This has been the topic of important recent methodological research, including studies of the interobserver reliability of expert judgements of changes seen in published multiple baseline designs (Wolfe et al., 2016) and use of simulated data to test Type I and II error rates when judgements of experimental control are made based on different numbers of tiers (Lanovaz & Turgeon, 2020). However, it does not rule out maturation as an alternative explanation of the change in behavior. Rather, the passage of time allows for more opportunities for participants to interact with their environmentleading to maturational changes. Type I Errors and Power in Multiple Baseline Designs, Assessing consistency of effects when applying multilevel models to single-case data. The within-tier analysis seeks replication of these potential treatment effects in additional tiers of the design. For example, Gast et al. This argument rests on the assumptions that any extraneous variable that affects one tier will (1) contact all tiers and (2) have a similar effect on all tiers. Type I errors and power in multiple baseline designs. Single-case intervention research design standards. An alternative explanation would have to suggest, for example, that in one tier, experience with 5 baseline sessions produced an effect coincident with the phase change; in a second tier, 10 baseline sessions had this effect, again coinciding with the phase change; and in a third tier, 15 baseline sessions produced this kind of change and happened to correlate with the phase change. Google Scholar. Further, if the potential treatment effect is more gradual (as one might expect from an educational intervention on a complex skill), maturational changes may be impossible to distinguish from treatment effects. https://doi.org/10.1007/s40614-020-00263-x, Shadish, W. R., & Sullivan, K. J. They do not mention the across-tier comparison, presumably because they believe that this analysis is not necessary to establish experimental control. Recognizing these three dimensions of lag has implications for reporting multiple baseline designs. https://doi.org/10.1177/001440290507100203, Johnston, J. M., Pennypacker, H. S., & Green, G. (2020). Each replication requires an assumption of a separate event coinciding with a distinct phase change. Experimental and quasi-experimental designs for research. Concurrent multiple baseline designs are multiple baseline designs in which the tiers are synchronized in real time. Controlling for coincidental events requires attention to the specific dates on which events occur. Likewise, setting-level coincidental events are those that contact a single setting. However, this kind of support is not necessary: lagged replications of baseline predictions being contradicted by data in the treatment phase provide strong control for all of these threats to internal validity. Coincidental events might be expected to be more variable in their effect than interventions that are designed to have consistent effects. This statement, of course, fails to satisfy the operational desire for a specific number of tiers that accomplishes this function. On the other hand, across-tier comparisons may be strengthened by arranging tiers to be as similar as possible so that they would be more likely to be exposed to the same coincidental events. This would draw attention to the relationship between the prediction from baseline and the (possible) contradiction of that prediction by the obtained treatment-phase data, and the replication of this prediction-contradiction pair in subsequent tiers. Characteristics of single-case designs used to assess intervention effects in 2008. WebAB design advantages - -simple to use AB design disadvantages - -cannot be used to make a confident assumption of a functional relation -vulnerable to confounding variables -does not provide for replication AB design - basic single subject design AB design has two phases of design - A: Baseline B: Intervention Reversal Design referred to as - Smith, J. D. (2012). Each tier involves a unique participant and there is a class of coincidental events that contact a single participant. Book If a nonconcurrent multiple baseline has a long lag in real time between phase changes (e.g., weeks or months), this may provide stronger control than a design with a lag of one or several days. The general steps for the development of the line graphs are as follows: 1. For example, physical growth and experiences with the environment can accumulate and result in relatively sudden behavioral changes when a toddler begins to walk. So, similar to maturation, the across-tier comparison is sometimes able to reveal effects of testing and session experience, but it may fail to do so in some circumstances. Article The vast majority of contemporary published multiple baseline designs describe the timing of phases in terms of sessions rather than days or dates. Although it is plausible that an extraneous variables influence could coincide with one phase change, it is less plausible that such a coincidence would occur twice, and even less plausible that it would occur three times. Johnston, J. M., Pennypacker, H. S., & Green, G. (2010). AB Design. A : true B : false. Experimental and quasi-experimental designs for generalized causal inference. This information would allow readers to evaluate the sufficiency of each dimension of lag given the specific characteristics of the particular study. Coincidental events share the characteristic that their behavioral impact is expected to be a function of particular dates. The present article is focused on the second questionwhether systematic changes in data can be attributed to the treatment. The across-tier analysis of coincidental events is the main way that concurrent and nonconcurrent multiple baselines differ. The first is the reversal design and the authors describe the important applied limitation with this designsituations in which reversals are not possible or feasible in applied settings. WebMULTIPLE BASELINE DESIGN Most widely used for evaluating treatment effects in ABA Highly flexible Do not have to withdraw treatment variable Is an alternative to reversal For both types of comparisons, addressing maturation begins with an AB contrast in a single tier. Sidman, M. (1960). Carr (2005) invokes this prediction, verification, and replication logic, and concludes, The nonconcurrent MB design only controls for threats associated with maturation/exposure; it does not control for historical [coincidental events] threats to internal validity, as does a concurrent MB design (p. 220). He acknowledged that earlier authors had stated that multiple baselines must be concurrent and he noted that in a nonconcurrent multiple baseline the across-tier comparison could not reveal coincidental events. Google Scholar, Coon, J. C., & Rapp, J. T. (2018). In this case, the effects of this kind of event could be revealed through the across-tier comparison of participants or behaviors that have not been exposed to the independent variable. This certainty is increased by isolation of tiers in time and other dimensions. So, for example, session 10 in tier 2 must take place at some time between tier 1s session 9 and 11. The concurrent multiple baseline design opened up many new opportunities to conduct applied research in contexts that were not amenable to other SCDs. The replicated within-tier analysis looks to patterns of results within the other tiers. As we mentioned above, across-tier comparisons require the assumptions that coincidental events will (1) contact and (2) have similar effects on all tiers of the design. Tactics of scientific research. https://doi.org/10.1007/s40614-022-00343-0, SI: Commentary on Slocum et al, Threats to Internal Validity. The process begins with a simple baseline-treatment (AB) comparisona change from baseline to treatment within a single tier. Journal of Applied Behavior Analysis, 30(3), 533544. (p. 206). Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. Experimental and quasi-experimental designs of research. Exceptional Children, 71, 165179. Behavioral cusps: A developmental and pragmatic concept for behavior analysis. Multiple baseline designs are the workhorses of single-case design (SCD) research and are the predominant design used in modern applied behavior analytic research (Coon & Rapp, 2018; Cooper et al., 2020). If an effective treatment were to have a broad impact on multiple tiers, the logic of the design would be to falsely attribute these effects to possible extraneous variables. We use the term potential treatment effect to emphasize that the evidence provided by this single AB within-tier comparison is not sufficient to draw a strong causal conclusion because many threats to internal validity may be plausible alternative explanations for the data patterns. WebThe first quality of ideal baseline data is stability, meaning that they display limited variability. If the pattern of change shortly after implementation of the treatment is replicated in the other tiers after differing lengths of time in baseline (i.e., different amounts of maturation), maturation becomes increasingly implausible as an alternative explanation. It is clear that we cannot claim that these assumptions are always valid for multiple baseline designs. a potential treatment effect in the first tier would be vulnerable to the threat that the changes in data could be a result of Without these dimensions of lag explicitly stated in the definition, we cannot claim that multiple baseline designs will necessarily include the features required to establish experimental control. On resolving ambiguities of the multiple-baseline design: Problems and recommendations. When he turned to multiple baseline designs, Hayes argued that AB designs are natural to clinic work and that forming a multiple baseline can consist of collecting several AB replications, which would inevitably have differing lengths of baseline (i.e., a nonconcurrent multiple baseline; p. 206). Kazdin, A. E., & Kopel, S. A. (p. 325), Compared to its concurrent multiple baseline design sibling, a non-concurrent arrangement is inherently weaker . Journal of Behavior Therapy & Experimental Psychiatry, 12(3), 257259. However, ina concurrent multiple baseline across settings a setting-level event would contact only a single tierthe design would be inherently insensitive to these coincidental events. Behavioral Assessment, 7(2), 129132. These could include presence of observers, testing procedures, exposure to testing stimuli, attention from implementers, being removed from the typical setting, exposure to a special setting, and so on. Throughout this article we have referred to the importance of replicating within-tier comparisons, emphasizing the idea that tiers must be arranged with sufficient lag in phase changes so that specific threats to internal validity are logically ruled out. WebThe main disadvantage of the multiple baseline design is that a high degree of planning is required to produce a successful implementation. Second, we briefly summarize historical methodological writing and current textbook treatment of these designs. These baseline-treatment comparisons, which we will refer to as tiers, differ from one another with respect to participants, behaviors, settings, stimulus materials, and/or other variables. Or in a multiple baseline across settings that are assessed at different times of the day, a socially challenging event such as an increase in daily bullying on a morning bus ride could disrupt the target behavior of a participant for the first hour of the day, but have reduced effects thereafter. Second, as we have discussed above, the amount of lag between phase changes (in terms of sessions in baseline, days in baseline, and elapsed days) is the primary design feature that reduces the plausibility of any single threat accounting for changes in multiple tiers, and thereby threatening the internal validity of the design as a whole. This pattern seriously weakens the argument that the independent variable was responsible for the change in the treated tier. 7. Kazdin, A. E. (2021). https://doi.org/10.4324/9781315537085. Without the latter you cannot conclude, with confidence, that the intervention alone is responsible for observed behavior changes since baseline (or probe) data are not concurrently collected on all tiers from the start of the investigation. Although the across-tier comparison may detect some coincidental events; it cannot be assumed to detect them all. https://doi.org/10.1016/S0005-7894(75)80181-X, Kratochwill, T. R., Hitchcock, J., Horner, R. H., Levin, J. R., Odom, S. L., Rindskopf, D. M., & Shadish, W. R. (2013). write that after implementing the treatment in an initial tier, the experimenter perhaps notes little or no change in the other baselines (p. 94). The logic of replicated within-tier analysis applies equally to concurrent and nonconcurrent designs. https://doi.org/10.1007/s40614-022-00326-1, DOI: https://doi.org/10.1007/s40614-022-00326-1. Although the claims that nonconcurrent multiple baseline designs are weaker than concurrent multiple baselines, especially with respect to threats of coincidental events, are nearly universal in the current literature, none of these authors acknowledge or address, the arguments made by Watson and Workman (1981) and Hayes (1981) in support of these designs. In the end, judgments about the plausibility of threats and number of tiers needed must be made by researchers, editors, and critical readers of research. These coincidental events would contact all tiers of a multiple baseline that include this individual participant, but not tiers that do not involve this participant. We can strongly argue that all tiers contact testing and session experience during baseline because we schedule and conduct these sessions. In a review of the SCD literature, Shadish and Sullivan (2011) found multiple baseline designs making up 79% of the SCD literature (54% multiple baseline alone, 25% mixed/combined designs). They argue that because nonconcurrent multiple baseline designs lack an across-tier comparison in real time (the criticism described above), they cannot verify the prediction of the behavior pattern in the absences of intervention. Consequently, it is often difficult or impossible to dismiss rival hypotheses or explanations. Multiple baseline designs are intended to evaluate whether there is a functional (causal) relation between the introduction of the independent variable and changes in the dependent variable. - 216.238.99.111. (1968) who emphasized the replicated within-tier comparison. The functional answer to this question is that there must be sufficient tiers so that none of the threats to internal validity are plausible explanations for the pattern of effects across the set of tiers. Nonconcurrent multiple baseline designs for educational program evaluation. Hayes, S. C. (1985). Kennedy, C.H. Slocum, T.A., Pinkelman, S.E., Joslyn, P.R. Basic Books. Instead, the idea that lag across phase changes includes three important dimensions and that these lags are critical for establishing experimental control and justifying strong causal conclusions should be elevated in importance. This critical requirement is mainly addressed by the lag between phase changes in successive phases. This raises the question of how many replications are necessary to establish internal validity. For example, it is implausible that the effects of maturation would coincide with a phase change after 5 days in one tier, after 10 days in a second tier, and after 15 days in a third. Every multiple baseline design in which potential treatment effects are observed in some but not all tiers demonstrates that tiers are not always equally sensitive to interventions. Alternating Treatment Designs Watch on What are the disadvantages of alternating treatments? To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Cooper et al. The multiple baseline family of designs includes multiple baseline and multiple probe designs. Smith (2012) found that SCD was reported in 143 different journals that span a variety of fields such as behavior analysis, psychology, education, speech, and pain management; across these fields, multiple baselines account for 69% of SCDs. Single-case designs for educational research. To summarize, the replicated within-tier analysis with sufficient lag can rigorously control for the threat of maturation. With stable data, the range within which future data points will fall is Behavior Therapy, 6(5), 601608. Routledge/Taylor & Francis Group. Nonconcurrent multiple baseline designs are those in which tiers are not synchronized in real time. Research methodologists have identified numerous potential alternative explanations that are threats to internal validity (e.g., Campbell & Stanley, 1963; Cooper et al., 2020; Kazdin, 2021; Shadish et al., 2002). Although the design entails two of the three elements of baseline logicprediction and replicationthe absence of concurrent baseline measures precludes the verification of [the prediction]. This would align the definition with the critical features required to demonstrate experimental control and thereby allow strong causal statements based on multiple baseline designs. We are not pointing to flaws in execution of the design; we are pointing to inherent weaknesses. Part of Springer Nature. Throughout this article we have argued that controlling for the three main threats to internal validitymaturation, testing and session experience, and coincidental eventsin multiple baseline designs requires attention to three distinct dimensions of lag of phase changes across tiers. While the fact that the researcher does not use a large number of participants has its advantages, it also has a downside: Because the experimental trials are run on only one subject, it is difficult to empirically show with the experiment's data that the findings will generalize out to larger populations. (Our specification of phase change offset in terms of real time, days in baseline, and sessions in baseline is unusual. Recommendations for reporting multiple-baseline designs across participants. ), Single case research methodology: Applications in special education and behavioral sciences (pp. Given this dilemma, priority should be given to optimizing the within-tier comparisons because this is the comparison that can confer stronger control. Taplin, P. S., & Reid, J. Journal of Behavioral Education, 13(4), 267276. For example, knowing the date of session 10 in tier 1 tells us nothing about the date of session 10 in tier 2. This assumption was initially identified by Kazdin and Kopel in 1975, but its implications for the rigor of the across-tier comparison have rarely been discussed since that time. Behavior Research Methods, 43(4), 971980. Department of Educational Psychology, Neag School of Education, University of Connecticut, Storrs, CT, 06269, USA, You can also search for this author in Further, it is impossible to know how many events, which events, or the severity of the events that are missed by an across-tier comparison. Nonconcurrent designs are said to be substantially compromised with respect to internal validity and in general this limitation is ascribed to their supposed weakness in addressing threats of coincidental events (i.e., history). It is possible that a coincidental event may be present for all tiers but have different effects on different tiers. However, we can never ensure that any two contexts or any two session times are not subject to unique events during the study. It is interesting that this emphasis on across-tier comparisons is the opposite of that evident in Baer et al. https://doi.org/10.1037/a0029312, Watson, P. J., & Workman, E. A. Three children (ages 4;3 to 5;3) with moderate-severe to severe SSDs participated in two cycles of therapy. This is consistent with the judgements made by numerous existing standards and recommendations (e.g., Gast et al., 2018; Horner et al., 2005; Kazdin, 2021; Kratochwill et al., 2013). To understand the ability of concurrent designs to meet these assumptions we must distinguish different types of coincidental events based on the scope of their effects. Behavioral Interventions, 20(3), 219224. A baseline (A) and an intervention (B) are included in a straightforward AB design psychological experiment (B). https://doi.org/10.1901/jaba.1968.1-91, Article They do not elaborate on the importance of this type of comparison. For example, in a multiple baseline across settings, the settings could present somewhat different demands. Shadish, W. R., Cook, T. D., & Campbell, D. T. (2002). Second, the across-tier comparison assumes that extraneous variables will affect multiple tiers similarly. This comparison can reveal the influence of an extraneous variable only if it causes a change in several tiers at about the same time. The authors discuss two designs commonly used to demonstrate reliable control of an important behavior change (p. 94). For example, a baseline might be et al. Some researchers believe ABAB is a stronger design since it has multiple reversals. Textbook authors, editors, and readers of research should consider nonconcurrent multiple baseline designs to be capable of supporting conclusions every bit as strong as those from concurrent designs. To offer some guidance, we believe that under ideal conditionsadequate lags between phase changes, circumstances that do not suggest that threats are particularly likely, and clear results across tiersthree tiers in a multiple baseline can provide strong control against threats to internal validity. In both within- and across-tier comparisons, the dates on which the sessions took place are not relevant to the effects of testing and session experience. This has at least two effects: first, the multiple baseline is seen as weaker than the withdrawal design because of this dependence on the across-tier analysis; and second, when nonconcurrent multiple baseline designs are introduced years later, their rigor will be understood by many methodologists in terms of control by across-tier comparisons only, without consideration of replicated within-tier comparisons. Further, for both types of multiple baselines, the threat of coincidental events should be evaluated primarily based on replicated within-tier comparisons. In both forms of multiple baseline designs, a potential treatment effect in the first tier would be vulnerable to the threat that the changes in data could be a result of testing or session experience. Using Single-Case Designs in Practical Settings: Is Within-Subject Replication Always Necessary? However, each replication of the possible treatment effect that takes place at a substantially distinct calendar date reduces the plausibility of this threat. This provides clear information about the number of sessions that precede the phase change in each tier, and therefore constitutes a strong basis for controlling the threat of testing and session experience. Routledge/Taylor & Francis Group. It is surprising that there is no single consensus definition of multiple baseline designs. How many tiers do we need? All three of these dimensions of lag are necessary to rigorously control for commonly recognized threats to internal validity and establish experimental control. https://doi.org/10.1002/bin.191, Article Single case experimental designs: Strategies for studying behavior change (3rd ed.). WebIn yet a third version of the multiple-baseline design, multiple baselines are established for the same participant but in different settings. The withdrawal phase of an A-B-A design is important because it shows that the results of the intervention weren't just a result of a difference in time. Features of the target behaviors, participants, measurement, and so forth can make threats to internal validity more or less likely. Finally, we make recommendations for more rigorous use, reporting, and evaluation of multiple baseline designs. The definition states that there must be sufficient lag between phase changesthis is not further specified because the amount of lag necessary to ensure that any single amount of maturation, number of sessions, or coincidental event could not cause changes in multiple tiers must be determined in the context of the particular study. In general, in a concurrent multiple baseline design across any factor, the across-tier analysis is inherently insensitive to coincidental events that are limited to a single tier of that factor. WebWhat are some disadvantages of alternating treatment design? We challenge this assertion. Journal of Consulting & Clinical Psychology, 49(2), 193211. They then describe the multiple baseline technique (p. 94) and two types of comparisons that contribute to its experimental control. WebDisadvantages to Multiple Baseline Designs -Weaker method of showing experimental control than a reversal (b/c no withdrawal of treatment) -Delay in treatment can occur as In a concurrent multiple baseline that involves a single participant across settings, behaviors, antecedent stimuli etc., this kind of event would be expected to contact all tiers. When changes in data occur immediately after the phase change, are large in magnitude, and are consistent across tiers, threats to internal validity tend to be less plausible explanations of the data patterns, and fewer tiers would be required to rule them out. In this highly influential early textbook on SCD, Hersen and Barlow describe only the across-tier analysis and fail to mention replicated within-tier comparisons. PubMed The purposes of this article are to (1) thoroughly examine the impact that threats to internal validity can have on concurrent and nonconcurrent multiple baseline designs; (2) describe the critical features of each design type that control for threats to internal validity; and (3) offer recommendations for use and reporting of concurrent and nonconcurrent multiple baseline designs. We will focus on the three types of threats that are addressed through comparisons between baseline and treatment phases in multiple baseline designs: maturation, testing and session experience, and coincidental events.Footnote 1. If a potential treatment effect is seen in one tier, the researcher cannot refer to data from the same day in an untreated tier because the tiers are not synchronized in real time and may not even overlap in real time. The assumption that all tiers respond similarly to maturation may be somewhat more problematic. Journal of Applied Behavior Analysis, 1(1), 9197. 288335). Remedial and Special Education, 34(1), 2638. Part of Springer Nature. Therefore, concurrent and nonconcurrent designs are virtually identical in control for testing and session experience. PubMed Central However, researchers in clinical, educational, and other applied settings recognized that they could expand research much further if the tiers of a multiple baseline could be conducted as they became available sequentially rather than simultaneously. Journal of Behavioral Education, 13, 267276.
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