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0 Sampling for qualitative research

ualitative sampling can be confusing, especially if one’s knowledge regarding sampling methods originates

from a framework of statistical inference. Although not based on statistical theories, some basic sampling principles for conduct- ing qualitative research do exist. This column will describe some strategies for quantitative sam- pling. A brief overview of quan- titative sampling will provide a background with which one can contrast qualitative sampling.

QUANTITATIVE VERSUS QUALITATIVE SAMPLING

Quantitative researchers strive to collect large amounts of data using random selection methods. The rationale for this premise is drawn from inferential statistics and assumes that samples are drawn from a particular popula- tion. The larger the random sam- ple drawn from a given popula- tion, the less variation in each selected sample and the more representative of the given popu- lation.‘ Analysis performed on these data can be descriptive (eg, descriptions of the sample) or inferential (eg, an estimation of population parameters derived from the sample). Numerical data are used to describe the sample, examine relationships, and determine cause and effect relationships between variables.2

Quantitative data and findings have been criticized for being reductionistic and removed from human experience. In contrast,

qualitative methods seek to rep- resent holism and to provide contextual knowledge of the phenomenon being studied. One goal of qualitative research is to increase understanding of a phe- nomenon as opposed to general- izing data extrapolated from the sample to the population at large. Rather than having a quantitative research outcome of generalized findings, qualitative researchers have an onus of richly describing the findings so they can be trans- ferred to other situations. The qualitative researcher’s responsi- bility includes providing enough description about the context of the sample so that others may adequately judge whether the findings apply to their own situations.

UNDERSTANDING QUALITATIVE SAMPLING

A research consumer must ask whether there is enough evi- dence from one qualitative study to transfer the knowledge to another group of people with a similar experience or even to another type of phenomenon. For example, assume I read a study about middle-age college stu- dents’ experiences with test anx- iety. The researcher provided enough description and context of the sample and findings that, after reading it, I found it could apply to my 15-year-old daugh- ter when she takes tests. I also concluded the findings apply and provide insight into preoperative patient anxiety. Of course, these

are potential areas for future research; however, as an individ- ual searching for knowledge, this study provided increased under- standing of the phenomenon of anxiety.

Understanding what purpose research will serve should be a decisive factor in selecting a qualitative sample. A researcher has many sampling choices available that may stem from theory, method, or simple practi- calities, such as time and money. A sample, therefore, is chosen purposefully, and many sampling strategies can be used.3 Although many sampling strategies are discussed in the literature, only some will be described in this c01umn.~ A hypothetical study will be described to illustrate some of the sampling strategies and decisions that a qualitative researcher may make. As the researcher explores and decides which actions to take, these deci- sions must be documented in a research journal, which serves as an audit trail for credibility defense.

AN EXAMPLE

that a researcher is a graduate nursing student who has been introduced to phenomenology. This nurse researcher has been practicing in women’s health for 12 years and wants to learn about the lived experiences of women needing hysterectomies. Experientially, this researcher has noticed an emotional

For illustration, let us suppose

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difference in women with infer- tility who need hysterectomies versus fertile women who need hysterectomies. By narrowing the interest to women with infer- tility, the sample also narrows. If the researcher was interested in all women who need hysterec- tomies, the sample would include women from many eth- nic groups, economic back- grounds, and age groups (eg, adolescents, older adults). Although the focus of this hypo- thetical study solves the gender issue, other studies may need to address gender inclusion criteria.

Usually, the broader the phe- nomenon under study, the larger the sample a researcher would need. To adequately sample to understand the experiences of all patients needing hysterectomies, the researcher would need repre- sentative women from different ethnic groups, socioeconomic classes, and age groups. This undertaking could be too broad and unrealistic. It would behoove a qualitative researcher to build one study upon another during his or her research career. For example, homogenous samples that describe particular sub- groups in detail could reflect the lived experiences of patients needing hysterectomies, such as

African American peri- menopausal women, adolescents, recent Hispanic immigrants, patients diagnosed with uter- ine cancer, patients with postpartum hemorrhage, and this current hypothetical study of infertility patients.

After many studies have been completed, a meta-analysis could be performed on the findings from each study to determine

commonalties of the lived expe- rience for all patients needing hysterectomies.

In our hypothetical study, the researcher decides to use criteri- on sampling. Two selection crite- ria could include self-report of

Recruiting people of various

backgrounds for a research study

is termed maximum variation.

infertility and women age 35 or older. Again, these criteria nar- row the sample. For sample recruitment, suppose this researcher lives in a large urban area with diverse ethnic repre- sentation. The researcher, there- fore, will have the ability to recruit from different areas, thus capturing different cultures and socioeconomic classes. This type of sampling is termed maximum v a r i a t i ~ n . ~ In addition to the pre- viously cited sampling criteria, another common sampling crite- rion used is the requirement that participants must be English speaking because monolingual researchers often cannot and do not want to incur the expense of hiring translators.

OTHER FACTORS TO CONSIDER Qualitative researchers also

must determine how many par- ticipants are necessary. There is no single answer to this question. One indicator could be the sam-

ple size of similar types of pub- lished studies. As previously stated, another factor is the breadth and depth of the phe- nomenon under study. The sam- ple size also may be related to restraints of the researcher’s time, budget, and geographic location. When the phenomenon under study is extremely narrow, it may be difficult to recruit enough participants. Sometimes a snowballing sampling tech- nique is used to recruit addition- al participants from those already selected to participate in the study. For example, if the researcher interviews a patient with infertility who underwent a hysterectomy, the researcher may ask this patient whether she knows of anyone else with a similar experience. This patient’s recommendation may lead to the addition of another research participant.

A pilot study always is recom- mended. Pilot data may con- tribute to additional sampling cri- teria. Consider another hypotheti- cal example with this study. After interviewing four or five partici- pants in a pilot study, the researcher discovers that two of the participants had recently gone through a divorce. Through data analysis, the researcher finds that most of the data and the inter- view transcript relate to the issue of divorce rather than infertility or hysterectomy. The researcher, therefore, may add a sampling criterion that requires participants to be married to the same partner for the previous 10 years.

Qualitative researchers fre- quently perform data analysis con- currently with data collection. So, in the midst of a study, how can the researcher know when there are enough participants and, thus,

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enough data? The completion of data collection and the resulting subject size may be the result of data saturation. After enough data have been collected to determine themes or categories, the researcher may decide that if the next few participants’ experiences are captured by the existing themes or categories, the phenom- enon of study is saturated or com- plete. This means that the researcher’s construct represents

NOTES 1. E W Minium, B M King, G R

Bear, Statistical Reasoning in Psychology and Education, third ed (New York John Wiley & Sons, Inc, 1993) 23.

2. N Bums, S K Grove, The Practice of Nursing Research: Conduct, Critique & Utilization, sec-

the phenomenon of study, and no further data collection is necessary.

CONCLUSION In conclusion, qualitative

researchers perform sampling with a purpose. It is incumbent on the researcher to describe the sample in regards to gender, eth- nicity, age, socioeconomic class, and any other relevant criteria so research consumers can under- stand how and why this sample

ond ed (Philadelphia: W B Saunders Co, 1993) 451-492.

3. M Q Patton, Qualitative Evaluation and Research Methods, second ed (Newbury Park, Calif: Sage Publications, 1990) 143-198; I T Coyne, “Sampling in qualitative research. Purposeful and theoretical sampling; merging or clear bound-

was chosen. Many strategies influence sample size and selec- tion. The researcher must docu- ment the decision-making process involved in qualitative sampling to provide credibility for the research findings. Next month’s column will address evaluating the credibility of qualitative research.

MICHELLE BYRNE RN, MS, PHD, CNOR

NURSING RESEARCH COMMIITEE

aries?’ Journal of Advanced Nursing 26 (September 1997) 623-630.

4. Ibid. 5. M Sandelowski, “Sample size

in qualitative research,” Research in Nursing and Health 18 (April 1995) 179-183.

National Muscular Dystrophy Registry Established The National Institute of Arthritis and Musculo- skeletal and Skin Diseases and the National Institute of Neurological Disorders and Stroke have estab- lished a national registry for myotonic dystrophy (DM) and facioscapulohumeral dystrophy (FSHD), according to a Dec 11,2000, news release from the National Institutes of Health (NIH). Registry scien- tists will identify and classify patients with clinically diagnosed forms of DM and FSHD and store their medical and family histories.

The registry will be a central information source for researchers studying these diseases. Recommendations regarding enrollment criteria, monitoring and improving ways to recruit patients and investigators, and assessing programs will be made by the registry’s scientific advisory commit- tee. This committee also will revise and extend data collection and handling methods and determine possible clinical studies.

including DM and FSHD. These diseases can be detected at birth, may be passed from one generation to the next, and may cause progressive, disabling weakness. Additionally, DM may result

There are nine types of muscular dystrophy,

in sudden death. Congenital, juvenile, adult, and late onset are

the four types of DM. The disease is marked by a slow progression of weakness and muscle wasting affecting the face, feet, hands, neck, and glandular system. Muscles are unable to relax after contrac- tion. Both males and females may be affected with DM, and the cause of the disease is unknown.

In contrast, FSHD may progress either slowly or rapidly. It is marked by weakness in the facial muscles and weakness and wasting of the shoul- ders and upper arms. Both males and females may be affected. A child whose parent is affected has a 50% risk of inheriting the disease. The cause of FSHD, the third most common genetic disease of skeletal muscle, is unknown.

Currently, patient enrollment for the registry is scheduled to begin in the fall of 2001. The project is funded under the NIH contract NO1-AR-02250.

National Regishy Established for Two Muscular Dystrophy Types (news release, Bethesdo, Md: National Institutes of Health) 1-2. Available from http://tvww.nih.gov/newdpr /dec2OOO/niams- 1 1. htm. Accessed 1 1 Dec 2000.

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