life diagnostic situations. The networks studied were a multilayer perceptron trained by back-propagation, and a l...
The clinician often orders more tests than the test combination necessary for solving an actual c... more The clinician often orders more tests than the test combination necessary for solving an actual clinical problem, thus increasing costs and the complexity of interpretation. The identification of optimal combinations of laboratory tests for commonly encountered or difficult clinical problems is therefore highly desirable. The authors review their experiences using multivariate analysis to identify combinations of tests that distinguish clinical categories of liver disease and of thyroid function.
Scandinavian Journal of Clinical & Laboratory Investigation, 1978
A general-purpose statistical program package (BMDP) has been linked by a simple program interfac... more A general-purpose statistical program package (BMDP) has been linked by a simple program interface to the data file of a clinical chemistry laboratory's computer system. This system may be used for various types of statistical data analysis based on the laboratory's routine work.
Scandinavian Journal of Clinical and Laboratory Investigation, 1978
In 430 patients with a variety of thyroid disorders, linear discriminant analysis was used to sel... more In 430 patients with a variety of thyroid disorders, linear discriminant analysis was used to select laboratory test combinations giving optimum diagnostic efficiency in thyroid function studies. Unexpectedly, TSH was found valuable in the diagnosis of hyperthyroidism and T3 in hypothyroidism. These test combinations were found optimal for the separation of euthyroidism/hyperthyroidism: T3, TSH and T4; euthyroidism/hypothyroidism: Combined free thyroid hormone index (FTI) and TSH; and hyperthyroidism/euthyroidism/hypothyroidism: T3, TSH, T4, FTI and T3U. The latter test combination had a total efficiency of 94%. Cholesterol, achilles reflex time, PBI and radioiodine uptake measurement contributed little to the discrimination.
Scandinavian Journal of Clinical and Laboratory Investigation, 1973
AbstractPyroglutamate hydrolase was partially purified from rat liver. The enzyme was found to ha... more AbstractPyroglutamate hydrolase was partially purified from rat liver. The enzyme was found to have a pH optimum at 7.5. The equilibrium constant was very high, since more than 90 per cent of pyroglutamate was hydrolyzed during prolonged incubation. The enzyme was unable to catalyze the reverse reaction. The Km of ATP was 29–36 μmol/l, and the Km of pyroglutamate was 1.2–3.3 μmol/l. The Km of both substrates were apparently independent of the second substrate. These data seem to exclude the possibility that the enzyme operates by a ping-pong mechanism.
Scandinavian Journal of Clinical & Laboratory Investigation, 1969
A 4-year material of radioiodine tests, including separation of plasma radioactivity into 4 fract... more A 4-year material of radioiodine tests, including separation of plasma radioactivity into 4 fractions, has been subjected to an extensive statistical analysis in order to evaluate the criteria for the thyroid function. ‘Normal’ ranges for various thyroid parameters were thus estimated. Two-dimensional statistical methods, including the application of bivariate tolerance areas (ellipses), were employed to test the diagnostic consequences of correlated variations between early and late radioiodine uptakes and between the fractions of plasma radioactivity. Labelled iodine in urine and iodide in plasma were dependent on age and kidney function.
Scandinavian Journal of Clinical & Laboratory Investigation, 1975
... The method is suitable for identifying the optimal composition of clinical chemical 'test... more ... The method is suitable for identifying the optimal composition of clinical chemical 'test batteries' for various ... 13. Harris, E. K. Effects of intra-and interindividual variation on the appropriate use of normal ranges ... Jackson, E. C. Missing values in linear multiple discriminant analysis. ...
CRC Critical Reviews in Clinical Laboratory Sciences, 1978
Discriminant analysis (DA) is a pattern recognition technique that has been widely applied in med... more Discriminant analysis (DA) is a pattern recognition technique that has been widely applied in medical studies. It allows multivariate observations ("patterns" or points in multidimensional space) to be allocated to previously defined groups (diagnostic categories). The relationships between DA and other multivariate statistical techniques of interest in medical studies will be briefly discussed. The main emphasis is on linear discriminant functions (LDF). The theoretic assumptions underlying DA using LDFs will be presented, and the effect of violations to these assumptions will be reviewed in detail. Alternative methods will be presented when violations cause serious problems. It has been shown that the familiar LDF is fairly robust to departures from the assumptions. The application of the LDF in less than ideal situations therefore often does not cause much harm (if the violations are not too grotesque). Another set of problems reviewed is how to estimate the misallocation probabilities when using discriminant functions. The selection of the "best" subset of variables out of the complete set will be discussed. Practical guide lines are given based on the theoretic studies reviewed. When possible, available computer programs for various problems of DA will be indicated. The review does not aim at covering all medical studies where DA has been applied, since emphasis is on the practical conclusions of the theory of DA.
Computer Methods and Programs in Biomedicine, 1995
... Non-parametric imethod; Outlier detection; Parametric method; Reference interval; Reference l... more ... Non-parametric imethod; Outlier detection; Parametric method; Reference interval; Reference limits :l. Introduction In 1970 the International Federation of Clinical ... The RefVal program only implements the simple Dixon test [5,10,13], which identifies an extremely low or high ...
Clinical Chemistry and Laboratory Medicine (CCLM), 2004
The International Federation of Clinical Chemistry (IFCC) published between 1987–91 a series of s... more The International Federation of Clinical Chemistry (IFCC) published between 1987–91 a series of six recommendations on reference values in laboratory medicine. This paper reviews the history and scope of the fifth part of these recommendations. This fifth recommendation deals with statistical methods used for analysis of reference values and estimation of reference intervals. The RefVal program, which implements the recommended method, is also described.
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Papers by Helge Solberg