15.6 General strengths and weaknesses of single-subject designs
There are three fundamental differences between single-subject designs and traditional group designs.
1. The first and most obvious distinction is that single-subject research is conducted with only one participant or occasionally a very small group.
2. Single-subject research also tends to be much more flexible than a traditional group study. A single-subject design can be modified or completely changed in the middle of a study without seriously affecting the integrity of the design, and there is no need to standardize treatment conditions across a large set of different participants.
3. Single-subject designs require continuous assessment. In a traditional group design, an individual subject typically is observed and measured only once or twice. A single-subject design, however, normally involves a series of 10 to 20 observations for each individual.
As a consequence of these differences, single-subject designs have some advantages and some disadvantages in comparison with group designs. In this section, we identify and discuss the general strengths and weakness of single-subject research, beginning with the strengths.
Advantages of single-subject designs
The primary strength of single-subject designs is that they allow researchers to establish cause-and-effect relationships between treatments and behaviors using only a single participant. This simple fact makes it possible to integrate experimental research into applied clinical practice. As we noted in Chapters 7 and 10, the demands and restrictions of traditional group experiments are often at odds with conducting research in natural settings such as a clinic with real clients. As a result, clinicians tend to prefer alternative strategies such as case studies or quasi-experimental research. However, these alternative strategies do not permit clinicians to establish causal relations between the treatments they use and the resulting behaviors. As a result, clinical psychologists are often left in the unenviable position of using treatments that have not been scientifically demonstrated to be effective. Single-subject designs provide a solution to this dilemma. By employing single-subject designs, a clinician who typically works with individual clients or small groups can conduct experimental research and practice therapy simultaneously without seriously compromising either activity. By recording and graphing observations during the course of treatment, a clinician can demonstrate a cause-and-effect relationship between a treatment and a client’s behavior. This scientific demonstration is an important part of establishing accountability in the field of clinical psychology. That is, clinicians should be able to demonstrate unambiguously that the treatments they use are effective.
A second major advantage of single-subject designs comes from their flexibility. Although a researcher may begin a single-subject experiment with a preconceived plan for the design, the ultimate development of the design depends on the participant’s responses. If a participant fails to respond to treatment, for example, the researcher is free to modify the treatment or change to a new treatment without compromising the experiment. Once again, this characteristic of single-subject research makes these designs extremely well suited to clinical research. In routine clinical practice, a therapist monitors a client’s response and makes clinical decisions based on those responses. This same flexibility is an integral part of most single-subject research. That is, the clinical decision to begin a new treatment and the experiment decision to begin a new phase are both determined by observing the participant’s response to the current treatment or current phase. In addition, single-subject designs allow a clinician/researcher to individualize treatment to meet the needs of a specific client. Because these designs typically employ only one participants, there is no need to standardize a treatment across a group of individuals with different needs, different problems, and different responses.
In summary, the real strength of single-subject designs is that they make experimental clinical research compatible with routine clinical practice. These designs combine the clinical advantages of case study research with the rigor of a true experiment. In particular, single-subject research allows for the detailed description and individualized treatment of a single participant, and allows a clinician/researcher to establish the existence of a cause-and-effect relationship between the treatment and the participants’ responses.
Disadvantages of single-subject designs
Earlier, we noted that one of the strengths of a single-subject design is that it can establish the presence of a cause-and-effect relationship using only one participant. At the same time, however, a weakness of these designs is that the relationship is demonstrated only for one participant. This simple fact leaves researchers with some question as to whether the relationship can or should be generalized to other individuals. You should recognize this problem as the general concern of external validity. However, the problem of limited external validity is mitigated by the fact that single-subject research seldom exists in isolation. Usually, the researcher or clinician has observed the treatment effect in multiple cases before one individual case is selected for the single-subject research project. Also, the relationship between the treatment and outcome is commonly demonstrated in other nonexperimental research such as case studies or quasi-experimental studies. These other studies provide support for generalizing the treatment effect (external validity), and the single-subject study demonstrates the causal nature of the effect (internal validity).
A second potential weakness of single-subject designs comes from the requirement for multiple, continuous observations. If the observations can be made unobtrusively, without constantly interrupting or distracting the participant, there is little cause for concern. However, if the participant is aware that observations are continuously being made, this awareness may result in reactivity or sensitization that could affect the participant’s responses (see Chapter 6). As a result, there is some risk that the participant’s behavior may be affected not only by the treatment conditions but also by the assessment procedures. In experimental terminology, the continuous assessment can be a threat to internal validity.
Another concern for single-subject designs is the absence of statistical controls. With traditional group designs, researcher can use standard inferential statistical techniques to quantify the likelihood that the results show a real treatment effect versus the likelihood that the results simply reflect chance behavior. Single-subject designs, on the other hand, relay on the visual effect of a graph to convince others that the treatment effects are real. Problems can arise if there is any ambiguity at all in the graphed results. One observer, for example, may see clear indications of a treatment effect, whereas other observers may not. On the positive side, reliance on graphed results helps ensure that researchers report only results that are substantial; that is, the treatment effects must be sufficiently large that they are obvious to a casual observer when presented in a graph. Researchers often make a distinction between statistical significance and practical significance or clinical significance. Practical significance means that the treatment effect is substantial and large enough to have practical application. A statistically significant result, on the other hand, simply means that the observed effect, whether large or small, is very unlikely to have occurred by chance. Using this terminology, the results from a single-subject study tend to have practical significance, although they typically are not evaluated in terms of statistical significance.
The reliance on a graph to establish the significance of results places additional restrictions on the application of single-subject designs. Specifically, the treatment effects must be large and immediate to produce a convincing graph. Treatments that produce small effects or effects that are slow to develop can generate ambiguous graphs and, therefore, are unlikely to appear in published reports. As a result, single-subject research is likely to fail to detect such effects. From a research perspective, this tendency is unfortunate because many real treatments are overlooked. From a clinician’s point of view, however, this aspect of single-subject research simply means that marginally effective treatments are weeded out and only those treatments that are truly effective are reported.
Chapter summary
In this chapter, we examined the characteristics of single-subject designs. The general goal of single-subject research, like other experimental designs, is to establish the existence of a cause-and-effect relationship between variables. The defining characteristic of a single-subject study is that it can be used with a single individual, by testing or observing the individual before and during or after the treatment implemented by the researcher.
The basic building block of most single-subject designs is the phase, a series of observations all made under the same conditions. Observations are made in a baseline phase (that is, in the absence of a treatment) and in a treatment phase (that is, during treatment). The series of observations that make up any phase should show a clear pattern that describes the behavior. The pattern within a factor is the consistency or stability of the pattern. Ultimately, the researcher changes phases by implementing or withdrawing a treatment. The purpose for a phase change is to demonstrate that adding or removing a treatment
15.6 ทั่วไปจุดแข็งและจุดอ่อนของการออกแบบเรื่องเดียว มีความแตกต่างพื้นฐานสามระหว่างออกแบบเรื่องเดียวและแบบกลุ่มดั้งเดิม1. ความแตกต่างแรก และเห็นได้ชัดที่สุดคือ ที่ดำเนินการวิจัยเรื่องเดียวตรงกับตำแหน่งหรือเป็นกลุ่มเล็ก ๆ2 วิจัยเรื่องเดียวยังมีแนวโน้มที่ มีความยืดหยุ่นมากขึ้นกว่าการศึกษาแบบกลุ่ม แบบเรื่องเดียวสามารถปรับเปลี่ยน หรือเปลี่ยนแปลงอย่างสมบูรณ์ระหว่างการศึกษา โดยไม่มีผลกระทบต่อความสมบูรณ์ของการออกแบบอย่างจริงจัง และไม่จำเป็นต้องกำหนดมาตรฐานเงื่อนไขการรักษาข้ามชุดใหญ่ของผู้เข้าร่วมที่แตกต่างกัน3. เรื่องเดียวออกแบบจำเป็นต้องประเมินอย่างต่อเนื่อง ในแบบดั้งเดิมกลุ่ม การแต่ละเรื่องโดยทั่วไปสังเกต และวัดเพียงครั้งเดียวหรือสอง แบบเรื่องเดียว อย่างไรก็ตาม โดยปกติเกี่ยวข้องกับชุดสังเกต 10-20 สำหรับแต่ละบุคคลเป็นลำดับของความแตกต่างเหล่านี้ ออกแบบเรื่องเดียวมีบางข้อดีและข้อเสียบางอย่างเมื่อเปรียบเทียบกับกลุ่มออกแบบ ในส่วนนี้ เราสามารถระบุ และอภิปรายทั่วไปจุดแข็งและจุดอ่อนของงานวิจัยเรื่องเดียว เริ่มต้น ด้วยจุดแข็งข้อดีของการออกแบบเรื่องเดียว The primary strength of single-subject designs is that they allow researchers to establish cause-and-effect relationships between treatments and behaviors using only a single participant. This simple fact makes it possible to integrate experimental research into applied clinical practice. As we noted in Chapters 7 and 10, the demands and restrictions of traditional group experiments are often at odds with conducting research in natural settings such as a clinic with real clients. As a result, clinicians tend to prefer alternative strategies such as case studies or quasi-experimental research. However, these alternative strategies do not permit clinicians to establish causal relations between the treatments they use and the resulting behaviors. As a result, clinical psychologists are often left in the unenviable position of using treatments that have not been scientifically demonstrated to be effective. Single-subject designs provide a solution to this dilemma. By employing single-subject designs, a clinician who typically works with individual clients or small groups can conduct experimental research and practice therapy simultaneously without seriously compromising either activity. By recording and graphing observations during the course of treatment, a clinician can demonstrate a cause-and-effect relationship between a treatment and a client’s behavior. This scientific demonstration is an important part of establishing accountability in the field of clinical psychology. That is, clinicians should be able to demonstrate unambiguously that the treatments they use are effective. A second major advantage of single-subject designs comes from their flexibility. Although a researcher may begin a single-subject experiment with a preconceived plan for the design, the ultimate development of the design depends on the participant’s responses. If a participant fails to respond to treatment, for example, the researcher is free to modify the treatment or change to a new treatment without compromising the experiment. Once again, this characteristic of single-subject research makes these designs extremely well suited to clinical research. In routine clinical practice, a therapist monitors a client’s response and makes clinical decisions based on those responses. This same flexibility is an integral part of most single-subject research. That is, the clinical decision to begin a new treatment and the experiment decision to begin a new phase are both determined by observing the participant’s response to the current treatment or current phase. In addition, single-subject designs allow a clinician/researcher to individualize treatment to meet the needs of a specific client. Because these designs typically employ only one participants, there is no need to standardize a treatment across a group of individuals with different needs, different problems, and different responses. In summary, the real strength of single-subject designs is that they make experimental clinical research compatible with routine clinical practice. These designs combine the clinical advantages of case study research with the rigor of a true experiment. In particular, single-subject research allows for the detailed description and individualized treatment of a single participant, and allows a clinician/researcher to establish the existence of a cause-and-effect relationship between the treatment and the participants’ responses.
Disadvantages of single-subject designs
Earlier, we noted that one of the strengths of a single-subject design is that it can establish the presence of a cause-and-effect relationship using only one participant. At the same time, however, a weakness of these designs is that the relationship is demonstrated only for one participant. This simple fact leaves researchers with some question as to whether the relationship can or should be generalized to other individuals. You should recognize this problem as the general concern of external validity. However, the problem of limited external validity is mitigated by the fact that single-subject research seldom exists in isolation. Usually, the researcher or clinician has observed the treatment effect in multiple cases before one individual case is selected for the single-subject research project. Also, the relationship between the treatment and outcome is commonly demonstrated in other nonexperimental research such as case studies or quasi-experimental studies. These other studies provide support for generalizing the treatment effect (external validity), and the single-subject study demonstrates the causal nature of the effect (internal validity).
A second potential weakness of single-subject designs comes from the requirement for multiple, continuous observations. If the observations can be made unobtrusively, without constantly interrupting or distracting the participant, there is little cause for concern. However, if the participant is aware that observations are continuously being made, this awareness may result in reactivity or sensitization that could affect the participant’s responses (see Chapter 6). As a result, there is some risk that the participant’s behavior may be affected not only by the treatment conditions but also by the assessment procedures. In experimental terminology, the continuous assessment can be a threat to internal validity.
Another concern for single-subject designs is the absence of statistical controls. With traditional group designs, researcher can use standard inferential statistical techniques to quantify the likelihood that the results show a real treatment effect versus the likelihood that the results simply reflect chance behavior. Single-subject designs, on the other hand, relay on the visual effect of a graph to convince others that the treatment effects are real. Problems can arise if there is any ambiguity at all in the graphed results. One observer, for example, may see clear indications of a treatment effect, whereas other observers may not. On the positive side, reliance on graphed results helps ensure that researchers report only results that are substantial; that is, the treatment effects must be sufficiently large that they are obvious to a casual observer when presented in a graph. Researchers often make a distinction between statistical significance and practical significance or clinical significance. Practical significance means that the treatment effect is substantial and large enough to have practical application. A statistically significant result, on the other hand, simply means that the observed effect, whether large or small, is very unlikely to have occurred by chance. Using this terminology, the results from a single-subject study tend to have practical significance, although they typically are not evaluated in terms of statistical significance.
The reliance on a graph to establish the significance of results places additional restrictions on the application of single-subject designs. Specifically, the treatment effects must be large and immediate to produce a convincing graph. Treatments that produce small effects or effects that are slow to develop can generate ambiguous graphs and, therefore, are unlikely to appear in published reports. As a result, single-subject research is likely to fail to detect such effects. From a research perspective, this tendency is unfortunate because many real treatments are overlooked. From a clinician’s point of view, however, this aspect of single-subject research simply means that marginally effective treatments are weeded out and only those treatments that are truly effective are reported.
Chapter summary
In this chapter, we examined the characteristics of single-subject designs. The general goal of single-subject research, like other experimental designs, is to establish the existence of a cause-and-effect relationship between variables. The defining characteristic of a single-subject study is that it can be used with a single individual, by testing or observing the individual before and during or after the treatment implemented by the researcher.
The basic building block of most single-subject designs is the phase, a series of observations all made under the same conditions. Observations are made in a baseline phase (that is, in the absence of a treatment) and in a treatment phase (that is, during treatment). The series of observations that make up any phase should show a clear pattern that describes the behavior. The pattern within a factor is the consistency or stability of the pattern. Ultimately, the researcher changes phases by implementing or withdrawing a treatment. The purpose for a phase change is to demonstrate that adding or removing a treatment
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