Clinical Treatment Outcome Research Paper

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The essential paradigm for determining if a treatment is effective is to compare it with something else. However, the issue of what that ‘something else’—a control or comparison group—should be in any given clinical trial is quite complicated and has enormous theoretical and practical implications. This research paper will briefly review the role of control and comparison conditions in clinical treatment outcome research and describe advantages and disadvantages of several different types of control and comparison designs. For readers interested in more detailed review of this important area, the classic texts by Kazdin (1980, 1998) are excellent sources.

1. Background

The randomized controlled trial is the sine qua non of treatment efficacy research. A given treatment cannot be considered ‘empirically validated’ (see Chambless and Hollon 1998) unless trials purporting to establish its effectiveness have employed at least two fundamental methodological features: (a) a credible control condition, and (b) random assignment to the experimental and control conditions. These critical features offer enormous advantages in evaluating a treatment’s efficacy. For example, random assignment of participants to the experimental vs. control condition is essential in ruling out alternate explanations of findings, including regression to the mean, maturation, history, effects of repeated testing, and selection basis (Kazdin 1998). The selection of an appropriate comparison or control group also is essential in determining, all other things being equal, if a treatment is effective for a given disorder, and whether it has benefits relative to other treatments for the disorder, as well as how it may achieve its effects and what its ‘active ingredients’ may be.

2. What Should Control Groups Control For?

The historical paradigm for control groups in behavioral research is the placebo control for pharmaco-therapy efficacy trials. Placebo (I shall please) controls provide a means of evaluating a pharmacotherapy’s efficacy compared with those ‘placebo’ or ‘non-specific’ effects which may occur simply because participants believe they are receiving a credible treatment (Frank 1961). Placebo effects in pharmaco-therapy trials, which may be associated with substantial and durable improvement, may occur because of participants’ expectations of improvement, demand characteristics, the instillation of hope, the provision of support and education, and other non-specific effects that are associated with simply being in treatment. Thus, because (a) the pill (or, sometime, injection) in placebo control conditions is medically inert, and (b) nonspecific elements are assumed to be comparable in the ‘active medication’ and pill placebo conditions, differences in outcome are assumed to be due to the unique ‘active ingredients’ of the experimental medication.

However, the issue of what constitutes an appropriate ‘placebo’ condition (and even if the term ‘placebo’ is appropriate for control conditions in behavioral research) in psychotherapy efficacy re-search is much more complex and has been the subject of much controversy for many years (see Critelli and Neumann 1984, O’Leary and Borkovec 1978, Parloff 1986, Wilkins 1986). Soon after Rosenthal and Frank (1956) declared that the only adequate control condition in psychotherapy research was a placebo group, several problems with this strategy were raised. Defining a ‘psychologically inert’ approach that is an appropriate ‘placebo’ control for behavioral research raised a number of conceptual, practical, and ethical concerns (O’Leary and Borkovec 1978).

Conceptually, defining an appropriate nonspecific control condition for psychotherapy is difficult be-cause many of the ‘nonspecific’ elements that are common to many psychotherapies (e.g., formation of a therapeutic alliance, provision of support and education, and the instillation of hope) are not inert, in that they are associated with legitimate psychological processes of change and have been shown to have powerful effects on psychological conditions (O’Leary and Borkovec 1978). Moreover, Parloff (1986) noted that referring to these ‘common elements’ or ‘nonspecific elements’ as placebos suggests that these powerful mechanisms of change are somehow spurious.

Practically, it can be difficult to conceive of a psychologically inert approach (e.g., an approach that has no theoretically supported rationale for influencing the behavior in question) that is sufficiently credible to participants (O’Leary and Borkovec 1978). This is particularly difficult in the case of lengthy trials where it is essential to retain participants in those conditions over periods of several weeks or months. Furthermore, there has been little agreement on what constitutes an acceptable ‘placebo’; thus, there is no single, widely recognized or standardized placebo condition. This makes comparison of effect sizes (a standardized estimate of the magnitude of the effect of the experimental condition relative to the control) across studies very complex (Parloff 1986). This can pose problems, for example, in meta-analyses aimed at comparing the effect sizes for different types of behavioral approaches for a given disorder.

Ethically, for many treatment-seeking populations it is highly questionable whether providing a placebo—a treatment that is expected to have no effect on the presenting problem—can be justified. Furthermore, many placebo conditions, in presenting a credible rationale but no interventions that are expected to improve the participant’s problem, are also inherently deceptive (Kazdin 1980, O’Leary and Borkovec 1978).

Given these issues, a variety of different control conditions have been proposed for psychotherapy research. Several of the most common will be described below.

3. Types Of Control Groups

3.1 No-Treatment Controls

This strategy compares the experimental approach to no treatment; addressing the question ‘Does this treatment work better than no treatment at all?’ In this paradigm, participants are assessed, randomized to treatment condition, and reassessed after completion of treatment (or after an equivalent length of time for the no-treatment control group).

3.1.1 Advantages. No-treatment controls are generally seen as the ‘minimal’ or basic standard for evaluating the effectiveness of an intervention (Chambless and Hollon 1998). No treatment control conditions are sometimes referred to as assessment-only controls, as they control for the effects of the study assessments and the passage of time. Thus, they are useful in evaluating conditions that have a high likelihood of improving without intervention (e.g., spontaneous remission) or when the natural history of a disorder is not well established.

3.1.2 Disadvantages. There are a number of problems with no-treatment control conditions. No-treatment controls do not control for the effects of participant expectancies, ‘common elements’ or nonspecific effects, or time spent in treatment. Ethical and practical issues arise when no-treatment controls are used with populations seeking treatment for a particular condition, and particularly when the condition is life-threatening or associated with significant medical, psychosocial, or other problems. Further-more, withholding treatment from individuals who request it raises ethical issues, particularly for those dis-orders where effective alternative treatments have been demonstrated to exist. No-treatment controls may also raise practical issues, because individuals assigned to the no-treatment condition may seek alternative therapies or become demoralized and drop out of the study, particularly for more lengthy trials. This can lead to problems associated with con-founding of conditions or differential attrition.

Some of the practical and ethical concerns associated with no-treatment control conditions can be avoided in designs where the experimental treatment is ‘added on’ to a standard treatment program and the control group receives the standard treatment only. Thus, all participants would, at minimum, receive the standard treatment. This design addresses the question, ‘Does the addition of Intervention X improve outcomes over standard treatment for this disorder’ and avoids many ethical and practical problems. However, this strategy still does not control for time spent or nonspecific effects.

3.2 Wait List Delayed Treatment Controls

This strategy is similar to the no-treatment control approach, but differs in that some form of treatment is offered to those assigned to the no-treatment control condition after completion of study assessments. Thus, after completing all past treatment assessments, participants originally assigned to the delayed-treatment condition may be given the option of no further treatment or receiving the experimental treatment or an alternative approach.

3.2.1 Advantages. Like the no-treatment control condition, this strategy is one that addresses the question, ‘Is Treatment X effective compared with no treatment?’ and can help clarify the effects of the experimental intervention with respect to the natural history of the disorder. Provided that participants in the delayed treatment control are adequately monitored and the disorder of interest is one where the likelihood of clinical exacerbation and negative consequences are minimal, this strategy avoids some of the ethical problems associated with withholding treatment from individuals who need or request it. Some prospective participants who might not accept randomization to a no-treatment control condition may be more likely to accept randomization to a delayed treatment control.

3.2.2 Disadvantages. Like the no-treatment control strategy, delayed treatment controls do not control for differences in nonspecific effects of treatment, including expectancies, demand characteristics, attention, and so forth. Moreover, evaluation of long-term effects of treatments is difficult with delayed treatment controls, as provision of treatment to the participants in the delayed-treatment condition may obfuscate determination of long-term effectiveness of the treatment in follow-up evaluations. This can, of course, be avoided by waiting to provide treatment to the delayed-treatment condition until after the completion of all follow-up assessments, but this may in turn result in the same practical and ethical problems associated with no-treatment controls.

3.3 Attention Discussion Minimal Treatment Controls

This strategy most closely resembles what has been referred to as a psychotherapy ‘placebo.’ In this paradigm, the participants are assigned to a condition that provides some common elements of psycho-therapy (e.g., time spent, presentation of a credible rationale for the approach, receiving support and attention), but does not offer the hypothesized ‘active ingredients’ of the experimental intervention. The specific nature of this type of control group varies widely from trial to trial, but may include interventions such as having the participants meet with a clinician who provides education and support, ‘discussion control’ groups where several participants meet to provide mutual support or are presented with education materials, ‘bibliotherapy’ conditions where participants receive written reading or other educational materials such as videotapes, and several more.

3.3.1 Advantages. Attention-control conditions, by controlling for time spent and providing some common elements of psychotherapy, are typically seen as more stringent control than no-treatment or delayed-treatment control conditions. If well-conceived, care-fully implemented and monitored attention controls can provide a test of the hypothesized active ingredients of the experimental condition and may allow for some evaluation of mechanisms of action of the experimental condition, which is not usually feasible with no-treatment or delayed-treatment controls.

3.3.2 Disadvantages. As noted above, there have been several problems with attention discussion control conditions. First, it is unclear whether many of these approaches actually adequately control for non-specific elements of the experimental intervention (Basham 1986). Second, given that a key ingredient of such approaches is the presentation of a convincing rationale, but at the same time the intervention ‘… should have no currently supported theoretical reason why the placebo would influence the behavior under question’ (O’Leary and Borkovec 1978, p. 821), a truly convincing rationale for these conditions is not so easily formulated. If participants are not convinced or do not see themselves as deriving adequate benefit from the approach, they may be more likely to drop out of the condition, leading to problems of differential attrition in the control vs. experimental condition. Furthermore, since the attention discussion is intended to be ‘inert’ and not directly affect the disorder or problem, ethical questions regarding the withholding of treatment may be raised for those conditions where effective alternative approaches exist. Finally, as noted above, because there has been little consensus on what such controls should consist of (either within or across different disorders), attention control conditions vary widely from study to study, making cross-study comparisons difficult.

3.4 Active Treatment Or Comparative Controls

In this strategy, the experimental intervention is compared with another ‘active’ intervention, ideally one of demonstrated efficacy for the disorder. Thus, a comparative design directly compares two treatment conditions without conceptualizing either as being a formal control group (Basham 1986). Rather than addressing the issue of ‘Does this treatment work?’ this strategy addresses questions such as ‘Is Treatment A more effective than Treatment B’ and ‘Does Treatment A offer advantages over standard treatment for this disorder?’ It should be noted that for many disorders, the comparison condition may be a psycho-therapy or a pharmacotherapy.

3.4.1 Advantages. When well-conceived and executed, comparison controls do control for many artifacts and demand characteristics, including time spent in treatment, the provision of a credible rationale, and other common elements or nonspecific effects (although it should be noted that equivalence of nonspecific elements across conditions must be sup-ported by process evaluations). This strategy has the additional advantage of permitting more thorough evaluation of treatment process and mechanisms of action, and it can help identify what treatment is best for a given disorder, as well as what type of treatment is best for what type of individual (Basham 1986, Kazdin 1986, O’Leary and Borkovec 1978). Furthermore, by comparing the experimental intervention to a treatment of demonstrated efficacy for the disorder (e.g., a ‘standard’ or ‘reference’ condition), this approach avoids deception and many of the ethical problems discussed earlier.

3.4.2 Disadvantages. Comparison controls, by con-trolling for nonspecific elements and essentially pit-ting the hypothesized ‘active ingredients’ of one approach against those of another, are highly stringent tests of novel interventions. Thus, such studies often lead to small effect sizes and findings of no significant differences between interventions (Luborsky et al. 1975), which in turn may lead to problems in interpretation of the study outcomes. For example, in a trial comparing two active treatments where no significant difference in effectiveness is found, interpretation of the ‘absolute’ effectiveness of the treatments is problematic. That is, although the treatments compared were not significantly different, it is often hard to gauge the magnitude of the effect of either treatment on the symptoms targeted (Nathan 1997). Kazdin (1986) has also pointed out that comparative designs may overemphasize elements that differentiate the treatments compared (e.g., use of specific techniques) over other important variables that may affect outcome (e.g., characteristics of therapists or participants). Finally, for those disorders where a number of viable comparison approaches are available, but no one clear standard or ‘reference’ condition that is widely acknowledged as the most effective, choice of the comparison condition is challenging. Kazdin (1986) has provided thoughtful recommendations for the selection and implementation of appropriate active treatment control conditions.

The relative stringency of comparison controls relative to attention discussion, delayed-treatment, or no-treatment controls has practical implications as well. For example, within a given field, if one type of intervention (Treatment A) routinely uses no-treatment controls in efficacy studies, while another type of intervention (Treatment B) uses discussion control conditions, while trials evaluating Treatment C routinely use active treatment controls, the estimated effect size of Treatment A is likely to be larger than that for Treatment B, which is in turn likely to be larger than for Treatment C, even though all three approaches may be comparably effective. Progressively smaller effect sizes for different types of control conditions (no treatment, placebo, active treatment) has been suggested in several meta-analyses (Basham 1986).

3.5 Dismantling Controls

Also referred to as component control condition, this strategy essentially requires specification of a given treatment or treatment ‘package’ into its component elements, and then evaluating the effectiveness of the treatment with or without one specific element or technique of interest. For example, a cognitive behavioral approach might be evaluated with and without a relaxation training component.

3.5.1 Advantages. By altering only a single element of a treatment, component control strategies offer an elegant strategy for evaluating well-defined techniques and components. Component control conditions can address issues of particular theoretical or clinical relevance, by isolating the most effective ‘ingredients’ of complex or multifaceted treatment packages. Furthermore, because the interventions compared differ only with respect to a single element, many of the practical, ethical, and theoretical issues associated with placebo and no-treatment controls can be avoided (O’Leary and Borkovec 1978).

3.5.2 Disadvantages. Before treatments or treatment packages can be dismantled, they must first be demonstrated to be effective. Thus, for a given dis-order, there may only be a small number of approaches with sufficient empirical support that would justify their ‘dissection’ in a dismantling study. Similarly, not all approaches are easily parsed into discrete components. Furthermore, to justify a full dismantling trial, a compelling rationale for the component to be evaluated must be made, e.g., the component might be ‘… very risky, costly, or theoretically interesting’ (Strayhorn 1987).

3.6 Pill Placebo Conditions

Citing the problems noted above with placebo conditions for psychotherapy research, Klein (1997) and others have argued for wider use of pill placebo controls for psychotherapy trials. In this strategy, the experimental psychotherapy would be compared with a pill placebo condition. This strategy was used in the landmark NIMH Treatment of Depression Collaborative Research Program (Elkin et al. 1985), which compared cognitive therapy and interpersonal psycho-therapy to a placebo clinical management condition (with imipramine clinical management as a reference condition).

3.6.1 Advantages. The use of pill placebo conditions in psychotherapy research has a number of potential advantages. First, when carefully implemented, pill placebos provide control for participant expectations and many demand characteristics. Klein (1997) also points out that this approach enables researchers to evaluate psychotherapy effects in the context of a pharmacotherapy-responsive population. This approach avoids problems with ‘psychotherapy placebo’ conditions, as it compares the effects of a given psychotherapy with those nonspecific effects of a pill placebo. This strategy may also allow clearer evaluation of treatment processes and mediation effects (Crits-Christoph 1997).

3.6.2 Disadvantages. Pill placebo controls require the availability of a widely recognized effective pharmacotherapy for the disorder in question, as the rationale for the pill placebo control requires that participants expect to improve by taking the pill. Thus, a major drawback of this approach is that for many conditions for which psychotherapies may be appropriate, no such reference pharmacotherapy exists. Moreover, because most pharmacotherapies are delivered in conjunction with a minimal supportive psycho-therapy condition to foster compliance and enhance retention (conditions which closely resemble placebo psychotherapies), the problems associated with conceiving and implementing minimal or placebo psycho-therapies may not be avoided entirely (Carroll 1997).

4. Summary

Just as there is no one ‘perfect’ clinical trial, there is no one perfect control group. The particular control group selected does determine, however, the nature of the questions that can be addressed by the trial (e.g., ‘Does this treatment work’ to ‘Does this treatment work for the reasons we believe it does’ to ‘Does this treatment have specific benefits compared with other available treatments?’).

Selection of an optimal control condition for a given study thus depends on many factors, including the level of development of the treatment being evaluated, the availability of alternative treatments for the disorder, the severity or natural history of the disorder, and many others (Crits-Christoph 1997). Thus, early in the development of a field, where questions remain about a disorder’s natural course, and available treatments are scarce, no-treatment or delayed treatment controls may be appropriate choices. However, as a field becomes more sophisticated and alternative treatments are identified, research questions also become more fully developed and require the use of control groups that can address progressively more complex questions.

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