8: Selecting, Training, and Addressing the Influence of Interventionists

Selecting, Training, and Addressing the Influence of Interventionists

The terms interventionists, therapists, and providers are used interchangeably, referring to the individuals responsible for delivering health interventions. In general, interventionists are health professionals who have the qualifications required by the respective regulatory organizations that enable them to provide an intervention. In some instances, laypersons assume the responsibility of providing health interventions. Lay persons are usually involved in the implementation of interventions in community settings and aimed at enhancing people’s self‐management of chronic conditions, social connectedness, and/or general health. Nonetheless, the literature focuses on the role and influence of health professionals in delivering interventions, and their influence on the implementation of the intervention.

In this chapter, the role of interventionists is briefly described. Evidence of their influence on the implementation and outcomes of interventions is synthesized. Strategies for selecting and training interventionists are discussed as a means for enhancing their competence for, and promoting fidelity of, intervention delivery. Methodological features for studies aimed at investigating interventionists’ effects are highlighted.


In most, if not all, health interventions, the interventionist is the central figure in their delivery, serving as the medium through which the intervention’s active ingredients are provided to clients. In educational interventions, the interventionist (e.g. health educator, nurse) relays the information on the health problem and on the treatment recommendations to manage the problem to clients. In cognitive‐behavioral interventions, the interventionist (e.g. psychologist) facilitates discussion of the health problem, treatment recommendations to manage it, and ways to address factors that interfere with the implementation of the treatment recommendations in daily life. The interventionist also demonstrates the performance of pertinent cognitive and/or behavioral skills, and assists in monitoring and offers feedback on skill performance. In physical interventions, the interventionist (e.g. physical or occupational therapist) gives instructions on the application of the skills required for applying the treatment recommendations, and provides instrumental support as needed. Even in the delivery of pharmacological interventions, the interventionist (e.g. pharmacist) is involved not only in dispensing the medication, but also in providing information on its effects, dose, and adverse reactions, and in discussing issues of adherence.

Whether health interventions are offered in an individual or group, face‐to‐face, in‐person or technology‐based format, they involve interactions between interventionists and clients. It is through these interactions that interventionists provide, and clients are exposed to the intervention’s components. During these interactions, the interventionist conveys, explains, and clarifies the content, that is, the information and instructions on the treatment recommendations that clients are expected to enact. In addition, the interventionist engages clients in the intervention activities (e.g. discussion, performance of a skill) planned for each session, and carries out the nonspecific components (or respective activities) aimed to support clients in implementing the treatment recommendations. Interventionists are requested to provide the specific and nonspecific components as delineated and detailed in the intervention manual in order to minimize deviations or variations in, and to enhance fidelity of, intervention delivery. As mentioned in Chapter 6, fidelity contributes to the achievement of beneficial outcomes.

Interventionists are individuals who vary in their personal and professional qualities, which may affect their capacity and ability to deliver health interventions with fidelity and competence. Such individuality influences interventionists’ performance in providing the intervention and, consequently, effectiveness in producing beneficial client outcomes.


Conventionally, interventionists’ variability and contribution to the intervention delivery and outcome achievement have often been ignored in intervention research. This is related to the traditional perspective considering the interactions between interventionists and clients as inert, having no influence on the intervention’s effectiveness. Cumulating empirical evidence suggests otherwise, that is, interventionists’ influence is not ignorable; it is on par with the effects of the intervention’s active ingredients (Horvath et al., 2011). This implies that the interventionists’ contribution to outcomes is comparable to the contribution of the intervention’s active ingredients to outcomes, whether the intervention is delivered in research or practice.

8.2.1 Traditional Perspective On Interventionists’ Influence

The traditional perspective informing intervention research acknowledges that the interactions between the interventionist and the clients are the means for delivering the active ingredients of the intervention. It views interventionists as the medium through which the active ingredients are provided; therefore, the interventionists’ role is simply to facilitate the delivery of the intervention. Accordingly, just like other modes for delivering the intervention, interventionists are not expected to vary or differ in the way they provide the intervention, to affect clients’ engagement in the intervention and enactment of the treatment recommendations and to contribute to outcome achievement. In this traditional perspective, only the active ingredients are posited to be responsible for producing the beneficial changes in the outcomes, and all other aspects inherent in the context of intervention delivery including the interventionists are hypothesized to be inert.

The hypothesized inert nature of the interventionist–client interactions forms the basis of the assumption of “interventionist uniformity” that prevailed in intervention research (Kim et al., 2006). The assumption implies that interventionists are equivalent in their ability to deliver the intervention and, hence, to play no (or minimal) role in the achievement of outcomes. Equivalence means that interventionists are comparable in their qualities, capacity, and skills required for providing the intervention, as well as in their actual performance in delivering the intervention. As such, interventionists are considered intersubstitutable; they can be carefully selected and intensively trained in the implementation of the intervention. The training is expected to enhance and equalize their performance in delivering the intervention, which promotes the competence and fidelity with which they provide the intervention. The expectations of equal performance across interventionists and of their limited, if any, contribution to outcomes resulted in little attention given to the examination of interventionists’ influence in intervention research.

Recent experience in intervention evaluation research and in implementation initiatives (aimed at disseminating and integrating interventions in practice) indicates that the assumptions of interventionist uniformity, equal performance, and limited contribution to outcomes are untenable. Cumulating evidence supports the interventionists’ influence on outcomes which should be accounted for in order to enhance the validity of conclusions or inferences regarding the intervention’s effectiveness (Lutz & Barkham, 2015).

8.2.2 Evidence of Interventionist Influence

As mentioned previously, interventionists are individuals who have unique characteristics. They differ in their personal qualities, including their sociodemographic profile; cultural beliefs and values; and interpersonal skills. Interventionists also vary in their professional qualifications such as education, knowledge, theoretical orientation, practical skills, and attitudes toward the health problem, the target population, and treatments. Interventionists’ personal and professional characteristics, in particular beliefs, attitudes, and skills, inform their perspectives on health problems and treatments, as well as their behaviors and interactions with clients.

Clinical practice is replete with examples illustrating differences among health professionals. Differences are reported in the technical and relational aspects of care. Health professionals vary in their clinical knowledge, experience, and expertise, which affect the quality of their treatment decision‐making and performance in providing treatments. Health professionals differ in their communication, interpersonal and interactional skills, which affect their collaboration with members of the healthcare team, and their ability to develop and maintain a rapport, therapeutic relationship, or working alliance with clients. A therapeutic relationship is a nurturing one, in which health professionals and clients trust each other and respect each other’s beliefs and values; exchange information that guides the planning of care; explore pressing concerns and preferences; and participate as equal partners in making treatment decisions as well as in implementing, evaluating, and revising treatment, as needed (Kitson et al., 2013; Sidani & Fox, 2014). A working alliance is a collaborative relationship in which health professionals and clients develop a common understanding and an agreement on the intervention’s goals and tasks (Degnan et al., 2016).

Emerging empirical evidence confirms interventionists’ variability in the delivery and effectiveness of interventions. The evidence has been generated primarily in studies evaluating psychotherapy, with a recent surge in the number of studies that investigated the influence of interventionists providing other health interventions implemented in research or practice. Studies have examined interventionists’ contribution to client outcomes, difference in performance or in the delivery of interventions, and factors predicting their performance and effectiveness. Interventionists’ Contribution to Outcomes

The interventionists’ contribution to outcomes, also referred to as therapist effects, has been investigated in an increasing number of individual studies and systematic reviews/meta‐analyses. The studies used a range of experimental and nonexperimental or naturalistic designs. The interventionists were responsible for delivering specific interventions such as behavioral therapy for depression (e.g. Titzler et al., 2018) in research, or selected evidence‐based therapies (e.g. Becker‐Haimes et al., 2017) in practice. The number of interventionists included in these studies ranged from less than 10 to more than 100; similarly, the client sample size varied across studies, with those involving a naturalistic design having larger samples of interventionists and clients. The client outcomes frequently examined reflected the experience of the health problem targeted by the intervention, and general health or functioning. Despite these differences (i.e. in study design, intervention, sample size, and outcomes), the findings were consistent in showing differences in client outcomes across interventionists; in other words, clients assigned to different interventionists attained different levels of improvement in the outcomes (e.g. Anderson et al., 2009; Dinger et al., 2008; Goldberg et al., 2018). It has been estimated, in individual studies and meta‐analyses, that interventionists account for 3–13.5% of the variance in client outcomes observed following treatment (e.g. Baldwin & Imel, 2013; Del Re et al., 2012; Elkin et al., 2006; Lutz et al., 2007; Saxon et al., 2017; Schiefele et al., 2017; Zimmermann et al., 2017). It is important to note that the amount of variance in client outcomes accounted for by interventionists is equal (Horvath et al., 2011) or larger than the amount of variance in the outcomes explained by the intervention that the clients received; the latter variance ranged between 0 and 2% (Kim et al., 2006; Wampold & Brown, 2005).

Recognizing that achievement of desired outcomes rests on clients’ completion of treatment (which may be associated with interventionists’ performance), researchers have also investigated client attrition rates across interventionists. In two recent naturalistic studies, differences in the rates of clients’ withdrawal from treatment were examined for therapists providing different types of psychotherapy. The results were comparable, showing that the treatment attrition or withdrawal rates varied across therapists. The attrition rates ranged between 1.2 and 73.2% (Saxon et al., 2017), whereas the therapist effects accounted for 6% of the variance in the attrition rates after controlling for other client characteristics known to be associated with attrition such as initial or pre‐treatment severity of the health problem (Zimmermann et al., 2017).

Variability in interventionists’ contribution to clients’ attrition and outcomes underscores the importance of attending to the interventionists’ influence or effect in intervention evaluation research. Realizing the interventionists’ effects may be attributed to the manner in which they provide treatment, studies were designed to explore interventionists’ performance in delivering health interventions and factors that predict their performance and effectiveness. Interventionists’ Performance in Intervention Delivery

Two aspects of interventionists’ performance have been examined: (1) fidelity of intervention delivery, which was operationalized in adherence to the intervention manual (comparable to the technical aspect of care), and (2) ability to build a rapport, therapeutic relationship, or working alliance with clients during intervention delivery, which is often considered as reflecting interventionists’ competence (also referred to as common factors, and comparable to the relational aspect of care). Variability was observed in the extent to which interventionists adhered to the intervention in research and practice (e.g. Imel et al., 2011).

Evidence showed that health professionals’ levels of adherence to different evidence‐based psychotherapies were lower than the level considered acceptable, which is ≥80% (Reichow et al., 2008). Levels of adherence ranged between 4.2 and 27.8% in one study (Tschuschke et al., 2015), and from 6.6 to 90% with a mean of 30% in another study (Verschuur et al., 2019). Detailed analyses showed that levels of adherence differed not only across health professionals but also across clients receiving treatment from the same health professional, across types of psychotherapy, and across sessions of the same therapy (Tschuschke et al., 2015). Similarly, the working alliance was found to consistently vary across interventionists, clients presenting with different health problems, and types of interventions (e.g. Imel et al., 2011; Moyers et al., 2005; Wampold & Imel, 2015). Factors Predicting Interventionists’ Performance

Several personal factors have been investigated in an attempt to understand what contributes to the variability in interventionists’ performance in delivering health interventions. Results of individual studies indicated that interventionists who displayed high levels of adherence were likely to have high levels of education (Campbell et al., 2013); to report high self‐efficacy in skills for implementing the intervention components (Campbell et al., 2013); and to perceive the intervention favorably, that is, acceptable, advantageous, and consistent with their theoretical orientation and with their clinical experiences (Borrelli, 2011; McDiamid Nelson et al., 2012; Titzler et al., 2018). There were mixed findings related to interventionists’ experience. Experience was not associated with adherence in one study (Mauricio et al., 2019), whereas interventionists with low experience (≤ 5 years) exhibited high levels of adherence (Campbell et al., 2013; McDiamid Nelson et al., 2012). This evidence suggests that interventionists with graduate education may have been exposed to different interventions and had ample opportunities to learn and apply the interventions throughout their educational program, which enhances their comfort and confidence in their skills.

One recent study examined the association of selected personal factors with interventionists’ working alliance. One such factor included attachment style and the results suggested that interventionists with attachment security had high level of alliance (Degnan et al., 2016). Factors Predicting Interventionists’ Effectiveness

Researchers attempted to gain an understanding of the observed interventionists’ influence on client outcomes by examining the extent to which interventionists’ characteristics and performance were related to client outcomes. The interventionists’ characteristics entailed their personal attributes (age, gender) and professional qualifications (education, years of experience, theoretical or treatment orientation) and qualities (empathy). In general, the results were mixed. Whereas earlier studies found nonsignificant associations of interventionists’ characteristics with client outcomes (e.g. Dinger et al., 2008; Okiishi et al., 2003; Wampold & Brown, 2005), more recent ones reported the following:

  1. Young interventionists had better client outcomes (Berghout & Zevalkink, 2011).
  2. Female interventionists had better outcomes, after controlling for caseload (Berghout & Zevalkink, 2011).
  3. Interventionists’ years of experience and theoretical orientation were not associated with clients’ outcomes (Berghout & Zevalkink, 2011; Huppert et al., 2001).

Furthermore, Saxon et al. (2017) found that clients who perceived their interventionists as having no or low empathy were likely to withdraw from treatment.

The contribution of interventionists’ performance, including adherence to the intervention manual and competence (or working alliance) in providing treatment, has been examined in individual studies, systematic reviews, or meta‐analyses. The results pertaining to the association between interventionists’ adherence and clients’ outcomes were inconsistent. For instance, Tschuschke et al. (2015) reported that adherence alone did not predict outcomes. Other researchers found that increased adherence is associated with better outcomes (DiGennaro Reed & Codding 2014; Pellecchia et al., 2015; Schoenwald et al., 2011). Evidence from Webb et al.’s (2010) meta‐analysis suggests that the effect of adherence on outcomes was small (average effect size: 0.02). This small effect was theoretically unexpected and could be attributed to methodological factors such as differences in the methods used to collect data on adherence, the unreliability of the measures, restricted range (i.e. high levels of adherence), or nonlinear nature of the relationship. Indeed, Barber et al. (2006) observed a curvilinear relationship whereby high and low levels of adherence were associated with poor client outcomes. It appears that a moderate level of adherence is optimal for interventionists’ effectiveness. This point reflects interventionists’ perception of the importance of providing treatment while being responsive to clients’ individual concerns and life circumstance (i.e. adapting interventions). Interventionists’ responsiveness may be an essential element of their competence.

The findings pertaining to the contribution of interventionists’ competence, operationalized in therapeutic relationship, interpersonal skills, or working alliance, to client outcomes are consistent in supporting its direct effects on outcomes. Evidence synthesized across individual studies and systematic reviews or meta‐analyses shows that the way in which interventionists deliver health interventions predicts client outcomes. In particular, the working alliance between interventionists and clients (1) enhances clients’ appreciation of the value of the intervention, satisfaction with treatment, and motivation to carry out and adhere to the treatment recommendations (Constantino et al., 2007; Fuertes et al., 2007); (2) is associated with reduced rates of withdrawal from treatment (Alcázar Olán et al., 2010); (3) is positively related with achievement of beneficial client outcomes (Del Re et al., 2012; Dinger et al., 2008; Krukowski et al., 2019). The effects of working alliance on client outcomes were of a small‐to‐moderate (range: 0.02 to 0.27) size, as estimated in meta‐analyses (Cameron et al., 2018; Castonguay et al., 2006; Horvath et al., 2011; Webb et al., 2010). On average, the working alliance accounted for 8% of the variability in the outcome (Horvath et al., 2011), which was higher than the percentage of outcome variance attributable to the intervention’s effects (Kaplowitz et al., 2011).

The contribution of the interventionists’ interpersonal skills to client outcomes has been recently investigated. Facilitative interpersonal skills, which are the cornerstone of the therapeutic relationship or working alliance, include: verbal fluency, warmth, empathy, persuasiveness, hopefulness, ability to create an accepting and supportive relationship, and being problem‐focused (Anderson et al., 2009; Lingiardi et al., 2018). Evidence indicates that interventionists exhibiting these facilitative interpersonal skills were effective in increasing clients’ engagement in treatment (Moyers et al., 2005; Tschuschke et al., 2015) and in improving clients’ outcomes (Anderson et al., 2009; Berghout & Zevalkink, 2011; Goldberg et al., 2018; Greeson et al., 2009; Gaume et al., 2009; Lingiardi et al., 2018).

Mounting clinical and empirical evidence converge in supporting the interventionists’ influence on the delivery and outcomes of health interventions. Interventionists’ performance including their level of adherence to the intervention manual, and competence represented in their interpersonal skills and working alliance, more so than their personal characteristics, are significant predictors of client outcomes. It appears that interventionists’ performance and competence are more influential than the active ingredients of interventions in accounting for the benefits of treatments (Kaplowitz et al., 2011). Accordingly, it would be useful to carefully select and train interventionists, monitor their performance (discussed in Chapter 9), and investigate their contribution to outcomes in intervention evaluation studies.


The mounting evidence on the interventionists’ influence points to the importance of carefully considering the interventionists’ characteristics when selecting them into their role in research or practice. The recommendation is to select interventionists who have the personal and professional qualities known to contribute to their performance and effectiveness, without violating local human resources policies. The general intent is to hire the most competent interventionists, capable of delivering the intervention with fidelity while building a good working alliance with clients. No guidelines are available to inform the selection of interventionists. Following are suggestions for qualities to consider and for strategies to ascertain them.

8.3.1 Interventionists’ Qualities

It may not be possible to list all qualities considered important for delivering specific health interventions. However, the following is a list of general personal and professional characteristics, generated from empirical and experiential evidence, to be taken into account when selecting interventionists, as also suggested by Borrelli (2011). Personal Characteristics

Whereas recent evidence indicates that interventionists’ sociodemographic characteristics do not influence their performance and effectiveness as much as their personal attributes, it may be useful to consider both categories in some instances.

  1. Sociodemographic characteristics: These include (but are not limited to) age, gender, and ethnicity. Congruence on these characteristics between interventionists and clients may facilitate the delivery of interventions addressing sensitive topics. For instance, women feel comfortable discussing topics related to sexuality or breastfeeding with female interventionists; persons of a particular culture are at ease expressing their beliefs about the health problem and its treatment (which may affect their enactment of the treatment recommendations) with an interventionist of the same culture (who can understand and appreciate their values and beliefs).
  2. Personal attributes: These relate to general personality style and relational or interpersonal skills. Examples of personality style are: extroversion, humor, attachment, reflective and introspective capacities (Degnan et al., 2016; Lingiardi et al., 2018). Interpersonal skills are illustrated with interventionists demonstrating: warmth, empathy, helpfulness, hopefulness, verbal fluency, and persuasiveness (Anderson et al., 2009

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Nov 28, 2021 | Posted by in NURSING | Comments Off on 8: Selecting, Training, and Addressing the Influence of Interventionists
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