Factor Analysis
Data Base

Factor analysis in Chromatography

1. H. Gao, T. Li, K. Chen and S. Lin "A novel approach of initial vectors construction in iterative target transformation factor analysis" Talanta 68, 3, 542-548 (2006)

1. P. Forlay-Frick, J. Fekete and K. Héberger "Classification and replacement test of HPLC systems using principal component analysis" Analytica Chimica Acta 536, 1-2, 71-81 (2005)
2. K. Héberger, K. Milczewska and A. Voelkel "Principal component analysis of polymer-solvent and filler-solvent interactions by inverse gas chromatography" Colloids and Surfaces A: Physicochemical and Engineering Aspects 260, 1-3, 29-37 (2005)
3. M. Wasim and R.G. Brereton "Application of evolving factor analysis to on-flow LC-NMR data using spectral windows" Chemometrics and Intelligent Laboratory Systems 78, 1-2, 51-62 (2005)
4. Y.F. Zhu and Y. He "[Study on applying principle component analysis to data processing on chromatographic fingerprints for Pinellia Cum Bile]" Zhongguo Zhong Yao Za Zhi 30, 14, 1089-1091 (2005)

1. I. García, L. Sarabia, M.C. Ortiz and J.M. Aldama "Robustness of the extraction step when parallel factor analysis (PARAFAC) is used to quantify sulfonamides in kidney by high performance liquid chromatography-diode array detection (HPLC-DAD)" Analyst 129, 8, 766-771 (2004)
2. W. Gutleben, V. Unterholzner, D. Volgger and A. Zemann "Characterization of Carbohydrates in Paper and Paper Pulps Using Anion Exchange Chromatography and Principal Component Analysis" Microchimica Acta 146, 2, 111-117 (2004)
3. M.E. Pate, M.K. Turner, N.F. Thornhill, and N.J. Titchener-Hooker "Principal component analysis of nonlinear chromatography" Biotechnology Progress 20, 1, 215-222 (2004)
4. S. Rocha, L. Maeztu, A. Barros, C. Cid and M.A Coimbra "Screening and distinction of coffee brews based on headspace solid phase microextraction/gas chromatography/principal component analysis" Journal of the Science of Food and Agriculture 84, 1, 43-51 (2004)
5. K. Wiberg, M. Andersson, A. Hagman and S.P. Jacobsson "Peak purity determination with principal component analysis of high-performance liquid chromatography–diode array detection data" Journal of Chromatography A 1029, 1-2, 13-20 (2004)
6. K. Wiberg and S.P. Jacobsson "Parallel factor analysis of HPLC-DAD data for binary mixtures of lidocaine and prilocaine with different levels of chromatographic separation" Analytica Chimica Acta 514, 2, 203-209 (2004)
7. P.V. van Zomeren , A. Hoogvorst , P.M.J. Coenegracht and G.J. de Jong "Optimisation of high-performance liquid chromatography with diode array detection using an automatic peak tracking procedure based on augmented iterative target transformation factor analysis" Analyst 129, 3, 241-248 (2004)

1. P. Doble, M. Sandercock, E. Du Pasquier, P. Petocz, C. Roux and M. Dawson "Classification of premium and regular gasoline by gas chromatography/mass spectrometry, principal component analysis and artificial neural networks" Forensic Science International 132, 1, 26-39 (2003)
2. M.R. Euerby, A.P. McKeown and P. Petersson "Chromatographic classification and comparison of commercially available perfluorinated stationary phases for reversed-phase liquid chromatography using Principal Component Analysis" Journal of Separation Science 26, 3-4, 295-306 (2003)
3. M.R. Euerby and P. Petersson "Chromatographic classification and comparison of commercially available reversed-phase liquid chromatographic columns using principal component analysis." Journal of Chromatography A 994, 1-2, 13-36 (2003)
4. E. Marengo, E. Robotti, P.G. Righetti and F. Antonucci "New approach based on fuzzy logic and principal component analysis for the classification of two-dimensional maps in health and disease. Application to lymphomas" Journal of Chromatography A 1004, 1-2, 13-28 (2003)
5. M.J. Rodriguez-Cuesta, R. Boqué and F.X. Rius "Influence of selectivity and sensitivity parameters on detection limits in multivariate curve resolution of chromatographic second-order data" Analytica Chimica Acta 476, 1, 111-122 (2003)
6. Zhong-Da Zeng, Cheng-Jian Xu, Yi-Zeng Liang, and Bo-Yan Li "Sectional moving window factor analysis for diagnosing elution chromatographic patterns" Chemometrics and Intelligent Laboratory Systems 69, 1-2, 89-101 (2003)

1. D. Bylund, R. Danielsson, G. Malmquist and K.E. Markides "Chromatographic alignment by warping and dynamic programming as a pre-processing tool for PARAFAC modelling of liquid chromatography–mass spectrometry data" Journal of Chromatography A 961, 2, 237-244 (2002)
2. E. Comas, R.A. Gimeno, J. Ferré, R.M. Marcé, F. Borrull and F.X. Rius "Time shift correction in second-order liquid chromatographic data with iterative target transformation factor analysis" Analytica Chimica Acta 470, 2, 163-173 (2002)

1. C.Y. Airiau, H. Shen and R.G. Brereton "Principal component analysis in liquid chromatography proton nuclear magnetic resonance: differentiation of three regio-isomers" Analytica Chimica Acta 447, 1-2, 199-210 (2001)
2. K. Heberger, K. Milczewska and A. Voelkel "Principal component analysis of polarity and interaction parameters in inverse gas chromatography" Journal of Chromatographic Science 39, 9, 375-384 (2001)
3. A.A. Kher, E.V. Green and M.I. Mulholland "Evaluation of principal components analysis with high-performance liquid chromatography and photodiode array detection for the forensic differentiation of ballpoint pen inks" Journal of Forensic Sciences 46, 4, 878-883 (2001)
4. C. Mason, M. Maeder, and A. Whitson "Resolving Factor Analysis" Analytical Chemistry 73, 7, 1587-1594 (2001)
5. C. Sârbu, K. Kuhajda and S. Kevresan "Evaluation of the lipophilicity of bile acids and their derivatives by thin-layer chromatography and principal component analysis" Journal of Chromatography A 917, 1-2, 361-366 (2001)

1. G. Xu, H.R. Schmid, X. Lu, H.M. Liebich and P. Lu "Excretion pattern investigation of urinary normal and modified nucleosides of breast cancer patients by RP-HPLC and factor analysis method" Biomedical Chromatography 14, 7, 459-463 (2000)

1. J. Barbosa, I. Marqués, D. Barrón and V. Sanz-Nebot "The application of factor analysis to solvatochromic parameters and pH_s values for the standardization of potentiometric sensors in mobile phases used in liquid chromatography" TrAC Trends in Analytical Chemistry 18, 8, 543-549 (1999)
2. D. Chen and H. Shen "[Dual window factor analysis for data of hyphenated chromatography]" Se Pu 17, 4, 319-322 (1999)
3. K. Héberger "Evaluation of polarity indicators and stationary phases by principal component analysis in gas–liquid chromatography" Chemometrics and Intelligent Laboratory Systems 47, 1, 41-49 (1999)
4. K. Héberger and M. Görgényi "Principal component analysis of Kováts indices for carbonyl compounds in capillary gas chromatography" Journal of Chromatography A 845, 1-2, 21-31 (1999)
5. K. Héberger, A. Keszler and M. Gude "Principal component analysis of measured quantities during degradation of hydroperoxides in oxidized vegetable oils" Lipids 34, 1, 83-92 (1999)
6. L. Giacomelli, H. Boggetti, H. Agnelli, R. Cattana and J.J. Silber "Factor analysis applied to the study of retention mechanism of nitroanilines in normal phase high performance liquid chromatography" Analytica Chimica Acta 402, 1-2, 285-295 (1999)
7. M.T. Lohnes, R.D. Guy and P.D. Wentzell "Window target-testing factor analysis: theory and application to the chromatographic analysis of complex mixtures with multiwavelength fluorescence detection" Analytica Chimica Acta 389, 1-3, 95-113 (1999)
8. R. Manne, H. Shen and Y. Liang "Subwindow factor analysis" Chemometrics and Intelligent Laboratory Systems 45, 1-2, 171-176 (1999)
9. I. Marqués, G. Fonrodona, S. Butí and J. Barbosa "Solvent effects on mobile phases used in liquid chromatography: factor analysis applied to protonation equilibria and solvatochromic parameters" TrAC Trends in Analytical Chemistry 18, 7, 472-479 (1999)
10. K.D. Zissis, R.G. Brereton and S. Dunkerley "Principal components scores and loadings plots for visualisation of the electrospray ionisation liquid chromatography mass spectra of a mixture of chlorophyll degradation products at different cone voltages" Rapid Communications in Mass Spectrometry 13, 17, 1755-1761 (1999)

1. J.L. Beltrán, J. Guiteras and R. Ferrer "Parallel factor analysis of partially resolved chromatographic data. Determination of polycyclic aromatic hydrocarbons in water samples" Journal of Chromatography A 802, 2, 263-275 (1998)
2. E. Bolzacchini, V. Consonni, R. Lucini, M. Orlandi and B. Rindone "High-performance size-exclusion chromatographic behaviour of substituted benzoylpoly-_L-lysines by principal component analysis and molecular dynamics simulation" Journal of Chromatography A 813, 2, 255-265 (1998)
3. R.G. Brereton and D.V. McCalley "Evaluation procedures for reversed-phase high-performance liquid chromatographic columns in the analysis of strongly basic compounds using principal components analysis for data assessment" Analyst 123, 6, 1175-1185 (1998)
4. G.A. Csiktusnádi-Kiss, E. Forgács, M. Markuszewski and S. Balogh "Application of multivariate mathematical-statistical methods to compare reversed-phase thin-layer and liquid chromatographic behaviour of tetrazolium salts in Quantitative Structure-Retention Relationships (QSRR) studies" Analusis 26, 10, 400-406 (1998)
5. E. Forgács and T. Cserháti "Use of principal component analysis for studying the separation of pesticides on polyethylene-coated silica columns" Journal of Chromatography A 797, 1-2, 33-39 (1998)
6. C. Sârbu and S. Todor "Determination of lipophilicity of some non-steroidal anti-inflammatory agents and their relationships by using principal component analysis based on thin-layer chromatographic retention data" Journal of Chromatography A 822, 2, 263-269 (1998)
7. X. Shao and W. Cai "Resolution of multicomponent chromatograms by window factor analysis with wavelet transform preprocessing" Journal of Chemometrics 12, 2, 85-93 (1998)
8. M. Statheropoulos, N. Tzamtzis and K. Mikedi "Short column gas chromatography–mass spectrometry and principal component analysis for the identification of coeluted substances in doping control analysis" Journal of Chromatography B: Biomedical Sciences and Applications 706, 2, 245-251 (1998)

1. P. Hindmarch, K. Kavianpour and R.G. Brereton "Evaluation of Parallel Factor Analysis for the Resolution of Kinetic Data by Diode-array High-performance Liquid Chromatography" Analyst 122, 9, 871-877 (1997)
2. A. Nasal, A. Bucinski, L. Bober and R. Kaliszan "Prediction of pharmacological classification by means of chromatographic parameters processed by principal component analysis" International Journal of Pharmaceutics 159, 1, 43-55 (1997)

1. A.G. Frenich, M.M. Galera, J.L.M. Vidal and M.D.G. Garcia "Partial least-squares and principal component regression of multi-analyte high-performance liquid chromatography with diode-array detection" Journal of Chromatography A 727, 1, 27-38 (1996)
2. C. Ritter, J.A. Gilliard, J. Cumps and B. Tilquin "Corrections for heteroscedasticity in window evolving factor analysis" Analytica Chimica Acta 318, 2, 125-136 (1996)
3. M. Statheropoulos, E. Smaragdis, N. Tzamtzis and C. Georgakopoulos "Principal component analysis for resolving coeluting substances in gas chromatography-mass spectrometry doping control analysis" Analytica Chimica Acta 331, 1-2, 53-61 (1996)
4. H. Wilcken and H-R. Schulten "Differentiation of resin-modified paints by pyrolysis-gas chromatography/mass spectrometry and principal component analysis" Fresenius' Journal of Analytical Chemistry 355, 2, 157-163 (1996)

1. R.G. Brereton, Stephen P. Gurden and J.A. Groves "Use of eigenvalues for determining the number of components in window factor analysis of spectroscopic and chromatographic data" Chemometrics and Intelligent Laboratory Systems 27, 1, 73-87 (1995)
2. T. Cserháti and E. Forgács "Thin layer chromatography and principal component analysis for the study of the interaction of amino acids with some antisense nucleosides " Analytica Chimica Acta 316, 1, 105-110 (1995)
3. A.K. Elbergali and R.G. Brereton "Influence of predicted elution regions on the performance of methods for evolutionary factor analysis as applied to high-performance liquid chromatography" Chemometrics and Intelligent Laboratory Systems 27, 1, 55-71 (1995)
4. M. Elomaa, C.H. Lochmüller, M. Kaljurand and M. Koel "Application of evolving factor analysis in thermochromatography" Chemometrics and Intelligent Laboratory Systems 30, 1, 129-132 (1995)
5. M. Koel, M. Kaljurand, C.H. Lochmueller and M. Moebus "Factor analytical resolution of simultaneous, dynamic thermal process in thermochromatography of oil shale" Chemometrics and Intelligent Laboratory Systems 30, 1, 173-178 (1995)

1. E. Forgács "Comparison of reversed-phase chromatographic systems with principal component and cluster analysis" Analytica Chimica Acta 296, 3, 235-241 (1994)
2. U. Haldna, J. Pentchuk, M. Righezza and J.R. Chrétien "Factor analysis in ion chromatography of carboxylate ions" Journal of Chromatography A 670, 1-2, 51-58 (1994)
3. G. Malmquist and R. Danielsson "Alignment of chromatographic profiles for principal component analysis: a prerequisite for fingerprinting methods" Journal of Chromatography A 687, 1, 71-88 (1994)
4. C.J. Weatherell and E.P.C. Lai "Factorial experimental design and principal component analysis of the interaction of animal glues with polymeric and silica-based stationary phases in size exclusion chromatography" Journal of Chromatography A 669, 1-2, 31-44 (1994)

1. K.J. Schostack and E.R.Malinowski "Investigation of window factor analysis and matrix regression analysis in chromatography" Chemometrics and Intelligent Laboratory Systems 20, 2, 173-182 (1993)
2. S.J. Vanslyke and P.D. Wentzell "Limitations of evolving principal component innovation analysis for peak purity detection in chromatography" Chemometrics and Intelligent Laboratory Systems 20, 2, 183-195 (1993)

1. J.R. Chrétien, M. Righezza, A.Hassani and B.Y. Meklati "Factor analysis and experimental design in high-performance liquid chromatography. XIII. Correspondence factor analysis of the heterogeneity of the behaviour of congeneric solutes series studied on homogeneous OV phases in gas chromatography" Journal of Chromatography A 609, 1-2, 261-267 (1992)
2. H.R. Keller and D.L. Massart "Artefacts in evolving factor analysis-based methods for peak purity control in liquid chromatography with diode-array detection" Analytica Chimica Acta 263, 1-2, 21-28 (1992)
3. H.R. Keller and D.L. Massart "Evolving factor analysis" Chemometrics and Intelligent Laboratory Systems 12, 3, 209-224 (1992)
4. H.R. Keller, D.L. Massart, P. Kiechle and F. Erni "Effect of the scan time on methods based on evolving factor analysis in liquid chromatography" Analytica Chimica Acta 256, 1, 125-131 (1992)
5. H.R. Keller, D.L. Massart, Y.Z. Liang and O.M. Kvalheim "Evolving factor analysis in the presence of heteroscedastic noise" Analytica Chimica Acta 263, 1-2, 29-36 (1992)
6. H.R. Keller, D.L. Massart, Y.Z. Liang and O.M. Kvalheim "A comparison of the heuristic evoling latent projections and evolving factor analysis methods for peak purity control in liquid chromatography with photodiode array detection" Analytica Chimica Acta 267, 1, 63-71 (1992)

1. J.F. Faigle, R.J. Poppi, I.S. Scarminio and R.E. Bruns "Multi-component principal component regression and partial least-squares analyses of overlapped chromatographic peaks" Journal of Chromatography A 539, 1, 123-132 (1991)
2. M. Righezza and J.R. Chrétien "Factor analysis and experiment design in high-performance liquid chromatography. X. Chemometric characterization of packings, solvents and solutes with hierarchical ascending classification and correspondence factor analysis" Journal of Chromatography A 544, 393-411 (1991)
3. M. Righezza and J.R. Chrétien "Factor analysis and experimental design in high-performance liquid chromatography XI. Factor analysis maps and chromatographic information" Journal of Chromatography A 556, 1-2, 169-180 (1991)
4. S.A. Stout "Principal components analysis of quantitative pyrolysis-gas chromatography and organic petrographic data of kerogens" Journal of Analytical and Applied Pyrolysis 18, 3-4, 277-292 (1991)
5. M.C.J. Wilce, M.I. Aguilar and M.T.W. Hearn "High-performance liquid chromatography of amino acids, peptides and proteins. CX. Principal component analysis of four sets of group retention coefficients derived from reversed-phase high-performance liquid chromatography of peptides" Journal of Chromatography A 548, 105-116 (1991)

1. H.T. Hove, O. Grahl-Nielsen and A. Rogstad "Assay for dinoflagellate toxins in mussels by gas chromatography and principal components analysis" Analytica Chimica Acta 222, 1, 35-42 (1989)
2. B. Walczak, M. Dreux, J.R. Chrétien, L. Morin-Allory, M. Lafosse and G. Felix "Factor analysis and experiment design in high-performance liquid chromatography. VIII. Charge-transfer versus standard stationary phases in normal-phase high-performance liquid chromatography" Journal of Chromatography A 464, 237-249 (1989)

1. M. Maeder and A. Zilian "Evolving factor analysis, a new multivariate technique in chromatography" Chemometrics and Intelligent Laboratory Systems 3, 3, 205-213 (1988)

1. E. Fernández-Sánchez, J.A. García-Domínguez, V. Menéndez, J.M. Santiuste and E. Pertierra-Rimada "Reduction of the number of characterizing probes in gas chromatography by factor analysis" Journal of Chromatography A 402, 318-322 (1987)
2. G. Musumarra, G. Scarlata, G. Romano, G. Cappello, S. Clementi and G. Giulietti "Qualitative organic analysis. Part 2. Identification of drugs by principal components analysis of standardized TLC data in four eluent systems and of retention indices on SE 30" Journal of Analytical Toxicology 11, 4, 154-163 (1987)
3. K. Szymoniak "Factor analysis of trends in selectivity in gas––liquid chromatography of 175 saturated and unsaturated esters on 14 polysiloxane stationary phases" Journal of Chromatography A 404, 11-22 (1987)
4. B. Walczak, J.R. Chrétien, M. Dreux, L. Morin-Allory and M. Lafosse "Factor analysis and experiment design in high-performance liquid chromatography IV. Influence of mobile phase modifications on the selectivity of chalcones on an ODS stationary phase" Chemometrics and Intelligent Laboratory Systems 1, 2, 177-189 (1987)
5. B. Walczak, L. Morin-Allory, M. Lafosse, M. Dreux and J.R. Chrétien "Factor analysis and experiment design in high-performance liquid chromatography VII. Classification of 23 reversed-phase high-performance liquid chromatographic packings and identification of factors governing selectivity" Journal of Chromatography A 395, 183-202 (1987)

1. J.R. Chrétien, B. Walczak, L. Morin-Allory, M. Dreux and M. Lafosse "Factor analysis and experiment design in high-performance liquid chromatography. VI. Comparison of the retention mechanism for fourteen octadecylsilica packings" Journal of Chromatography A 371, 253-267 (1986)
2. M.O. Eide, O.M. Kvalheim and N. Telnaes "Routine analyses of crude oil fractions by principal component modelling of gas chromatographic profiles" Analytica Chimica Acta 191, 433-437 (1986)
3. D.G. Howery, G.D. Williams and N. Ayala "Predicting retention data by target factor analysis and multiple regression analysis" Analytica Chimica Acta 189, 339-351 (1986)
4. M. Maeder and A.D. Zuberbuehler "The resolution of overlapping chromatographic peaks by evolving factor analysis" Analytica Chimica Acta 181, 287-291 (1986)
5. B. Walczak, M. Dreux, J.R. Chrétien, K. Szymoniak, M. Lafosse, L. Morin-Allory and J.P. Doucet "Factor analysis and experiment design in high-performance liquid chromatography I. Trends in selectivity of 53 chalcones in reversed-phase high-performance liquid chromatography on alkyl- or phenyl-bonded stationary phases" Journal of Chromatography A 353, 109-121 (1986)
6. B. Walczak, J.R. Chrétien, M. Dreux, L. Morin-Allory, M. Lafosse, K. Szymoniak and F. Membrey "Factor analysis and experiment design in high-performance liquid chromatography II. Normal-phase high-performance liquid chromatography on columns of different polarities" Journal of Chromatography A 353, 123-137 (1986)
7. B. Walczak, M. Lafosse, J.R. Chrétien, M. Dreux and L. Morin-Allory "Factor analysis and experiment design in high-performance liquid chromatography V. Selectivity of chalcone configuration isomers on 23 reversed-phase packings" Journal of Chromatography A 369, 27-37 (1986)
8. B. Walczak, L. Morin-Allory, J.R. Chrétien, M. Lafosse and M. Dreux "Factor analysis and experiment design in high-performance liquid chromatography III. Influence of mobile phase modifications on the selectivity of chalcones on a diol stationary phase" Chemometrics and Intelligent Laboratory Systems 1, 1, 79-90 (1986)

1. M. D'amboise and D. Noel "Use of factor analysis and liquid chromatography to determine the number of species in reactions of potassium ions with selected polyethers" Analytica Chimica Acta 170, 255-264 (1985)
2. G. Musumarra, G. Scarlata, G. Cirma, G. Romano, S. Palazzo, S. Clementi and G. Giulietti "Qualitative organic analysis. I. Identification of drugs by principal components analysis of standardized thin-layer chromatographic data in four eluent systems" Journal of Chromatography A 350, 151-168 (1985)
3. Z. Szigeti, T. Cserháti and B. Bordas "Principal component analysis for a better understanding of the herbicidal effectivity of some benzonitriles" General Physiology and Biophysics 4, 3, 321-330 (1985)

1. C.L. De Ligny, M.C. Spanjer, J.C. Van Houwelingen and H.M. Weesie "Three-mode factor analysis of data on retention in normal-phase high-performance liquid chromatography" Journal of Chromatography A 301, 3, 311-324 (1984)
2. G. Musumarra, G. Scarlata, G. Cirma, G. Romano, S. Palazzo, S. Clementi and G. Giulietti "Application of principal components analysis to the evaluation and selection of eluent systems for the thin-layer chromatography of basic and neutral drugs" Journal of Chromatography A 295, 31-47 (1984)

1. M. McCue and E.R. Malinowski "Target factor analysis of the ultraviolet spectra of unresolved liquid chromatographic fractions" Applied Spectroscopy 37, 5, 463-469 (1983)
2. G. Musumarra, G. Scarlata, G. Ramano and S. Clementi "Identification of drugs by principal components analysis of Rf data obtained by TLC in different eluent systems" Journal of Analytical Toxicology 7, 6, 286-292 (1983)

1. R. Fellous, D.L. De Micheaux, L. Lizzani-Cuvelier and R. Luft "Comportement chromatographique de phases stationaires. II. Application de l'analyse factorielle" Journal of Chromatography A 248, 1, 35-47 (1982)
2. E.R. Malinowski "Obtaining the key set of typical vectors by factor analysis and subsequent isolation of component spectra" Analytica Chimica Acta 134, 129-137 (1982)

1. M.E. Hohn, N.W. Jones and R. Patience "Objective comparison of mass fragmentograms by principal components analysis: method and results" Geochimica et Cosmochimica Acta 45, 7, 1131-1140 (1981)

1. E.R. Malinowski "Theory of error applied to factor loadings resulting from combination target factor analysis" Analytica Chimica Acta 122, 3, 327-330 (1980)

1. C.S. Gutteridge, H.J.H. MacFie and J.R. Norris "Use of principal components analysis for displaying variation between pyrograms of micro-organisms" Journal of Analytical and Applied Pyrolysis 1, 1, 67-76 (1979)
2. J.M. Halket "Factor analysis of repetitively scanned spectra in gas chromatography-mass spectrometry. The number of components in partially resolved peaks" Journal of Chromatography A 175, 2, 229-241 (1979)

1. R.B. Selzer and D.G. Howery "Factor analysis of solute parameters in ether-stationary phase interactions" Journal of Chromatography A 115, 1, 139-151 (1975)

1. P.H. Weiner, C.J. Dack and D.G. Howery "Retention index-structure relationships for alcohols using factor analysis" Journal of Chromatography A 69, 2, 249-260 (1972)