Combining Qualitative and Quantitative Sampling, Data ... Qualitative and Quantitative Sampling, ... arguably the key difference between “quali- ... While qualitative research typically involves pur-

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  • Research in Nursing & Health, 2000, 23, 246255

    246 2000 John Wiley & Sons, Inc.

    Focus on Research MethodsCombining Qualitative

    and Quantitative Sampling,Data Collection,

    and Analysis Techniques in Mixed-Method Studies

    Margarete Sandelowski*

    University of North Carolina at Chapel Hill, School of Nursing, 7460 Carrington Hall, Chapel Hill, NC 27599

    Received 12 July 1999; accepted 13 January 2000

    Abstract: Researchers have increasingly turned to mixed-method techniques to expand thescope and improve the analytic power of their studies. Yet there is still relatively little direction onand much confusion about how to combine qualitative and quantitative techniques. These tech-niques are neither paradigm- nor method-linked; researchers orientations to inquiry and theirmethodological commitments will influence how they use them. Examples of sampling combina-tions include criterion sampling from instrument scores, random purposeful sampling, and strat-ified purposeful sampling. Examples of data collection combinations include the use of instru-ments for fuller qualitative description, for validation, as guides for purposeful sampling, and aselicitation devices in interviews. Examples of data analysis combinations include interpretivelylinking qualitative and quantitative data sets and the transformation processes of qualitizing andquantitizing. 2000 John Wiley & Sons, Inc. Res Nurs & Health 23:246255, 2000

    Keywords: mixed-method studies; combination studies; qualitative and quantitative research; sampling; data collection; data analysis; triangulation

    The idea of mixing qualitative and quantitativemethods has stimulated much interest and debate(e.g., Greene & Caracelli, 1997a; Sandelowski,1995; Swanson, 1992; Tashakkori & Teddlie,1998). Researchers increasingly have used mixed-method techniques to expand the scope of, anddeepen their insights from, their studies. As advo-cates of mixed-method research have argued, thecomplexity of human phenomena mandates morecomplex research designs to capture them. De-spite this interest, there is still relatively little di-rection on and much confusion about how to ac-complish mixed-method studies. In this paper, Idiscuss the where, what, why, and especially, the

    how of studies combining qualitative and quanti-tative techniques.

    THE WHERE, WHY, AND WHAT OF COMBINATIONS

    Combination or mixed-method studies are con-cretely operationalized at the technique level, orthe shop floor, of research: that is, at the level ofsampling, data collection, and data analysis.Mixed-method studies are not mixtures of para-digms of inquiry per se, but rather paradigms are

    *Professor.

  • reflected in what techniques researchers choose tocombine, and how and why they desire to combinethem.

    At the Paradigm LevelAs many scholars (e.g., Guba & Lincoln, 1994;Heron & Reason, 1997) have variously named anddescribed them, paradigms of inquiry are world-views that signal distinctive ontological (view ofreality), epistemological (view of knowing and therelationship between knower and to-be-known),methodological (view of mode of inquiry), and ax-iological (view of what is valuable) positions. In-deed, paradigms of inquiry are best understood asviewing positions: ways, and places from which,to see. Because different paradigms, such as (neo-or post-) positivism, constructivism, critical theo-ry, and participatory inquiry, entail contradictoryviewing positions, combinations at the paradigmlevel are not true combinations, mergers, or rec-onciliations of worldviews, but rather the explicitframing of inquiry in two or more worldviews,each of which remains distinct from the other. Thatis, for example, it is not possible to combine, merge,or reconcile a view of reality as singular and ob-jective (positivist) with views of it as multiple andindividually or culturally constructed (construc-tivist), or as historically contingent (critical theo-ry). A critical theorist will frame the issues aroundhormone replacement for midlife women differ-ently from a neopositivist.1 That is, they will eachsee different things and, therefore, ask differentquestions that will, in turn, require the use of dif-ferent methods and techniques to answer them.Such a paradigm combination may be used to elic-it two or more perspectives on hormone therapy,or for the purpose of initiation (Greene, Cara-celli, & Graham, 1989, p. 259), to surface para-doxes and contradictions that surround hormonetherapy. Accordingly, two or more paradigms ofinquiry can be used to frame the same target phe-nomenon (in this case, hormone replacement).Yet, arguably, the positivist and the critical theo-rist may not really be studying the same phenom-enon, because to see a phenomenon in a certainway is to change that phenomenon. As Pearce(1971, p. 2) observed, a change of world view canchange the world viewed. Moreover, it is debat-able whether one researcher can hold two differ-ent viewing positions, albeit at different times.

    That is, it is uncertain whether a researcher canconduct a project framed first, for example, in pos-itivism and then later, in critical theory. Suchworldviews, like all strongly held belief systems,are not easily exchanged.

    As data collection and analysis techniques arenot linked to paradigms (Berman, Ford-Gilboe, &Campbell, 1998; Sandelowski 1995), both the re-searcher in a positivist viewing position and the re-searcher in a critical theory viewing position mayuse interviews and even the very same standard-ized measures to answer their questions, but theywill employ these techniques and, more important-ly, analytically treat their results differently. In-deed, arguably the key difference between quali-tative and quantitative (when these words areused to signal different inquiry paradigms or re-search traditions) researchers is in their attitude to-ward and treatment of data. Accordingly, althoughtechniques can be mixed, the resulting mix will re-veal the researchers viewing position (or, in casesof mixed-up research, the researchers futile effortto mix the research equivalent of oil and water).

    At the Method LevelCombinations at the method level can be used to ex-pand the scope of a study as researchers seek to cap-ture method-linked dimensions of a target phenom-enon (Greene et al., 1989, p. 259). As Wolfer (1993)proposed, different aspects of reality lend them-selves to different methods of inquiry. For example,the physiology of hormone replacement therapy forwomen lends itself to study via physiologic mea-sures, while the debate around the benefits and lia-bilities of hormone replacement therapy lends itselfto discourse, semiotic, and other cultural analyses.In the study I conducted with my colleagues of thetransition to parenthood of infertile couples (Sande-lowski, Holditch-Davis, & Harris, 1992), we usedgrounded theory methodology with naturalistic,ethological observation to capture different featuresof this phenomenon, including couples under-standings of their struggle to become parents andtheir interaction with their babies. Grounded theo-ry and ethological observation share a common nat-uralist imperative (that is, not to manipulate, or im-pose a priori conceptualizations on, the targetphenomenon) that make them compatible for use inone study. But grounded theory is particularly well-suited to theorizing human understandings, whileethological observation is especially well-suited totheorizing human behavior.

    Although the various dimensions of phenome-na may be method-linked in that different dimen-sions may be best captured by different methods,

    COMBINING / SANDELOWSKI 247

    1I use terms like positivist and positivism to quickly com-municate complex and admittedly controversial ideas for thepurposes of this paper, not to stereotype researchers or view-ing positions.

  • 248 RESEARCH IN NURSING & HEALTH

    methods, like paradigms, are not specificallylinked to techniques. Grounded theory may begenerated using an array of qualitative and quan-titative data collection techniques and sources.Moreover, methods are not uniformly linked toparadigms (Greene & Caracelli, 1997b). Groundedtheory may be conducted in a neopositivist or con-structivist paradigm (Annells, 1996). A neoposi-tivist researcher conducting grounded theory be-lieves in an external and objectively verifiablereality. In contrast, a constructivist conductinggrounded theory believes in multiple, experien-tially based, and socially constructed realities. Forthe neopositivist, concepts emerge or are discov-ered, as if they were there to be found. The act ofdiscovery is separate from that which is discov-ered. For the constructivist, concepts are made,fashioned, or invented from data. What construc-tivists find is what they made. For the construc-tivist, all human discovery is creation.

    At the Technique LevelThe technique level of research is the site wherecombinations actually occur and is what is mostoften referred to in discussions of mixed-methodresearch. Such combinations entail the use of sam-pling, data collection, and data analysis techniquescommonly (although not necessarily) conceivedas qualitative or quantitative. Because techniquesare tied neither to paradigms nor to methods, com-binations at the technique level permit innovativeuses of a range of techniques for a variety of pur-poses. Three purposes include (a) triangulation, toachieve or ensure corroboration of data, or con-vergent validation; (b) complementarity, to clari-fy, explain, or otherwise more fully elaborate theresults of analyses; and (c) development, to guidethe use of additional sampling, and data collectionand analysis techniques (Greene et al., 1989, p.259). The rest of this paper is devoted to illustrat-ing how such purposes can be achieved.

    THE HOW OF COMBINATIONS

    Mixed-method studies entail concrete operationsat the technique level of research by which qual-itative and quantitative techniques are used to-gether and either remain distinct design compo-nents, or are explicitly integrated (Caracelli &Greene, 1997). As shown in Figure 1, either qual-itative or quantitative approaches to sampling,data collection, and data analysis may prevail orhave equal priority in a study, and both qualitative

    and quantitative approaches may be used sequen-tially, concurrently and iteratively, or in a sand-wich pattern.

    Combining Sampling StrategiesOne of the most important features distinguishingwhat is commonly referred to as qualitative fromquantitative inquiry is the kind of sampling used.While qualitative research typically involves pur-poseful sampling to enhance understanding of theinformation-rich case (Patton, 1990), quantitativeresearch ideally involves probability sampling topermit statistical inferences to be made. Althoughpurposeful sampling is oriented toward the devel-opment of idiographic knowledgefrom gener-alizations from and about individual casesprobability sampling is oriented toward the devel-opment of nomothetic knowledge, from general-izations from samples to populations. Notwith-standing these key differences, purposeful andprobability sampling techniques can be combinedusefully.

    Criterion sampling. For example, in designtemplate 2 shown in Figure 1, in which the use ofquantitative techniques precede the use of qualita-tive techniques, research participants scores onthe instruments used to collect data in the quanti-tative portion of the study can be used to initiate acriterion sampling strategy. Criterion sampling isa kind of purposeful sampling of cases on precon-ceived criteria, such as scores on an instrument.Cases may be chosen because they typify the av-erage score; this kind of sampling may also be re-ferred to as typical case sampling. Cases may bechosen because they exemplify extreme scores;this kind of sampling may also be called extremeor deviant case sampling. (The term deviant hererefers to any departure from a specified norm.)Such cases are highly unusual. Or, cases may bechosen because they show a variable intensely, butnot extremely; this kind of sampling may also bereferred to as intensity sampling (Patton, 1990, pp.182183).

    Researchers using scores on instruments as thecriterion for purposeful sampling may wish to col-lect more data (e.g., via interviews or observa-tions) from the chosen participants for the purposeof triangulation: that is, to discern whether a typi-cal, extreme, or intense case of something on astandardized test is also a typical, extreme, or in-tense case using other data collection techniques.Or, researchers may use the criterion of scores(typical, extreme, or intense scores) for the pur-pose of complementarity: that is, to find out moreabout what makes a case typical, extreme, or in-

  • COMBINING / SANDELOWSKI 249

    tense. In the process of sampling for complemen-tarity, researchers will inevitably also obtain in-formation on convergent validity and, thereby,also achieve the purpose of triangulation. That is,in the process of obtaining fuller information onwhy persons scored as they did, they will also ob-tain information on whether persons look the sameon interview or observation as they did on thequantitative measure of a target phenomenon. Re-searchers will sample participants in scoring cate-gories until the point of informational redundan-cy; that is, until they have collected informationfrom enough cases in each scoring category to al-low them to draw conclusions about the validity ofthe result (if they are seeking convergent validity),or to elaborate on and clarify the result. Samplingon the basis of scores is an especially useful strat-egy in clinical trials of interventions to validate orclarify their effects on different participants.

    Random purposeful sampling. Another ex-ample of the combined use of probability and pur-poseful sampling is random purposeful sampling,which may also be used in design template 2 or 3.This sampling strategy is employed when there isa very large pool of potentially information-richcases and no obvious reason to choose one caseover another. For example, in a clinical trial of anintervention to reduce pain with 500 people, 300of them scored as having less pain on a standard-ized measure of pain, 150 scored as having asmuch pain as they had before the treatment, and 50scored as having more pain. These numbers aretoo large for any purposeful sampling strategy ori-ented toward the intensive study of the particularsof each case. Accordingly, cases can initially bechosen from each of these three scoring groups(the criterion for sampling here is again the scores)by assigning all the cases in each group a number

    FIGURE 1. Hybrid, combination, or mixed-method design templates.

  • from a random number table and then drawingthem in turn. Each case drawn must meet the min-imum criterion in all purposeful sampling: name-ly, that it is an information-rich case. And, only somany cases are drawn in each scoring group thatwill permit researchers to make the kinds of infer-ences they wish to make: for example, concerningconvergent validity, or fuller...

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