marketing research

Philosophical Foundations of Marketing Research

1. Introduction

 ‘We are people thinking about people and giving a lot of emphasis to how they perceive themselves and their relations to the outside world and the products they consume.’

                                                                                                            (Levy, 2005; p.344)

In the sentence above, by using ‘we’, Levy (2005) probably implied researchers who seek knowledge in several disciplines like psychology, sociology, anthropology, economy, management, and marketing. Although these researches are dealing with different disciplines, there is a common characteristic that all of them have; ‘curiosity’. This curiosity drives them to conduct their researches in their own discipline by their own methodologies. Although the aim of each researcher is the same which is ‘gaining knowledge’ (Hudson and Ozanne; 1988), because of different approaches and methodologies used in research processes different epistemological and ontological philosophies emerged.

This paper aims to review different philosophical perspectives and methodologies in scientific research process and determine the philosophy behind the general perspective and methodology of research process in marketing science. In order to determine the philosophical foundations of research in marketing science, study will track following steps;

  • In the first part, general perspectives in scientific research process will be analyzed (Holbrook, Morris and Shaughnessy, 1988; Hudson and Ozanne, 1988; Shankar and Goulding, 2001; Cova and Elliott, 2008)
  • In the second part, different methodologies in scientific research process will be analyzed (Deshpande, 1983; Guba and Lincoln, 1994; Levy, 2005; Sobh and Perry, 2005)
  • In the third part, scope of marketing and philosophical debates in marketing’s literature will be examined
  • In the final part, ideas obtained from first and second part will be compared with the ideas that is presented in the third part and finally philosophy behind general perspective and methodology of marketing research is tried to be determined

In this study, research process will be processed in two parts; firstly dominating perspectives in research process -positivism and interpretivism- will be presented. In the second part; quantitative methodology that is emerged from positivistic perspective and qualitative methodology that is emerged from interpretivistic perspective will be analyzed. Figure 1 represents different philosophical perspectives and methodologies in a research process


- Philosophical Perspectives and Methodologies in a Research Process

Figure 1: Philosophical Perspectives and Methodologies in a Research Process


2. Philosophical Perspectives in Scientific Research Process

This study is aiming to analyze different philosophical perspectives and methodologies in research process of marketing science. That’s why, in order to evaluate philosophical foundations of marketing research, in this part of the study, different philosophical perspectives in a scientific research process are presented.

When philosophy behind research process is analyzed, different views and perspectives are detected. For instance, Guba andLincoln (1994) put forward four different research paradigms which are positivism, postpositivism, critical theory and constructivism. Similarly, Sobh and Perry (2005) divided major philosophical paradigms behind scientific research into four as; positivism, realism, constructivism and critical theory. However, this study uses Hudson and Ozanne’s approach (1998) and combined most of the perspectives in the literature under two dominating paradigms which are positivism and interpretivism.

Hudson and Ozanne (1998) evaluated positivism and interpretivism as two dominant perspectives in research process, and they combined other emerged perspectives that are akin under these two approaches. For instance, approaches like, logical positivism, logical empiricism, the received view and objectivism are grouped under positivism label; likewise, subjectivism, phenomenology and hermeneutics are grouped under interpretivism label. According to them, differences among these debating philosophies arose in four major subjects; epistemological differences, ontological differences, having different goals and methodological differences.

Ontologically, while positivists believe that there is a single, objective reality is ‘out there’ that is independent from individual’s perception and the researcher is independent of that reality; interpretivists deny one reality approach and believe that; reality depends on perception and thus there are multiple realities according to different perceptions of people (Hudson and Ozanne, 1998; Shankar and Goulding, 2001; Tadajewski, 2006; Cova and Elliott, 2008). Also interpretivist approach emphasize that reality is ‘socially’ constructed through a human and social interaction process (Burrell and Morgan, 1979; Shankar and Goulding, 2001; Tadajewski, 2006; Cova and Elliott, 2008). When the nature of social beings is taken into account; positivists believe that human behavior is determined and individuals behave reactively, on the other hand, interpretivists believe that people interact with each other to shape their environment and they behave actively (Morgan and Smircich, 1980; Rubinstein, 1981; Hudson and Ozanne, 1998). For example, positivists believe discounts lead a change in purchase decision of an individual where interpretivists believe that discounts lead individuals to interact with each other to show their selves as smart, cost efficient shoppers.

When differences between goals of positivist and interpretivist perspectives are the issue; according to Hudson and Ozanne (1998), positivism aims to reach an explanation by predictions where interpretivism aims to reach an understanding and they evaluate this understanding process as ‘never-ending’. In other words, as Denzin asserted (1984), one never achieves the understanding, where one achieves an understanding (Hudson and Ozanne, 1998, p.510). Interpretivists believe that since ‘truth’ cannot be proven, their goal is is hermeneutic understanding or verstehen (Shankar and Goulding, 2001). ‘Verstehen’ can be defined as the overriding goal that separates social sciences from the physical sciences by providing access to the ‘human aspects of individuals’ (Wax, 1967; Hudson and Ozanne, 1998, p.510)

Epistemologically, according to Hudson and Ozanne (1998), positivists are chasing general laws that can be applied to infinitely number of phenomena, where interpretivists are seeking to determine specific phenomenon that is time and context bound. That’s because Hudson and Ozanne (1998) divided approaches into two and evaluated positivism as a ‘generalistic’ and interpretivism as a ‘particularistic’ approach. On the other hand, while positivists believe in ‘causality’ when human actions are the subject (Orlikowski and Baroudi, 1991), interpretivists believe in multiple and simultaneous shaping (Guba and Lincoln, 1994). Finally, although positivists see the researcher independent from the subject (Hudson and Ozanne, 1998),   interpretivists see the researcher as the participant of the research process since they believe that; knowledge cannot being obtained externally in an objective position Tadajewski, 2006; Cova and Elliott, 2008)

Methodologically, as general research process (Hudson and Ozanne, 1998), positivists believe in a step by step research protocol (Campbell and Stanley, 1963) and they believe that controlled experiments lead to discover causal relationships (Kerlinger, 1986). In contrast, interpretivists evaluate research process as continually evolving process and rather than controlled experiments, they believe that; researches should be conducted in natural environment (Hudson and Ozanne, 1998). When data gathering techniques are taken into account, although most of the studies associated quantitative technique with positivism (Becker and Niehaves, 2007) and qualitative technique with interpretivism (Tadajewski, 2006; Cova and Elliott, 2008), both techniques can be and are used in both approaches (Hudson and Ozanne, 1998).

All in a word, table 1 represents all the assumptions that are mentioned above regarding positivist and interpretivist approaches.

  Ontological Epistemological Goals Methodology
Positivism -Single & objective reality-Individuals behave reactively -Generalistic approach-Causality

-Independent researcher

Explanation Generally Quantitative
Interpretivism -Multiple, subjective, social constructed realities-Individuals behave actively -Particularisticapproach

– Multiple and simultaneous shaping

-Participant researcher

Understanding GenerallyQualitative

Table 1: Assumptions of Positivist and Interpretivist Approaches

Although there are debates between positivist and interpretivist approaches in the literature, each of them makes contribution to scientific research process (Tadajewski, 2006; Cova and Elliott, 2008). Major criticisms to positivist approach are; since positivism depends on generalistic approach, this leads to the problem of induction, and although positivism is depending on objectivity , observations are value-laden, theory-laden and interpreted (Anderson, 1983; Hudson and Ozanne, 1998). On the other hand, major criticisms that are directed to interpretivistic approach are; an individual cannot experience the thoughts of another individual and there might be biases in the researcher and the informant (Hudson and Ozanne, 1998). Bryman and Bell (2007) asserted that; positivist/interpretivist distinction arose as a result fundamental differences between natural and social sciences. Holbrook and O’Shaughnessy (1988) asserted that; research process needs an interpretive perspective in social sciences, a positivistic perspective in natural sciences.

3. Methodologies in Scientific Research Process

In this part, different methodological approaches in the literature are presented. Sobh and Perry (2005) and Guba and Lincoln (1994) divided research paradigms into three; ontology, epistemology and methodology. According to Sobh and Perry (2005, p.1194) ‘Ontology is reality, epistemology is the relationship between that reality and the researcher, and methodology is the techniques used by the researcher to discover that reality’. Among these paradigms; Deshpande (1983) evaluated methodology as the fundamental distinction between these paradigms and divided methodological approaches into two; qualitative methods which are developed for ‘discovering or generating theories’ and quantitative methods which are developed for ‘verifying and confirming theories’.

As mentioned in the previous part, quantitative methodology is generally related to positivistic approach which is mostly applied to a natural science (Deshpande, 1983). It depends on empirical research and independent investigator and investigated, in other words, investigator investigates the phenomena without influencing on it (Guba and Lincoln, 1994). In a quantitative research, causality between the variables is the major aim where larger sample sizes and statistical methods are used (Denzin and Lincoln, 1994). Lastly, it can be evaluated as a deductive, objective and outcome-oriented method (Deshpande, 1983)

On the other hand, quantitative methodology is generally related to interpretivist approach which is mostly applied to a social science (Altheide and Johnson, 1994). In this type of research, there is an interaction between the investigator and the investigated, so investigator has an influence on the findings (Guba and Lincoln, 1994). Moreover, since reality is not independent from individuals’ minds, there are multiple subjective realities located in a qualitative method. Finally, this method can be evaluated as an inductive, subjective and process-oriented method (Deshpande, 1983).

According to Levy (2005), growth of qualitative methods resulted with resistance by the people who rely on quantitative methods and are threatened by qualitative techniques will replace quantitative ones.

In addition to qualitative and quantitative methodologies, since Campbell and Fiskel’s   (1959) multiple operationism, a lot of researchers rely on more than one technique. This combination of methodologies is defined as triangulation (Denzin, 1978). According to Pawson and Tilley (1997) triangulation provides a “family of answers”.

Following parts of the study will deal with nature and scope of marketing, and philosophical debates in marketing’s literature in order to decide general philosophical perspective and methodology of marketing research

4. The Nature and Scope of Marketing

In the previous parts, philosophical perspectives and methodologies in scientific research process were presented. In this part of the study, nature and scope of marketing will be presented in order to determine philosophical foundations of marketing research at the end of the study.

Definition of marketing has been evolving until today like marketing itself. Since 1935 American Marketing Association (AMA) has launched 4 different definitions of marketing (AMA definition is worldwide accepted definition that is used in books, articles and other publishings.)

AMA definition in 1935

‘Marketing is the performance of business activities that direct the flow of goods and services from producers to consumers.’

AMA definition in 1985

‘Marketing is the process of planning and executing the conception, pricing, promotion, and distribution of ideas, goods and services to create exchanges that satisfy individual and organizational objectives.’

AMA definition in 2004

‘Marketing is an organizational function and a set of processes for creating, communicating, and delivering value to customers and for managing customer relationships in ways that benefit the organization and its stakeholders.’

AMA definition in 2007

‘Marketing is the activity, set of institutions, and processes for creating, communicating, delivering, and exchanging offerings that have value for customers, clients, partners, and society at large.’

According to these definitions, it can be told that; nature and scope of marketing has been broadened day by day.

  • In the first definition that was made in 1935, marketing was defined as just an exchange process between buyer and seller.
  • Definition that was made in 1985 divided buyer into 2 as organizational and individual, also mentioned about different tools like concept, price, promotion and distribution that seller can use for marketing its goods and services. (These 4 fundamental concepts of marketing were firstly being asserted by McCarthy in 1960 under the name of ‘Marketing 4P’s and became one of the most cited thought regarding to scope of marketing)
  • In 2004 AMA mentioned about marketing as a mutual benefit process between marketer and customer that starts by creating a value and ends with delivering this value to the customers.
  • Lastly in the latest definition, AMA broadened the concept of marketing and defined marketing as a process that affected the society as a whole.

Despite AMA definitions, different definitions were made by marketers according to different approaches;

Economics approach: Marketing includes all business activities that involved in the process from the hands of producers to the hands of final customers. (McNair et al. 1975).

Consumer’s (or buyer’s) approach: Star et. al. (1977) defined marketing as a process of an organization which includes selecting targeting customers, assessing their needs and managing organization’s resources to satisfy these customers’ needs.

Finally, as a managerial approach;

Societal approach: Mazur dealt with marketing’s societal side and defined it as the delivery of a standard of living to society (1947).

Managerial approach: Eldridge (1970) defined marketing as combination of activities to produce profit by investigating, creating, stimulating, and satisfying the needs of a detected segment in the market.

If all these different definitions from different perspectives are analyzed;

  • Economics approach mentions about the core subject of marketing which is ‘exchange’
  • Consumer’s approach is about the needs, wants, perceptions, attitudes and other related psychological factors about human beings.
  • Societal approach deals with relationships of human beings with each other and with the society.
  • Managerial approach concentrates the process of constructing a marketing plan which is supported by qualitative and quantitative research methods.

To sum up, it can be told that marketing is a social science which deals with the exchange that occurs between buyer and seller by employing puzzle solving progressive qualitative and quantitative methods. It is also interrelated with other social sciences

5. Philosophical Debates in Marketing

In this part of the study, philosophical debates in marketing literature are presented. Up until know, marketing academicians have chosen different guiding epistemological and ontological philosophies while they were asserting their ideas about the theoretical foundations of marketing. Different academicians reached the same answer that marketing is a science or marketing is not a science by using different approaches, in other words, although they reached the same destination they had used different vehicles and different routes. When the literature is reviewed; from all of different thoughts about philosophical foundation of marketing science, a debate between two leading philosophical approaches came forward: logical empiricism and relativism.

Logical empiricism was firstly mentioned by Hunt (1983) and for most of academicians it is still the leading philosophical paradigm that dominates academic marketing inquiry.

During 1920s positivism emerged as a philosophy of science in the form of logical positivism (Anderson, 1983). Moritz Schlick led the logical positivism stream (established by a ‘Vienna Circle’ – a group of scientists and philosophers-) and evaluated this approach as the central doctrine for Wittgenstein’s verification theory of meaning (Brown, 1977; Howard and Sheth, 1969; Passmore, 1967). According to verification theory, scientific and non-scientific statements can be differentiated if these statements can be empirically verified or not. Logical positivists believed that universal scientific propositions are true whether they have been verified by empirical tests, since Hume’s ‘problem of induction’ claims that; no finite number of empirical tests can ever guarantee the truth of universal statements (Anderson, 1983; Black, 1967; Brown, 1977; Chalmers, 1976; Hume, 1911). This difficulty was interpreted by Hempel (1965) as ‘inductive inference can never be justified on purely logical grounds’ (Anderson, 1983)

Because of these difficulties, a new version of positivism that is known as ‘logical empiricism’ was being developed by Carnap (1936, 1937). This new type of positivism became the ‘received view’ in philosophy of science for 20 years (Suppe, 1974) and it is still dominated the debates about scientific method in marketing (Hunt, 1973). By putting forward logical empiricism; Carnap tried to replace the concept of verification with confirmation because he believed that no theory can ever be ‘verified’ but they all can be ‘confirmed’ by a number of empirical tests. Figure 2 represents logical empiricist model of scientific method (Zaltman et al., 1973)

According to Anderson, (1983, p. 19), as it is illustrated in the figure; according to logical empiricists, ‘scientific process begins with the untainted observation of reality and this provides the researcher with his/her image of real world structure from which he/she cognitively generates an a priori model of the process to be investigated. Hypotheses are derived from the model and are subjected to the empirical tests. If the data are in accord with the hypotheses, a confirming instance has been identified. Thus, science progress through the accumulation of multiple confirming instances obtained under a wide variety of circumstances and conditions’ and he added that statistical inductive method is used by logical empiricists and by this method science begins with observation and moves along with further observations that are applied for justifying its theories by the help of probabilistic supports.

In his article Anderson described the logical empirical approach and presented its steps like the figure above. However, Anderson concluded in his article as relativism should be the philosophical ground for marketing science in contrast to positivism and logical empiricism. From that moment, a group of academicians led by Paul Anderson started to argue that marketing theories should be judged by relativistic criteria (Sheth et al., 1988).

According to Anderson (1983) first of all, theory justification that is dependent on positivism cannot be maintained as a viable description and secondly, there is not a consensus on the nature or existence of a unique scientific method and there is not a demarcation between science and pseudo-science. For these reasons, he claimed that; instead of asking what is the ‘correct’ method, methodologies that will convince the marketing community of the validity of a particular theory should be asked. That’s why, he believed that relativistic approach can be the only viable solution to the problem of scientific method because relativism implies that there are few truly universal standards of scientific adequacy and because of that reason different disciplines use different methodologies.

Anderson’s ideas are supported by different academicians. By expanding ideas that were generated by Thomas Kuhn and Paul Feyerabend, Peter and Olsen (1983) put forward relativism as the proper philosophical domain of marketing science because of their following claims;

  • There is a interaction between researchers which influences each other
  • Each individual researcher has his/her own beliefs and value
  • Like observational data that are used in research process, subjective interpretations of the researcher also important when conduction a research.

Muncy and Fisk (1987) also asserted that ‘truth’ or ‘evaluation of truth’ can be changed between individuals or different situations.

6. Philosophical Foundations in Marketing Research

In this part of the study, ideas about different philosophical perspectives in a scientific research process that is presented in the first part of study and different methodological approaches that is presented in the second part of the study, will be evaluated with nature and scope of marketing that is presented in the third part of the study, and philosophical debates in marketing literature that is presented in the fourth part of the study. These evaluations are made in order to determine general philosophical perspective and dominating methodological approach in marketing research.

In the first part, two dominating paradigms which are positivism and interpretivism were analyzed. In positivistic approach, research process is defined as a generalistic quantitative approach which aims explanation, gives importance to causality and contains single, objective reality that is independent of researcher. In contrast, in interpretivistic approach, research process is defined as a particularistic qualitative approach which aims understanding, gives importance to simultaneous shaping and contains multiple, social constructed, subjective reality that is dependent on researcher. Since scope of marketing is defined as a social process, according to this discrimination and Holbrook and O’Shaughnessy’s proposal (1988) which claims that research process needs an interpretive perspective in social sciences, it seems like marketing research process is closer to interpretivistic approach. However, if philosophical debates in marketing literature are examined, it is discovered that; there are two leading philosophical approaches which are logical empiricism and relativism. The arguments and assumptions of logical empiricists are closely related to positivists where the arguments and assumptions of relativist are closely related to interpretivists. These results show that, although scope of marketing is closer to the interpretivist approach, existence of different philosophical approaches in marketing literature shows that in marketing research process there is not a single general philosophical perspective. This finding corresponds with Deshpande’s (1983) approach which claims that; perspective of a marketing researcher changes according to type of research. If the research is for theory construction, qualitative (interpretivistic) approach, if it is for theory testing, quantitative (positivistic) approach would be appropriate.

In the second part of the study, two methodological approaches are presented which are qualitative and quantitative methodologies. Quantitative methodology is defined as a deductive, objective and outcome-oriented positivistic methodology that depends on empirical research and is conducted by an independent investigator aiming to detect the causality between the variables. On the other hand, quantitative methodology is defined as an inductive, subjective and process-oriented interpretivist methodology that is conducted by participant investigator. Since marketing is defined as a social science which deals with the exchange that occurs between buyer and seller by employing puzzle solving progressive qualitative and quantitative methods, marketing research process can be classified as a mixed approach research process according to scope of marketing. This is strengthened by philosophical foundations in marketing literature; in both logical empiricist and relativist approaches in the marketing literature, sometimes qualitative, sometimes quantitative and sometimes both methodologies are used.

7. Conclusion

In this study, different philosophical perspectives and different methodological approaches in scientific research process are analyzed. Ideas derived from these analyses are compared with the nature and philosophical foundation of marketing in order to detect philosophical foundations of marketing research. After comparison, two results are obtained.

Firstly, there is not a unique philosophical scientific approach in marketing research process and it depends on the type of research that is conducted by the marketing scientist. If the research is conducted in order to construct a new theory, at this time, this research might be conducted in an interpretivistic approach. On the other hand, if the research is conducted in order to test an existing theory, at this time, this research might be conducted in a positivistic approach.

Secondly, just like philosophical perspective, there is not a unique methodological approach in marketing research process and it depends on the type of research that is conducted by the marketing scientist. Appropriate methodology for a research process in marketing depends on the purpose of the research conducted. If the researcher is aiming to conduct an exploratory research, at this time a qualitative research would be more appropriate. On the other hand, if researcher’s aim is conducting a confirmatory research, at this time a quantitative research would be more appropriate.

As a conclusion, although different sides are taken in the literature regarding general philosophical perspective and methodological approaches in scientific research process, when marketing is the issue; because of the nature and philosophical foundations of marketing, general philosophical perspective and methodological approach of marketing research varies according to the aim and scope of the research. In the literature studies in different perspectives and methodologies can be found. All in a word, philosophical foundation of a marketing research is shaped by this research itself, that’s why, there is not a unique philosophical perspective or methodological approach when marketing research process is the issue.

Author: Z. Eren Kocyigit | 2013

For these kinds of digital marketing resources click and sign up for marketing newsletter or follow on feedly or check these blog posts


Z. Eren Kocyigit

Website | Twitter | Newsletter



Cova, B. & Elliott, R. (2008) Everything you always wanted to know about interpretive consumer research but were afraid to ask. Qualitative Market Research: An International Journal, 11 (2), , 121-129.

Shankar, A. and Goulding G. (2001), “Interpretive consumer research: two more contributions to theory and practice’’, Qualitative Market Research: An International Journal, Vol. 4, pp. 7-16.

Holbrook, Morris B. and John O’Shaughnessy (1988), “On the Scientific Status of Consumer Research and the Need for an Inter pretive Approach in Studying Consumer Behavior,” Journal of Consumer Research, 15 (December), 398-402.

Guba, E. G., & Lincoln, Y. S. (1994). Competing paradigms in qualitative research. In N. K. Denzin & Y. S. Lincoln (Eds.), Handbook of qualitative research (pp. 105-117). Thousand Oaks, CA: Sage.

Levy, S.J. (2005) ‘The Evolution of Qualitative Research in Consumer Behavior’, Journal of Business Research 58(3): 341–7.

Hudson, Laurel Anderson and Julie L. Ozanne (1988), “Al- ternative Ways of Seeking Knowledge in Consumer Re-

search,” Journal of Consumer Research, 14 (March), 508-521

Sobh, R & Perry, C 2005, ‘Research design and data analysis in realism research’, European Journal of Marketing, vol. 40, no. 11/12, pp. 1194-1209

Deshpande, R. (1983), “‘Paradigms lost’: on theory and method in research in marketing”, Journal of Marketing, Vol. 47, pp. 101-10.

Becker, J. and Niehaves, B. 2007, “Epistemological Perspectives on IS Research – A Framework for Analysing and Systematising Epistemological Assumptions,” Information Systems Journal (17:2) pp 197-214.

Burrell, G. & Morgan, G. (1979) Sociological Paradigms and Organizational Analysis. Heinemann, London, UK.

Morgan, Gareth, and L. Smircich, (1980), “The Case for Qualitative Research,” Acad. Management Rev., 5 491-500.

Rubinstein, D. (1981). Marxand Wittgenstein.~Socialpraxis and social explanation. London: Routledge& Kegan Paul.

Wax, Murray L. 1967. On Misunderstading Verstehen. A Reply to Abel. Sociology and Social Research. Vol. 51. April. pp. 323-333

K. Denzin, The Research Art in Sociology: A Theoretical Introduction to Sociological Methods, Butterworths, London (1970).

Mazur, P. (1947) ‘Does distribution cost enough?’, Fortune 36 (November), p. 138.

Hunt, S. D. (1976a). ‘The Nature and Scope of Marketing’. Journal of Marketing, 40, 17-28.

Hunt, S.D. (1976b), Marketing theory, Columbus, OH: Grid

Hunt, S.D. (1983), Marketing theory, Homewood, IL: Irwin

Hutchinson, K.D. (1952). ‘Marketing as a science: An appraisal.’ Journal of Marketing, 16(3), 286-293.

Howard J.A and Sheth J.N (1969), The Theory of Buyer Behavior, New York: John Wiley and Sons.9-28

Eldridge, C. E. (1970) Marketing for Profit,London: Macmillan.

Buzzell, R.D. (1963). ‘Is marketing a science?’, Harvard Business Review, 41(1), 32-48.

Campbell, N. (1952), What is Science?, Dover, U.S.A.

Anderson, P.F. (1983), ‘Marketing, Scientific Progress, and Scientific Method’, Journal of Marketing, 47, (Fall), 18-31

Zaltman, Gerard, Christian R.A. Pinson and Reinhard Angelmar (1973). Metatheory and consumer research. Chicago. III: Dryden Press.

McNair, M. P., Brown, M. P., Leighton, D. S. R. And England, W. B. (1957) Problems in Marketing, 2nd edn, New York: McGraw-Hill.

Star, S. H., Davis, N. J., Lovelock, C. H. and Shapiro, B. P. (1977) Problems in Marketing, New York: McGraw-Hill.

Campbell and J. Stanley,1963, Experimental and Quasi-Experimental Designs for Research.Rand McNally College Publishing,

Kerlinger, F. N. 1986. Foundations of Behavioral Research, 3rd ed. Holt, Rinehart and Winston, New York.

Denzin, N. K. & Lincoln, Y. S. (1994). Introduction: Entering the field of qualitative research. In: N.

Denzin & Y. S. Lincoln (eds.), Handbook of Qualitative Research. Thousand Oaks, CA: Sage, 1–17.

Altheide, D. L. & Johnson, J. M. (1994). Criteria for assessing interpretive validity in qualitative research. In: Denzin, N. K. & Lincoln, Y. S. (eds), Handbook of Qualitative Research. Thousand Oaks, CA: Sage Publications, pp. 485–499 Bryman, A. and Bell, E 2007)Business Research Methods , Second Edition, Oxford: OxfordUniversity Press