Computational Personality Type Classification (1999-2001)

 

Rresearch funded by the Ministry of Education of Czech Republic under the research program ‘Transdisciplinary Biomedical Engineering Research’, No.  MSM 210000012.


 

This project was focused on application of artificial intelligence and pattern recognition methods to the biological data processing in the area of computational personality type classification. Five approaches to the computational personality type classification problem. In contrast to the standard personality type classification process involving psychological investigation, our approach is based on the human operator’s physiological parameters measurement (pulse frequency, systolic and diastolic blood pressures, skin resistance, muscular tonus). Personality type classification consists in neuroticism and tendency to risk behaviour classification. Five approaches were compared one to one – expert system, machine learning, combination of expert system and machine learning, fuzzy clustering, and fuzzy preference expert systems complemented by an aggregation mechanism.  The set of tested persons consisted of 60 persons in age between 18 an 30. This set embodies persons with a tendency to risk behaviour, persons with the tendency to neuroticism, and persons without any of the tendencies mentioned above. Two new classification methods were suggested.

 

Staff:

Dr. Ing. Lenka Lhotska*

Dr. Ing. Vladimir Eck

Ing. Ladislava Janku

Ing. Milan Sorf, Ph.D.

 

*Project manager

 

Publications:

-         Janku, L. - Šorf, M. - Lhotska, L. - Eck, V.: Five Approaches to the Computational Personality Classification Problem. In: Proceedings of CIMA 2001, ICSC/NAISO conference, UK, 2001

-         Janku, L. - Eck, V.: Fuzzy Distributed Reasoning about Multi-Dimensional Medical Data. In: Proceedings: MEDICON 2001. Zagreb: University of Zagreb, 2001, vol. 1, p. 441-444. ISBN 953-184-023-7.

-         Janků, L.- Lhotska, L.: Aggregation of Fuzzy Preferences as an Efficient Approach to the Computational Personality Type Classification Problem In: N. Mastorakis (Editor): Problems in Applied Mathematics and Computational Intelligence, WSES Press, 2001

-         Šorf, M. - Lhotská, L. - Janku, L. - Eck, V.: Application of the Methods AI Approaches to Personality Type Classificaion. In: Modelling, Identification and Control - volume I. Anaheim : Acta Press, 2001, vol. 1, p. 403-408. ISBN 0-88986-316-4.

-         Janků, L. - Šorf, M. - Eck, V. - Lhotská, L. - Fejtová, M. Multiple Criteria Choice Mechanism for Intelligent Man-Machine Interface. In: Proceedings of INES 2000. Vol. 1. IEEE Industrial Electronics Society. 2000. ISBN 961-6303-23-6

-         Šorf, M. - Janků, L. - Lhotská, L. - Eck, V. Applications of Expert System and Machine Learning Approach to Intelligent Man-machine Interface. In: Intelligent Techniques and Soft Computing in Nuclear Science and Engineering. Vol. 1. Singapore: World Scientific. 2000. p. 191-197. - ISBN 981-02-4356-1

 

Project Overview:

 

1. Introduction

 

Intelligent interface, which could be able to monitor and estimate human operator’s psychical state and predict his/her future behaviour, could minimize system failings caused by human factor. 

Investigations on the human’s operator psychical state monitoring and estimation have recently received remarkable attention particularly for the following applications: intelligent interface, real-time measurement and processing of physiological data, on-line human operator monitoring, and extraction of information from selected measured physiological parameters.

Other research in the area of intelligent man-machine interface has been devoted to the design of special multi-agent web based systems, which appears as a suitable solution for large internet and e-commerce systems, but which don’t provide a satisfying solution for the mentioned problem of human operator’s psychological state estimation.

The necessity of estimation and prediction of the human’s operator psychical state implies a necessity of utilization of an operator’s internal model. A task of internal model selection is closely related to the problem of human operator’s personality type classification. Particular personality type is characterized via the different mental model. It appears much more suitable to provide this classification automatically than to follow a standard way consisting in a special kind of psychological investigation. 

This approach sets a new requirement to intelligent man-machine interface. Interface must be able to classify human’s operator personality type. To solve this problem, we designed a way and a methodology how to do it. This methodology consists in several physiological parameters measurement while the tested person performs psychical or physical exercises putting a psychical stress to her or him.  This methodology is called a computational personality type classification.

Our research in essence involves application on artificial intelligence methods to the computational personality type classification problem. The major advantage of this approach towards the standard way consisting in psychological investigation was the higher objectivity and independence on the expert presence.

 

2. Computational Personality Type Classification

 

Computational personality type classification is based on assumption that it’s possible to estimate a personality type from the data obtained by monitoring the tested person’s physiological responses (pulse frequency, systolic and diastolic blood pressures, skin resistance, muscular tonus) to the different psychical load. We selected two factors on which the personality type depends - neuroticism and tendency to risk behaviour [6]. 

A classification problem can be formulated by the following question: how we can estimate the monitored features on condition we have information about the relationships between measured data and estimated features on condition, that there is no exactly given mathematical formula expressing relationship between


measured data and estimated features; only some vague rules are given.

 

3. Applied Artificial Intelligence and Soft Computing Methods

 

3.1. Expert System

 

The first approach consists in application of the expert system with knowledge base developed in a standard way. This knowledge base [1] uses as input information reaction of heart frequency, muscular activity, skin galvanic reaction, and systolic and diastolic blood pressures. The knowledge has been acquired from measured data, questionnaires and theoretical knowledge. In the process of development of the knowledge base we have started from theoretically known reactions of individual physiological quantities on psychic load. The knowledge base has been developed in traditional way – using expert knowledge. At first unstructured interview has been performed when an expert has commented the problems. Then structured interview has followed when concrete questions concerning influence of psychic load on physiological parameters for individual psychological groups have been asked. In this phase the expert has confirmed influence of psychic load on reaction of physiological quantities and has not assigned any significance to average values of physiological quantities at psychic load. Finally, we have used the method of repertoire table for knowledge acquisition. In this method objects are individual psychological groups and constructs are reactions of heart frequency, muscular activity, systolic and diastolic pressure, and skin galvanic reaction. Based on the repertoire table we have formulated rules with corresponding values of certainty measures.

The most difficult task after development of the knowledge base has been assigning values of prior probabilities to nodes and measures of necessity and sufficiency to rules. The medical doctors have not been usually able to determine more precisely how probable the given statement is. Therefore after consultations with the medical doctors, we have tried to estimate the probabilities of the nodes and rules by ourselves. The first consultations with the expert system have shown that prior probabilities of nodes and measures of necessity and sufficiency of rules have been estimated quite well; only some of them have been overestimated.

After each response from the database we have inspected updated values of probabilities of all nodes. From these values we have determined after which question and response incorrect changes of probabilities of goal hypotheses have followed and which rule has caused this change. Then we have changed values of measures of that rule and started new compilation. It has showed whether the change of the value has been correct. If not, the process has been repeated. After compilation of the knowledge base we have determined resulting success rate of the knowledge base.

Assigning values to nodes has preceded assigning values to rules that have been done during the phase of tuning the knowledge base. At first prior probabilities of goal hypotheses have been determined. Then prior probabilities of all remaining nodes have been determined.

The designed knowledge base contains 25 nodes out of which 10 are quantitative and 15 qualitative. The quantitative nodes are of 1-value type and are determined for input of physiological parameters values. Qualitative nodes are of Bayesian type – 13 are askable nodes and 2 are goal hypotheses. In leaf nodes there are questions about heart frequency reactivity, systolic and diastolic blood pressure, muscular tonus and skin resistance. Top nodes (goal hypotheses) characterize risk groups of persons (neurotics and persons with risk type of behaviour). The knowledge base contains 5 rules expressing relations between individual nodes that represent given statements on respondent’s state. Low number of rules is caused by the fact that during consultation with an expert influence of average values of physiological parameters has been underestimated and on the other hand influence of reaction of physiological parameters on psychic load has been overestimated.

There has appeared necessity to include 20 context links into the knowledge base so that the questions follow in the right order (first questions on input parameters and then on their values).

The knowledge base structure has been divided into several substructures. The substructures associate attributes that are linked together and frequently give evidence for several types of risk groups. In particular, there are three substructures: cardiovascular parameters, muscular tonus, skin resistance.

 

3.2. Machine Learning

 

This chapter describes an application of machine learning approach. For generation of the decision tree, algorithm ID3 [3] has been used. This algorithm is of TDIDT type (Top-Down Induction of Decision Tree) that constructs the decision tree recursively from the root to leaves. Original training set is thus divided into smaller and smaller subsets.

Application of learning algorithm has two phases:

·        generation of the decision tree

·        decision tree pruning

We have applied classification system [4] based on the ID3 algorithm. It does not use any prior knowledge and objects are formally represented by a list of attributes.


The system contains methods for discretization, determination of the most informative attribute and pruning.

Attributes are both discrete with low number of values and continuous. The continuous attributes have been discretized using R-binarization method. It is based on the following principle: when using binarized attribute for branching in a certain node this attribute is not excluded from the list of attributes applicable for branching in the sub-tree of the given node, but if the attribute has tendency to divide cases into more than two intervals it may appear in one branch of the decision tree several times, each time with different discretization value. In this way we reach similar effect as with direct division of the set into more subsets. Data for the training set have been selected randomly. Mántaras method [5] of determination of distance between two partitions (further called distance gain) is used for selection of the most informative attribute. We determine distance gain for all attributes. The attribute with the highest value of distance gain is placed on the position of the root node. Homogeneous branches are ended with the leaf node that is assigned name of the class. In non-homogeneous branches, the attribute with the next highest value of distance gain is looked for.

Partial goal of this work has been application of machine learning to respondent classification. Input into the classification system is the training set that forms interface between this system and the environment. The training set is composed of header and training examples. In the header, there are defined the classes into which examples will be classified and the attribute names.

 

3.3. Combination of Machine Learning and Expert System

 

Since the success rate of the knowledge base developed in the classical way is not high, we have developed new methodology of knowledge base development utilizing machine learning algorithms. The database is divided into two sets: training and testing. The knowledge base is developed using the training set and afterwards it is tested using data from the testing set. This approach is based on measured data and data acquired from the questionnaires in contrast to the classical approach where the knowledge is delivered by the expert. The rules for the knowledge base are acquired from a generated decision tree. These rules are consulted with experts, modified and completed with rules expressing influence of reactivity of physiological parameters on risk groups. Addition of further rules leads to improved behaviour of the knowledge base. We have used the same methodology for tuning and verification of the knowledge base and determination of prior probabilities of the nodes and rules as with the previous knowledge base using only expert knowledge.

This knowledge base contains 32 nodes. All nodes are qualitative, out of which 21 are logical and 11 Bayesian (9 askable and 2 goals). Askable nodes contain questions on level of average values of heart frequency, muscular tonus, skin resistance and systolic and diastolic blood pressure, completed with case-history information (coffee, alcohol and cigarette consumption, current health problems, medicament use and movement activity). The goal hypotheses are neuroticism diagnosis and risk type of behaviour diagnosis. The knowledge base contains 36 rules that express relations between individual nodes that represent given statements on respondent’s state. Rules acquired by machine learning express relations between individual risk groups and average values of physiological parameters and case-history information.

Structure of this knowledge base is composed of three substructures that associate attributes linked together and giving evidence for different types of risk groups. In the first substructure attributes connected with systolic and diastolic blood pressure are grouped, in the second substructure attributes connected with remaining physiological parameters are grouped and in the third substructure case-history information is expressed.

 

3.4. Fuzzy Clustering

 

This approach requires several stages: data pre-processing & normalisation, data fuzzyfication, application of fuzzy clustering algorithm.

Normalisation – five signals have been measured and each of them has its units.  The absolute normalisation has been used (the same value has been assign to the specific value of the particular signal in each case, e.g. the value 0.6 is assigned to pulse frequency in each case).

Case History Data Normalisation – during this phase, the information obtained from the case history questionnaire is included into normalised data. This normalisation is based on the experimental rules provided by experts. The data are re-counted in accordance to these rules to be comparable with the other ones. The aim of this step is excluding of non-linear influence of medicaments etc.

Normalised average values setting – average values have been counted in periodic intervals of several seconds. These average values are fuzzificated. 

Normalised average difference setting – average value of the particular normalised signal measured during the first rest time is set. This value is subtracted from the results obtained in the previous step. Result values are fuzzyficated.

Correlation – If the signal is valid, it has to be something correlated with the other ones.


This procedure computes correlation between pairs of signals to exclude no longer valid signal from the further processing.

A measured data fuzzyfication consists in the assigment of the one membership function grade or more ones to the each measured value. The universe set has been divided into five carriers. The universe set overlapping is not equal; the fuzzy set density is higher close to null.

The membership function has been estimated from the measured data. Well-known Fuzzy ISODATA method was applied  [8].

 

3.5. A Set of Fuzzy Preference Expert Systems and Fuzzy Aggregation Mechanism

 

When the expert system is applied to the problem of computational personality type classification, the knowledge base inconsistency is inadmissible and has to be solved during knowledge base construction. The simplest approach could be missing that information, which is regarded as the least important. Then, the rate of successfulness of the designed expert system depends something on creator’s intuition to exclude the least important information. The second great disadvantage of this quite simple approach to information inconsistency is that usually each expert is not able to give an expression to each measured physiological parameter.

To find an efficient solution, we set a little more different problem formulation towards the standard approach described in the previous text and presented on ‚Figure 1‘. Standard approach involves a construction of one knowledge base consisting of rules concerning with information given by all experts.

 

 

Figure 1: A Standard way of knowledge base construction

 

We decided not to design this well-known kind of knowledge base, but to use a few of preference expert systems [9, 10].  Standard diagnostic expert system gives an answer consisting of one alternative. Preference expert system is a special kind of diagnostic expert system, which gives the evaluation of some relation defined on the set of all possible alternatives. This relation can be fuzzy or non-fuzzy and depends mainly on structure of this preference expert system.

 

 

Figure 2: The change of the problem formulation: a set of preference expert systems and aggregation mechanism.

 

In this case, the fuzzy relation ‘Alternative (model, personality type) A is not worse than alternative (model, personality type) B for the given situation’ was used. Knowledge base of each expert system was designed to provide evaluation of this fuzzy relation; it involves knowledge and information obtained by one of the experts. The rules each knowledge base consists of needn’t be consistent with the ones included in the other knowledge bases. Input information of an individual expert system may differ from the input information of the other ones. As we said above, each preference expert system provides an evaluation of the specific – in this case fuzzy – relation. These evaluations are aggregated with respect to relation characterizing mutual relative importance of used preference expert systems (See ‚Figure 2‘).

Described approach should be formulated mathematically. We implemented a non-dominance aggregation algorithm suggested by Orlowski [12]. For detail system structure see [9].

 

4. Experiments and Results

 

4.1. Measurement Methodology

 

Psychical load has been presented to the operator both in the visual and acoustic forms. As psychical load, standard diagnostic and load tests are used. Short test description follows. The first test consists of a set of the questions investigating verbal, numeric and perceptual logic, space perception and analytic and technical skills.


Human operator is invited to answer these questions as quickly as he/she can. Naturally, the correctness is also required. The second test consists in the task of ‘number seven subtracting’. A random number between 900 and 1000 is selected. Operator is invited to subtract seven from this number, then to subtract seven from the obtained result, etc. The necessity to answer in the periodic intervals assures psychical stress genesis. The selected physiological parameters are measured during the both rest and load test phases. To obtain basic information about tested person life style, we use case history data (coffee and alcohol drinking, medicaments taking, movement activity, etc.).

Examples are classified into four classes: neurotics, persons with risk type of behaviour, neurotics and persons with risk type of behaviour, persons with negative neuroticism and persons without risk type of behaviour.

 To assure a possibility to compare and evaluate results obtained by application of the described approach, each tested person passed a psychological investigation to diagnose his/her personality type, tendency to psychotic disorder, and tendency to neurotic behaviour. This diagnosis was used as an absolute standard during the comparative evaluation. The success rate of each of designed algorithms for human operator’s personality type classification refers to this diagnosis.

 

4.2. Structures of the Training and Testing Sets

 

The set of tested persons consisted of 60 persons in age between 18 and 30. Each person could be tested several times (reason: to obtain more data). This set embodies persons with a tendency to risk behaviour, persons with the tendency to neuroticism, and persons without any of the tendencies mentioned above. 600 testing sets, each containing about 30 elements, were selected randomly from the measured data. The relative representations of neurotics, persons with the tendency to risk behaviour, and persons without any of the tendencies mentioned above were very similar in all training sets – 1% neurotics, 24% persons with the tendency to the risk behaviour, 15% neurotics with the tendency to the risk behaviour, 60% persons without any of the tendencies mentioned above. Methods, which don‘t required existence of the training set, e.g. expert system, were tested on the same test set as the other ones.

 

4.3. Expert System

 

The knowledge base utilizing knowledge about changes and reactions of physiological parameters has reached the success rate of 70 per cent for neuroticism diagnosis and 68 per cent for diagnosis of risk persons according to Bortner’s scale. The total success rate of the expert system with this knowledge base is 60 per cent.

The expert system with this knowledge base has manifested lower reaction of heart frequency and systolic blood pressure on psychic load at persons with risk type of behaviour in comparison with persons without this type of behaviour.

The results of this knowledge base have not confirmed our assumptions which has been caused by the fact that during consultation with an expert influence of average values of physiological parameters has been underestimated and on the other hand influence of reaction of physiological parameters on psychic load has been overestimated.

 

4.4. Machine Learning

 

The success rate of generated decision trees has been between 67 and 72 per cent. The best decision tree has the success rate of 79 per cent. The classification results have confirmed our assumptions about possibility to use decision trees for respondents’ classification into psychological groups with results similar to results of psychological questionnaires (Bortner scale, Eysenck questionnaire).

 

Figure 3: A rate of successfulness for the system trained on the particular training set (20 cases).

 

4.5. Combination of Machine Learning and Expert System

 

The success rate of the knowledge base developed by application of machine learning is for neuroticism diagnosis 94.9 per cent and 83 per cent for diagnosis of risk persons according to Bortner’s scale. The total success rate of the expert system with this knowledge base is 81.4 per cent.

Since this knowledge base is relatively small for verification of the developed methodology, we have repeated the process of knowledge base division into


training and testing sets with the knowledge base generated by machine learning algorithm for respondents’ classification into psychological groups with results similar to results reached by psychological questionnaires (Bortner scale, Eysenck questionnaire).

Figure 4: A rate of successfulness for the system trained on the particular training set (20 cases).

 

4.6. Fuzzy Clustering

 

The success rate of the model choice provided by the intelligent interface is about 48 % in a case of using average values of measured parameters and 55 % in a case of using values of an average difference. These values are relatively low in comparison with the success rate of another approaches. We try to suggest several possible reasons for these results obtaining. The first one is a case history data normalisation. It’s provided according to several rules obtained by experts, but there were no comparison study performed to prove validation of these rules. This step could be one of the possible error sources. The second possible error source consists in rates of the relevance of the measured signals. For example, skin-galvanic response is a better stress indicator than muscular tonus. We considered the same relevance of all measured parameters.

 

4.7 A Set of Fuzzy Preference Expert Systems and Fuzzy Aggregation Mechanism

 

Firstly, three preference expert systems were applied to all selected testing sets. Table 1 gives an overview of inputs of these systems. In this example, we consider nine possible personality types characterized by the different grade of the neuroticism and by the different grade of tendency to risk behaviour.

Let’s note, the used fuzzy relation is understood as ”not less important than”. The average success rate of this system was about 93 percent for neuroticism classification and about 90 percent for tendency to risk behaviour classification. The average success rate for the classification of personality type was about 90 percent. The successfulness of the presented approach depends mostly on the qualitative parameters of the preference expert system knowledge bases.

 

Table 1: An overview of the inputs of the applied preference expert systems

 

Input

ES1

ES2

ES3

Systolic blood pressure

YES

-

 

Diastolic blood pressure

YES

-

-

Pulse frequency

YES

YES

-

Skin-galvanic Response

-

YES

-

Muscular Tonus

-

-

YES

 

Table 2: Our relative evaluation of the importance of the applied preference expert systems, the relation ”expert system A is not less important than expert system B”

 

 

ES1

ES2

ES3

ES1

1

0.8

0.9

ES2

0.9

1

0.9

ES3

0.4

0.5

1

 

If some of the expert systems outputs of which are aggregated may not for any reason provide relation for any pair of alternatives, and other relations are evaluated as the two alternatives are the same, it can ”blur” a result. Several alternatives can be evaluated as optimal.

 

5. Conclusion

 

Results acquired by individual methods do not differ very significantly. The differences are caused by application of different methods of knowledge and data processing. The advantage of machine learning approach is that the decision tree is generated only from measured data and information from case-history questionnaire. No expert knowledge is required for these methods. However, the expert knowledge is necessary when developing a knowledge base. The expert system is fully based on expert knowledge and theoretical assumptions. Combination of expert system and machine learning joins knowledge acquired from the database of measured data, data from case-history questionnaire and knowledge acquired from experts in the given problem area. Maximum utilization of all these possibilities brings the best results. From these reasons, machine learning is more suitable for data sets with great number of attributes than expert system. If we have a data set with small number of attributes, advantages of machine learning are decreasing. In such case expert system is more advantageous.


However, in both cases combination of expert system and machine learning is the best solution because it reaches the same quality as better of both methods and more over it is strengthened by advantages of the other method.

Machine learning need for credibility of results large volume of data, of which one part is used for generation of the decision tree, and the other one for testing. The advantage of expert system is its applicability with small data sets, because expert knowledge is used for development of the knowledge base and data set is used for testing. Combination of expert system and machine learning is applicable for both large and small data sets thanks to combination of advantages and properties of both methods.

Fuzzy clustering appears as the least suitable among the compared approaches. The reason for the relative low rate of successfulness seems to be normalisation process or considering the same relevance of all measured parameters.

Last approach is based on an application of the aggregation of the individual fuzzy preferences into one fuzzy relation with respect to information about relative importance of individual attributes characterizing each of the alternatives. These attributes are obtained from the fuzzy preference expert systems that are able to provide independent comparative evaluation of all alternatives. There is also available relation describing importance of the expert systems and thus expressing significance of individual attributes. Input information of an individual expert system is different from the input information of the other ones. The rules each knowledge base consists of needn’t be consistent with the ones included in the other knowledge bases. For each pair of models A and B, each expert system supplies evaluation of the relation "model A is not worse than model B for the given situation". These evaluations are aggregated with respect to relation characterizing mutual relative importance of used expert systems. This approach enables not only to perform choice for a set of alternatives but also to include views of several experts into decision making while incorporation of a new expert system into the current system can be done more or less without any problems.

 

References

 

[1]      Y. Kodratoff, Introduction to Machine Learning (London: Pitman, 1988).

[2]      J. R. Quinlan, Probabilistic Decision Trees. Machine Learning: An Artificial Intelligence Approach, Volume III  (San Mateo: Morgan-Kaufmann, 1990).

[3]      R. S. Michalski, Learning Flexible Concepts: Fundamental Ideas and a Method Based on Two-Tiered Representation. Machine Learning: An Artificial Intelligence Approach, Volume III (San Mateo: Morgan-Kaufmann, 1990).

[4]      R. Mántaras, A Distance-Based Attribute Selection Measure for Decision Tree Induction (Boston: Kluwer Academic Publishers, 1991).

[5]      Eysenck, H.J, The Structure of Human Personality, 2nd edition, London 1960

[6]      Fodor, J., Ovchinnikov, S.: On aggregation of t-transitive fuzzy binary relations, in Fuzzy Sets and Systems, 72:135-145, 1995

[7]      Gath, I., Geva, A.: Unsupervised fuzzy clustering, IEEE Transactions PAMI, 11, 7, 1989, 773-781

[8]      Janků, L., Lhotská, L..: Aggregation of Fuzzy Preferences as an Efficient Approach to the Computational Personality Type Classification Problem,  in Masorkais, N. (Ed.): Problems in Applied Mathematics and Computational Intelligence, ISBN 960-8052-30-0

[9]      Janků, L., Šorf, M., Eck, V.: Preliminary Phase of Co-operation between Human Operator and Intelligent Interface - Computational Personality Type Classification, research report, BIO 333-09/00. ČVUT FEL, Praha, 38 pp., 2000

[10]  Ovchinnikov, S.: Means and social welfare functions in fuzzy binary relation spaces. In Kacprzyk, J. and Fedrizzi, M.: Multiperson Decision Making Using Fuzzy Sets and Possibility Theory, 143/154, Kluwer

[11]  Orlovski, S.: Calculus of decomposable properties, fuzzy sets and decisions, Allerton Press, 1994

[12]  Šorf, M., Janků, L., Lhotská, L., Eck, V.: Applications of Expert System and Machine Learning Approach to Intelligent Man-machine Interface. In: Intelligent Techniques and Soft Computing in Nuclear Science and Engineering. Vol. 1. Singapore: World Scientific. p. 191-197. - ISBN 981-02-4356-1, 2000