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Combining quantitative and qualitative approaches
Tallinn Pedagogical University
Narva mnt 25, Tallinn, 10120, ESTONIA
Last year in Lahti I gave a paper concerning the debates (sometimes called as "paradigm wars") about differences and similarities between quantitative and qualitative research. I also presented the results of my small-scale investigation, which showed that there were studies, which combined qualitative and quantitative approaches in different ways. In this paper I want to look further and address some problems concerning the use and integration of multiple methods in a social scientific study.
In a long run there are three different widely advocated positions towards the possibility and usefulness to use quantitative and qualitative approaches in complimentary, combined or mixed ways:
The advocates of the first position, which I would call strong paradigmatic view, declare that only one of those approaches is good/appropriate/scientific enough for the inquiry about the social life. They say that quantitative and qualitative research methodologies are tightly bound to different mutually exclusive epistemological positions. From here follows that there is no point even to talk about the possibility of combining or mixing of those approaches. The proponents of this position are sometimes called purists.
The advocates of the second position, which I would call week paradigmatic view, are somewhat more tolerant towards different methodologies saying that both of them can be used and are useful, but as they carry with them different philosophical underpinnings they are suitable in very different situations and contexts and therefore one can not and should not mix or combine quantitative and qualitative approaches in the framework of one study. The proponents of this view are sometimes called situationalists.
The advocates of the third position regard quantitative and qualitative approaches both as useful and proper ways of going to study the social world. Although they see some major differences between quantitative and qualitative research they also see some important similarities between them and advocate the integrated use of different methodologies if this can advance our understanding about the phenomenon under the investigation. The proponents of this position are sometimes called pragmatists.
All of these three positions bring up some skeptical questions and problems one needs to address and solve. In this paper I will take the pragmatist position, which means that I will not question the feasibility of combining quantitative and qualitative ways of doing research in general. I rather
try to look more closely on problems, which we have to be aware of in the process of doing so.
Thus, I will not discuss problems, which paradigmatic view brings with it as this subject has been the focus of many previous papers (including mine from the last conference in Lahti).
Calls for multimethod approach.
Although the calls for the use of multiple methods in the framework of one study are maybe even older than the quantitative-qualitative debate, the area of 'how, when and why different methods might be combined' has got much less attention than the philosophical aspects of paradigmatic view (Bryman 1988, 155). One can not say that there is a complete lack of literature concerning different aspects of combining divergent methodologies. Still most of the literature, which classifies under the broad area of combining qualitative and quantitative approaches, are arguments why this integration is possible and needed. On the other hand there is a considerable number of papers either describing authors' own experiences on integrating some aspects of quantitative and qualitative methodologies or following so called 'case law' approach where a number of different experiences are assembled together and called upon as exemplars one could follow (see for example Brannen 1992, Brown et al. 1996, Bryman 1988, Caracelli & Greene 1993, Carey 1993, Maxwell et al. 1986).
As an example of the early call for leaving our methodological preconceptions behind us and for considering all possible ways for advancing our knowledge about the important aspects of social life I would like to quote Trow's paper where he suggested that we, researchers in social sciences, should:
Approximately as early Donald Campbell and his co-authors published several papers where they advocated the use of multitrait-multimethod matrixes and triangulation of measurement for validation, proposed 'transition experiments' and quasi-experimental designs (see Campbell 1957, Campbell & Fiske 1959, Campbell & Stanley 1963, Webb et al. 1966). Although remaining in the framework of quantitative tradition we can see in these early works the attempt to advocate the use of multiple methods as well as the possibility to mix some aspects of quantitative and qualitative methodologies.
Drawing on these ideas Denzin (1978) developed the concept of triangulation - the term that is probably most widely used to denote any attempt to combine or mix different methods in a research study. As it often happens, the most widely used terms tend to be the most overused and abused terms as well, and 'triangulation' is not an exception here I think. One could draw obvious parallels in how the term's 'paradigm' and 'triangulation' have lost their initial quite narrow and well-defined meaning and became to denote something general and indefinite.
However, by Denzin triangulation means more than using multiple measurements of the same phenomenon - in addition to the use of diverse data, it involves combining different methods and theories, as well as perspectives of different investigators. Denzin (1978) has clearly identified four different types of triangulation:
data triangulation- the use of variety of data sources and data sets in a study. Data may be both qualitative and quantitative, gathered by different methods or by the same method from different sources or at different times.
investigator triangulation- the use of several different researchers. Here the importance of partnership and teamwork is underlined as the way of bringing in different perspectives.
theory triangulation- the use of different theoretical viewpoints for determining competing hypotheses as well as for interpreting the single set of data.
methodological triangulation- the use of multiple methods to study a single problem or phenomenon. It may also include the use of the same method on different occasions and situations.
We can see that the concept of triangulation is based on the assumption that by using several data sources, methods and investigators one can neutralize bias inherent in one particular data source, investigator or method (Jick 1979). It is often stressed out that different methods have different weaknesses and strengths and therefore the main effect triangulation can offer is to overcome the weaknesses of any single method. Thus, if we use several different methods for investigation of the phenomenon of our interest and the results provide mutual confirmation we can be more sure that our results are valid. Within this context, quantitative and qualitative approaches are usually seen as different ways of studying the same phenomenon and able to answer the same research questions (Bryman 1988).
Although the perspective of triangulation seems to be very promising several authors have warned us about the hidden problems that the combined use of qualitative and quantitative methods for the purposes of triangulation can bring with it. Bryman (1992) has raised three alarming questions. First, as quantitative and qualitative research have different preoccupations it is highly questionable whether they are tapping the same things even when they are examining apparently similar issues. Second, if quantitative and qualitative findings do not confirm each other how should the researcher respond. And third, if the conflict in results is present what it actually means and comprises. Thus, in the context of combining qualitative and quantitative approaches the concept of triangulation is not as unproblematic as it may appear.
On the other hand in the wider framework of integrated use of qualitative and quantitative approaches the triangulation is offering quite limited possibilities. As in the case of triangulation the results of different methods are supposed to validate each other it means that different methods have to be highly independent throughout the study. This approach excludes the possibility to mix quantitative and qualitative aspects on different levels of investigation. For example one of the few books devoted entirely to the problems of combining quantitative and qualitative approaches Multimethod Research. A Synthesis of Styles by Brewer and Hunter (1989) is largely constrained by the framework of triangulation although the authors mention the other possibilities for integration as well. They classify studies into three categories: a) monomethod studies, b) composite method studies, which combine some elements of the basic monomethod styles and c) multimethod studies, which combine the basic styles of research. The authors give their clear preference to the multimethod designs because according to them composite methods 'comprise some of the basic methods' sources of sterngth' and they 'fail to provide the opportunity for triangulated measurement and hypothesis testing, and the protection against monomethod bias, that the multimethod strategy provides' (Brewer and Hunter 1989, 81).
Other rationales for combining quantitative and qualitative research
Regardless of this extensive critique of composite method designs several studies have indicated that we can find considerable number of studies which actually combine some elements of quantitative and qualitative approaches on the various stages of the study (See for example Bryman 1988, Datta 1994, Greene et al. 1989, Niglas 1999). Maybe the most interesting (although definitely not the most systematic) of theses studies is Datta's analysis of several papers given to her as examples of good qualitative and quantitative research by the proponents of monomethod approach. Her conclusion was that 'the best examples of both paradigms seem actually to be mixed models' (Datta 1994: 67). As a result of the extensive literature review and a small-scale empirical analysis of published research papers I have suggested that quantitative and qualitative approaches have been combined in various ways and various levels of the inquiry. Different possibilities for mixing quantitative and qualitative research can be illustrated by the Figure 1 (Niglas 1999). Thus, we can see that in the practice researchers mix and combine qualitative and quantitative methodologies, but the question remains if this kind of action has to be approved and what is the rationale for doing so.
Figure 1. Different levels of research in practice
There are some methodologists who propose that the combination of various elements of quantitative and qualitative approaches can offer much wider possibilities than Brewer and Hunter describe (See for example Brannen 1992, Bryman 1992, Datta 1994, Patton 1990, Cresswell 1995, Tashakkori and Teddlie 1998). Although these authors see the potential of studies with various mixed designs, their overall concern seems to be that we still lack a comprehensive theoretical background for mixed-model designs and therefore mixed-model studies can seem to many practitioners, consumers and evaluators of the research as 'mixed-up models' one can not rely on (Datta 1994, 59).
There have been several attempts to clarify the issue and develop taxonomies for classification of studies combining quantitative and qualitative approaches. For example Mark and Shotland (1987) introduce in addition to triangulation two other ways of combining methods to enhance an investigation. They describe the bracketing model, which says that we should consider the results of different methods as alternative estimates. Thus, by using methods that are biased in opposite directions the true value can be bracketed. The third model they describe is complementary multiplism. Here diverse methods play complementary roles and offer different viewpoints; together, they provide evidence that is markedly strengthened.
In one of the most important books on the field Bryman (1988) described in addition to triangulation ten other ways in which quantitative and qualitative research have been combined in the research practice. Although it is a quite long list Bryman conceded that very likely it is not exhaustive (See Table 1). Drawing on the results of extensive literature review Greene, Caracelli and Graham (1989) developed a system consisting of five different mixed-method purposes. The results of their empirical study proved this taxonomy to be exhaustive as it was possible to match all mixed-method studies, they looked at, to one or more of these five purposes. I have tried to compare these two lists of purposes for mixed-method studies in Table 1. We can see that there are some remarkable similarities: in addition to triangulation the common purposes seem to be development and expansion. In the former case the results from qualitative research help to inform the use of quantitative research or vice versa and in the latter the quantitative and qualitative approaches are used sequentially on different stages of the study. It is not so easy to draw parallels between other categories as many of Bryman's ways of integration can serve diverse purposes from complementarity through initiation to expansion.
Table 1: Purposes for combining quantitative and qualitative approaches
|- seeking convergence of results from different methods.|
|- clarification, illustration, interpretation of the results from one method with the results from the other|
In regard to the previous discussion about mixing various elements of quantitative and qualitative research it is interesting to notice that the classification given by Greene et al. does not distinguish studies with mixed design elements form other methodological mixes. Nevertheless in their study the authors use some other variables which allow to speculate that some of the papers studied belonged to the former class. On the other hand Bryman has defined separate category for studies which have design elements of both research traditions. This category remains relatively weakly described by the author, although in his later work he discusses some aspects of these 'hybrid' designs (Bryman 1992).
Taxonomies for studies combining quantitative and qualitative approach.
Looking for further references to mixed designs we can see that as early as 1980 Patton added a chapter on 'methodological mixes' to his widely used textbook about qualitative evaluation methods. While also accepting the importance of triangulation he wrote that the second way of 'achieving methodological heterogeneity ... is to borrow and combine parts from pure methodological strategies, thus creating mixed methodological strategies' (Patton 1980, 109, italics added). Similarly Cresswell describes in his textbook three different designs for combined use of quantitative and qualitative research: two-phase design, dominant-less dominant design and mixed-methodology design, where the researcher 'would mix aspects of qualitative and quantitative paradigm at all or many methodological steps in the design' (Cresswell 1995, 178).
What we can learn from these different sources is that, as on any developing area, there is a lack of terminological and even conceptual clarity and coherence: we can find many different labels for the same ideas; at the same time authors use same terms in different meanings (See Table 2)., Recently Abbas Tashakkori and Charles Teddlie (1998) have made an attempt to develop exhaustive taxonomies for studies combining quantitative and qualitative approaches in different ways. They have not chosen to proceed from different purposes that combination of different methods can serve but from the way in which different methods are used/combined in a particular study. Similarly to Brewer and Hunter (1989) they divide all studies into three main types: monomethod studies, mixed method studies, and mixed model studies. Each of these basic types of studies is further divided into subcategories.The basic types are defined as follows:
Monomethod studiesfollow in all stages of the inquiry 'one of the predominant paradigms' (Tashakkori & Teddlie 1998: 17). Thus, they are either purely quantitative or purely qualitative studies.
Mixed method studiescombine the quantitative and qualitative approaches in a single study or multiphased study. Here quantitative and qualitative approaches seem regarded relatively independent, as the authors stress that all mixed method designs use triangulation techniques.
Mixed model studies'combine the qualitative and quantitative approaches within different phases of the research process' (Op sit: 19). Here qualitative and quantitative methodologies can be interwoven in different ways. They can be present as the single application on different stages of the study or they may be used simultaneously in integrated manner on the same pahse(s) of the inquiry.
In the Table 2 I have tried to compare classifications of studies that different authors have proposed. Studying their definitions of given categories it becomes clear that in spite of different labels there are considerable similarities between classifications. Although there is no one-to-one correspondents it seems feasible to organize classifications into three columns so that categories in each column are conceptually close to each other. Thus, I think that the broad classification of studies into three categories is useful and that definitions given by Tashakkori and Teddlie (1998) are conceptually reasonable. What seems to me a little questionable is their choice of labels for these categories. First, the use of the term 'mixed' for the second category gives a somewhat different depiction as the definition itself. It was made quite clear that in this category while combined in one study the quantitative and qualitative approaches remain relatively independent at least until the interpretation phase. The word 'mix' on the other hand usually carries an opposite notion. For example the first meaning that The Oxford Dictionary of Current English gives for the term 'mix' is:
Therefore it seems to me that the use of the word 'multi' or 'multiple' would be more appropriate for this category.
The second problematic word is 'method' as in my view it is more often connected with concrete techniques for data gathering and data analysis than with the whole set of methodological issues. Therefore the label 'monomethod studies' sounds too restrictive, as studies in the first category can exploit in the framework of one methodological approach (either quantitative or qualitative) several data sources and data gathering instruments. But it is not so easy to replace that term as conceptually better terms are considerably longer and inconvenient to use. Therefore, in the following, I will continue to use the term 'method' in its wider sense, comprising all stages of the research.
Finally, as both terms 'multimethod' and 'mixed-method' have been used as an umbrella-terms for all possible designs, where any combination of quantitative and qualitative approaches occurs, the more restricted use of these terms may be confusing, but I could not find a way to substitute them. Thus, in the first row of Table 2 I have given labels and short definitions for the three broad categories of research designs.
Table 2: Proposed classifications of studies by their ways of using/combining quantitative and qualitative approaches
purely quantitative or purely qualitative designs (may involve the use of several data sources and/or data gathering instruments from the same approach).
designs where both quantitative and qualitative approaches are used, but they remain relatively independent until the interpretation stage.
designs where elements of quantitative and qualitative approach are combined in various ways within different phases of the study.
For better and more detailed descriptions of different possibilities of combining quantitative and qualitative approaches this broad classification needs to be divided into subcategories. For the first two categories this can be done quite easily, as there are several methodological texts concerning the issue and we can see considerable agreement between different authors. There are two important dimensions, which can be the basis for the classification: timing and the importance given to divergent methods in the study. If different methods are used independently on different phases of the inquiry then we can talk about sequential design; if they are used in a parallel way at the same time we can talk about parallel/simultaneous design. Similarly, if different approaches are given approximately the same weight in the study we can talk about equivalent status design and if one method is clearly prevailing we can talk about dominant-less dominant design. By combining these possibilities for the studies either using several different methods within the same approach or for studies using both quantitative and qualitative approaches we will get six subgroups for pure designs and eight subgroups for multimethod designs (For full list of these subcategories see Tashakkori & Teddlie 1998: 15).
The further classification of studies with mixed design is considerably more complicated, as there are many different ways one can mix quantitative and qualitative approaches within the framework of one study. As here the elements of divergent approaches can occur on different phases of the inquiry it is essential for any classification that we divide the empirical study into methodological stages. It is common to include in methodological textbooks figures or tables describing basic steps of the research process. For my own teaching purposes I have developed the model given on the Figure 2. For the present discussion it is important to notice that in my view decisions made on earlier steps influence the decisions one can take on the later steps but there is no one-to-one relationship between methods available on different stages. This means that there is a possibility to combine quantitative and qualitative elements on any of described stages of the research.
Figure 2. Methodological decisions to be made and steps to be taken in the process of the empirical research study:
However, for the purposes of classification of studies with mixed designs less detailed division may be more suitable, as the combination of six or even more levels will produce too many subgroups. In their inquiry of mixed-method studies Greene et al. (1989) identified two broad levels of methodology: paradigms and methods, where method refers to data gathering and handling techniques and paradigm refers to the wider set of methodological and philosophical ideas. Patton (1980) operated with three levels and divided possibilities at all levels into two basic types, one of them regarded as qualitative and the other as quantitative: design (experimental v naturalistic), measurement (quantitative v qualitative) and analysis (statistical v content/qualitative). By combining these two different possibilities at all three levels he got two pure strategies and four mixed forms:
Mixed form I: QUAN QUAL QUAL
experimental design, qualitative measurement, content (qualitative) analysis
Mixed form II: QUAN QUAL QUAN
experimental design, qualitative measurement, and statistical analysis
Mixed form III: QUAL QUAL QUAN
naturalistic inquiry, qualitative measurement, statistical analysis
Mixed form IV: QUAL QUAN QUAN
naturalistic inquiry, quantitative measurement, statistical analysis
Tashakkori and Teddlie (1998) took over Patton's three-dimensional model proposing some terminological changes and essential extensions. They gave following labels to the three levels of research study: 1) type of inquiry (exploratory investigations and confirmatory investigations), 2) data collection and operations (qualitative and quantitative), 3) data analysis and inference (qualitative and statistical). To get an exhaustive taxonomy Tashakkori and Teddlie added two 'rare' mixed forms to their classification, which Patton (1980) had excluded:
Mixed form V: QUAN QUAN QUAL
confirmatory investigation, quantitative data/operations, qualitative analysis/inference
Mixed form VI: QUAL QUAN QUAL
exploratory investigation, quantitative data/operations, qualitative analysis/inference
In addition to these six mixed types where on every stage of the study there is used only single approach Tashakkori and Teddlie gave examples of studies with more complex mixed designs where both quantitative and qualitative approach are used one the same stage of the inquiry.
The authors claim that proposed three expanded dimensions with relevant categories are representative of basic steps one has to take in the course of the research study. However, by studying their definitions I see an important gap in these dimensions. The first dimension type of investigation is based on the 'distinction between studies with a priori hypotheses (confirmatory investigation) and those without a priori hypotheses (exploratory investigations)' (Tashakkori & Teddlie 1998: 53). The second dimension data collection and operations concerns in the first place 'the form of data', but it also includes the measurement techniques, methods for establishing the reliability and validity of result as well as sampling procedures (op sit: 54). My main concern here is that they exclude the overall design or strategy from their dimensions or put it implicitly into the same dimension with data collection techniques. I even tend to object the idea that sampling should be in the same group with data collection techniques, as the results of my small-scale study showed that there were studies with qualitative design and sampling, which used mainly quantitative data collection techniques (Niglas 1999). Thus, I propose that overall design and sampling techniques should form the separate dimension between the type of the study and the data collection. If we look at Patton's original classification we see that his first dimension comprises the overall design of the study, but the weakness of his classification is that the given categories: naturalistic inquiry versus experimental design are too restrictive, excluding many design options there are available.
In this paper I have given a short overview of the evolution of ideas how quantitative and qualitative approaches can be combined in the social research to advance our knowledge about important aspects of our life. We have seen that the idea to use multiple methods in the framework of one study was proposed already in the middle of the past century by influential methodologists like Campbell, Stanley and others. Soon the idea was taken further suggesting that the combination of quantitative and qualitative research, which were by many methodologists seen as incommensurable opposites, is not only feasible and beneficial in solving our puzzles, but can solve some problems the 'pure designs' can not overcome. Relying mainly on the examples from the research practice different authors have listed various reasons for combination of quantitative and qualitative aspects in a single study. More recently the attempts to chart the area by developing taxonomies for studies combining quantitative and qualitative research in different ways have been made. In this paper I have described several possibilities of this classification proposed by different authors and pointed to some problems related to the definition of dimensions which could be the basis for classification of mixed designs.
In this short review article it has not been possible to focus on full list of important issues related with possibilities and ways of combining quantitative and qualitative research. In spite of their rejection of the incompatibility thesis several authors have pointed to important problems one has to be aware of and deal with while combining different elements of quantitative and qualitative approaches (See for example Bryman 1992). Further, there are strong arguments that it is oversimplified and even wrong to talk about two clearly distinguishable approaches as the differences within quantitative and qualitative approaches are not smaller or less important than between these two categories (Hammersley 1995 a). On the one hand this argument supports the idea that indeed we can and we do combine or mix design elements usually connected with divergent approaches, but on the other hand it questions the basis for taxonomies of mixed designs as whatever dimensions we take it is not possible to define two clearly separate categories: quantitative and qualitative. As an example I would mention the confusion about the methods of manifest content analysis, which have been seen by some authors as quantitative and by others as qualitative data analysis techniques.
In summary it has to be said that although some aspects of combined use of quantitative and qualitative approaches have been studied in more detail (see for example the work on data analysis strategies for mixed-method studies by Caracelli and Greene (1993)), there is a need for further research to clarify the implications of various mixed designs to the research results.
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