Tailoring cognitive behavioural therapy for insomnia across contexts, conditions, and individuals: What do we know, where do we go?

Cognitive behavioural therapy for insomnia (CBT‐I) is considered the front‐line treatment for insomnia. Despite the demonstrated effectiveness of CBT‐I, it is necessary to consider how CBT‐I may be tailored to different individuals. The purpose of the present review is to provide a summary of literature on tailoring CBT‐I to different individuals and provide directions for future research. This review focused on the following domains of adaptation: (i) tailoring CBT‐I components to individuals with comorbid mental or physical health conditions such as comorbid depression and pain; (ii) adapting CBT‐I delivery for different contexts in which individuals exist, such as inpatient, educational, and different social/cultural settings, (iii) adapting CBT‐I to specific individuals via case‐formulation in clinical settings. We highlight current gaps in the exploration of tailored CBT‐I, including a lack of research methodology to evaluate tailored interventions, a need for the integration of ongoing individualised assessment to inform treatment, and the necessary involvement of consumers and stakeholders throughout the research and treatment development process. Together, this review showed abundant adaptations in CBT‐I already exist in the literature. Future research is needed in understanding when and how to apply adaptations in CBT‐I and evaluate the benefits of these adaptations.

constellation of symptoms (American Psychiatric Association, 2013;World Health Organization, 2019).However, there are large individual differences in symptom presentation (Benjamins et al., 2017) and the contexts in which these symptoms occur.When considering sleep across the life span, for example, sleep initiation difficulties are common in young adults and adolescents (Gradisar et al., 2011), whilst difficulties in sleep maintenance are common in older adults (Fiorentino & Martin, 2010).Cultural and social factors may also contribute to insomnia presentation; e.g., traditional health beliefs may influence the interpretation of insomnia symptoms in some Asian countries (Lee, 1995;Yung et al., 2016).Further, co-existing physical and mental health conditions could influence the presentation of insomnia (Wu et al., 2015;Zhou et al., 2020).Therefore, insomnia exists in unique contexts for each individual, with varying factors contributing to the presentation of insomnia and responses to treatment.
In this paper, we will discuss current literature and potential gaps for future research in how CBT-I is adapted to individuals' contexts and needs.The present review provides a summary of literature that have utilised adaptation methods for CBT-I, we then present a summary of gaps in current evidence and suggestions for future directions.

| EXISTING RESEARCH ON CBT-I ADAPTATIONS
Existing research typically adapted and tested CBT-I to meet the needs of individuals who may share a common characteristic, such as having a mental or physical health condition that co-exists with insomnia, or sharing a common context or environment (e.g., hospital, school, household).Although these adaptations were condition and context focused, rather than individual focused, they provide valuable insight into how CBT-I could be adapted in varying situations.In summarising findings, we reviewed studies that included at least one of the following CBT-I components: stimulus control, sleep restriction, and cognitive therapy.

| Condition-focused adaptation
With the increasing recognition of comorbid insomnia (Lichstein, 2006), some trials have focused on adapting CBT-I to situations where insomnia co-exists with another physical or mental health condition.This section reviews adaptations made to core components of CBT-I when delivered in individuals with different co-existing conditions.

| Stimulus control
Physical limitations such as mobility, vestibular issues, as well as severe psychiatric symptoms can make it challenging or even unsafe to get out of bed or leave the bedroom when unable to fall asleep (Haynes et al., 2011;Martin et al., 2017;Sheaves et al., 2018a;Tang et al., 2020).Stimulus control has been adapted by allowing individuals to either move to a chair within their sleeping environment or sit up in bed for relaxing activities (Martin et al., 2017;Sheaves et al., 2018b).Similarly, the instruction to only go to bed when sleepy has been replaced with a circadian-derived time for people with bipolar disorders (Harvey et al., 2015) who may have difficulty becoming aware of sleepiness.
Individuals may spend too little or too much time in bed (TIB) due to comorbid conditions.Where periods of rest but not daytime sleep are necessary, such as in individuals with fatigue after cancer (Zhou et al., 2017) and traumatic brain injury (Nguyen et al., 2017), emphasis was placed on identifying alternative places to rest outside of the primary sleeping location.Goal setting and activity scheduling were used in conjunction with stimulus control to reinforce the benefits of reducing TIB in depression (Sadler et al., 2018;Scogin et al., 2018) and getting out of bed in bipolar disorders (Harvey et al., 2015;Kaplan et al., 2018).When sleep or spending TIB is used to avoid delusions or hallucinations in psychotic disorders, it may be necessary to identify alternative coping strategies or safe location (Freeman et al., 2015;Waite et al., 2016).Conversely, fear of bed from distressing psychotic or traumatic experiences can substantially interfere with associating bed with sleep (Freeman et al., 2015;Waite et al., 2016).Cognitive therapy can be provided prior to stimulus control to reduce distress and support coping (Conroy et al., 2019;Waite et al., 2016).

| Sleep restriction
Adaptations are often made to mitigate adverse effects of sleep restriction therapy (SRT), such as waketime sleepiness, fatigue, and reduced motivation (Kyle et al., 2011).One common modification is to TIB recommendations.In perinatal insomnia, 30 min were added to the typically recommended average total sleep time for initial TIB, and TIB windows were never shorter than 5.5 h (Manber et al., 2019(Manber et al., , 2023)).A minimum of 5.5 h was also used in a trial of CBT-I within a comorbid insomnia and sleep apnoea sample, with the initial TIB further modified for each individual based on baseline waketime sleepiness (Sweetman et al., 2019).Similarly, a 6.5 h minimum TIB was used to reduce the risk of sleep deprivation triggering a manic or hypomanic episode in bipolar disorders (Harvey et al., 2015;Kaplan et al., 2018).To account for shift work-related sleep debt, an additional hour of TIB for up to three sleep periods in individuals with shift work disorder was allowed (Järnefelt et al., 2020).In patients with cardiovascular disease, sleep restriction was limited to 1-2 nights/week initially, then gradually increased (Siebmanns et al., 2021).
When standard SRT cannot be tolerated, it has been substituted for, or used in combination with sleep compression therapy, where TIB is restricted gradually by 15-30 min each week to achieve a desired sleep efficiency.Sleep compression was used in older adults with depression (Scogin et al., 2018), mild cognitive impairment (Cassidy-Eagle et al., 2018), and other comorbid conditions (Martin et al., 2017).
In some conditions, SRT was omitted, such as schizophrenia (Waite et al., 2016), subthreshold psychosis (Bradley et al., 2018), and pregnancy (Cain et al., 2020).Instead, alternatives to improving sleep efficiency were used, such as establishing regular sleep and wake times in depressive and bipolar disorders (Conroy et al., 2019;Harvey et al., 2015) and fixed pre-bed routines in psychiatric inpatients (Crönlein et al., 2019).
Other adaptations to SRT have included providing alternate coping strategies for sleepiness in individuals with substance use disorders (Haynes et al., 2011), consultation with treating psychiatrists for safety planning in bipolar disorders (Harvey et al., 2015;Steinan et al., 2014), and promoting adherence by using alarms and reminders in cognitive impairment (Cassidy-Eagle et al., 2018) and psychosis (Bradley et al., 2018).

| Cognitive therapy
Adaptations to standard CBT-I cognitive components have focused on incorporating commonly used cognitive techniques from the treatments of comorbid conditions.Cognitive components have been expanded to address concerns related to the comorbid condition that may interfere with sleep, such as worries about relapse in substance use disorders (Arnedt et al., 2011(Arnedt et al., , 2023)), pain catastrophising in fibromyalgia (Martínez et al., 2014), controllable and uncontrollable factors in pregnancy (MacKinnon et al., 2021), unhelpful beliefs about rest versus sleep in traumatic brain injury (Nguyen et al., 2017), coping with daytime fatigue in depression (Carney et al., 2017), and sleepwake state perception in bipolar disorders (Steinan et al., 2014).To address these cognitions, elements from CBT for chronic pain (McCrae et al., 2019;Pigeon et al., 2012;Tang et al., 2020), depression (Scogin et al., 2018), psychosis (Waite et al., 2016), and alcohol and substance use disorders (Arnedt et al., 2023) were provided alongside sleep-focused cognitive therapy.
Given the unique features of some comorbid conditions, non-CBT-I strategies have also been incorporated.Motivational interviewing was applied for goal setting, enhancing motivation for change in comorbid bipolar disorder (Harvey et al., 2015) and delayed sleepwake phase disorder in adolescents (Danielsson et al., 2016).Behavioural activation was used to facilitate engagement in treatment for adolescents with depression (Conroy et al., 2019).Image rehearsal therapy, nightmare re-scripting, and grounding techniques were used alongside CBT-I to manage nightmares in veterans with co-occurring insomnia and post-traumatic stress disorder (Germain et al., 2012;Harb et al., 2019;Laurel Franklin et al., 2018;Margolies et al., 2013), school-aged children with autism spectrum disorder (McCrae et al., 2020), and adults with schizophrenia (Waite et al., 2016).
Graded exposure to bed was used to manage fears from distressing psychotic or traumatic experiences in schizophrenia (Waite et al., 2016).Paradoxical intention was used to reduce sleep effort, hyperarousal, and sleep-related anxiety in individuals with persistent persecutory delusions (Waite et al., 2016).

| Sleep hygiene
Sleep hygiene typically includes components that support regular sleep-wake times and reduce external sleep-interfering factors.To regularise sleep-wake times and social routines in bipolar disorders, principles of interpersonal social rhythms therapy have been incorporated into CBT-I (Harvey et al., 2015;Kaplan et al., 2018); e.g., collaboratively developed wind-down and wake-up routines that incorporated appropriately timed light/dark exposure, meals, exercise, and other activities.A focus on developing bedtime and wake-up routines has also been implemented for other comorbid conditions, such as cancer recovery (Quesnel et al., 2003), traumatic brain injury (Moore et al., 2021), schizophrenia (Chiu et al., 2018;Waite et al., 2016), and other comorbid psychiatric disorders (Sheaves et al., 2018a(Sheaves et al., , 2018b)).
Non-CBT-I components have also sometimes been added to support sleep-wake times.Bright light therapy was used in conjunction with CBT-I when treating individuals with comorbid circadian disorders (Gradisar et al., 2011;Peter et al., 2019), bipolar disorders (Harvey et al., 2015;Kaplan et al., 2018;Steinan et al., 2014), and substance use disorders (Britton et al., 2010).Tools such as blue lightfiltering glasses (Janku ˚et al., 2020) or eye masks and earplugs for individuals with shift work disorder (Järnefelt et al., 2020) have been used to help manage unavoidable environmental light exposure.Adjustments to sleeping environment were made for people with schizophrenia (Waite et al., 2016).CBT-I has also been augmented with an exercise training programme for people with comorbid OSA (Cammalleri et al., 2023).

| Sleep education
Sleep education is typically augmented by adding information pertinent to the comorbid conditions, such as the insomnia-maintaining role of conditioned hyperarousal in cancer survivors (Quesnel et al., 2003) and chronic pain (Edinger et al., 2005;Martínez et al., 2014;McCrae et al., 2019), the impacts of excessive fatigue in traumatic brain injury (Nguyen et al., 2017), the risks associated with excessive waketime sleepiness in OSA or shift work disorder (Crawford et al., 2016;Järnefelt et al., 2020), or the effects of substances/medications (Arnedt et al., 2011(Arnedt et al., , 2023;;Currie et al., 2004) or treatments for comorbid conditions (Zhou et al., 2017) on sleep.
Collectively, these condition-focused CBT-I adaptations highlight the breadth of approaches that have been utilised to provide recommendations that are relevant to co-existing conditions, and have implications for individuals' engagement and adherence to CBT-I.

| Context-focused adaptation
This section focuses on studies that adapted CBT-I based on the environment or contexts in which individuals exist to increase CBT-I's access, effectiveness, or integration with existing care.

| Primary care and community settings
When delivering CBT-I in primary care settings, adaptations have been made to address barriers such as provider knowledge, time and resources constraints, and access to ongoing support (Haycock et al., 2021).Examples of modifications include: didactic and manualised CBT-I delivered by non-specialist practitioners (e.g., nurses with brief training) to small groups (Bothelius et al., 2013;Espie et al., 2001Espie et al., , 2014)), utilising weekly general practitioner (GP) consultations to support self-help CBT-I (Katofsky et al., 2012), and using scripts and a sleep restriction algorithm to support GPs in delivering CBT-I over two consultations (Falloon et al., 2015).Given high rates of hypnotic prescription, some studies included hypnotic tapering in addition to a standard CBT-I protocol (Bothelius et al., 2013;Espie et al., 2001).
When delivering CBT-I in community spaces, modifications were made to maximise audience and access.For example, Swift et al.

| Inpatient care
Treating insomnia within inpatient care requires integrated care that effectively uses hospital resources, whilst being tailored to an individual's comorbid conditions and care needs.Core behavioural components, such as sleep restriction and stimulus control, need to be adapted to consider physical limitations during the hospital stay (Crönlein et al., 2019;Sheaves et al., 2018a).Other methods to improve sleep efficiency such as fixed bed and waketimes, strategically scheduling exercise and daytime activities to increase arousal, or using relaxing music to wind-down in the evening have been used in some inpatient settings (Crönlein et al., 2019(Crönlein et al., , 2020;;De Niet et al., 2010;Sheaves et al., 2018a).On inpatient wards, nurses supported adherence to stimulus control (De Niet et al., 2010) and for patients who were unable to leave their rooms or get out of bed, alternative places were provided to sit (e.g., a beanbag) or they were instead advised to sit up in bed when they were unable to sleep (Sheaves et al., 2018a).
Inpatients may face environmental challenges to sleep, such as unfamiliar sleep setting, noise, limited activity, and disrupted routines.
To increase activity and minimise circadian disruption for inpatients, studies have scheduled day activities that promoted wakefulness and enhanced natural light exposure (Crönlein et al., 2020;Sheaves et al., 2018aSheaves et al., , 2018b)).Light therapy boxes were used where some inpatients were unable to go outdoors (Sheaves et al., 2018a(Sheaves et al., , 2018b)).
Routines focused on the timing of meals, activity, light and dark exposure, as well as using relaxation techniques to promote sleep and wakefulness at appropriate times have also been addressed in these settings (Sheaves et al., 2018a(Sheaves et al., , 2018b)).
In terms of format, CBT-I has been delivered by trained nurses and psychologists to inpatients individually (Sheaves et al., 2018a(Sheaves et al., , 2018b)), in groups (Crönlein et al., 2014;Haynes et al., 2011;Hsu et al., 2015), a combination of group and individual sessions (Crönlein et al., 2019), or via video-based lessons (Brock et al., 2018).Sheaves et al. (2018a) provided individually tailored sessions to a small number of patients with psychiatric symptoms that provided significant barriers to engaging in CBT-I.Whilst group-based CBT-I allows individuals to share experiences with other inpatients (Sandlund et al., 2018), the amount of group content received may be limited by the timing and duration of hospital stay.Haynes et al. (2011) remediate this by repeating group CBT-I in 4-week cycles, whereas Crönlein et al. (2014Crönlein et al. ( , 2019Crönlein et al. ( , 2020) used a shorter 2-week programme.
Collectively, the above studies highlight ways the challenges and constraints of an inpatient setting can be overcome with adapted CBT-I.

| Schools
In adapting CBT-I to school-aged children and adolescents, sessions were typically group based with varying degrees of parental involvement, depending on developmental stages.Some researchers have used a combination of child and parent-child sessions in-person (Byrne et al., 2020;Orchard et al., 2020;Schlarb et al., 2010Schlarb et al., , 2018) ) or digitally (Schlarb et al., 2020); some did not directly involve parents, and used motivational interviewing to identifying reasons for and barriers to change (Bei et al., 2013;Blake et al., 2017); some incorporated parents as outside-session support to promote adherence (de Bruin et al., 2014;Paine & Gradisar, 2011); others focused on parents without directly working with their children and incorporated CBT-I components into parenting intervention strategies (Khor et al., 2021).
A few studies showed that it is feasible to deliver CBT-I within the school context Moseley and Gradisar (2009) provided an in-class sleep intervention over 4 weeks to 15-16-year-old adolescents, integrated into the existing school curriculum.In an open pilot, a multicomponent CBT-I intervention was delivered with school psychologists as a weekly after-school group programme to 13-15-year-old adolescents with sleep problems (Bei et al., 2013), showing meaningful reduction in sleep problems and a 90% completion rate.
Age and context-appropriate modifications have also been made.

| Family and household
Interpersonal factors and systems play significant roles in the development and maintenance of insomnia (Rogojanski et al., 2013;Tikotzky & Sadeh, 2010).This section describes research that adapted CBT-I to incorporate members of the individual's social circle to support sustainable behavioural change.Such efforts may be particularly critical, given a recent systematic review that identified social support as one of the few consistent predictors of adherence to CBT-I recommendations (Mellor et al., 2022).
Approximately 60% of adults share their bed with a partner (De Vaus, 2004;National Sleep Foundation, 2012).Those partners are well positioned to support implementation of at-home CBT-I recommendations.Recent efforts adapted CBT-I to incorporate bed partners in all aspects of the treatment, including joint sessions, involving them in problem-solving and treatment-related decision making, collaboratively establishing how to support the client, and empowering both to implement at-home recommendations (Mellor et al., 2019).Adults may also benefit from having other individuals in or outside of the household involved in CBT-I treatment.Kaplan et al. (2018) incorporated calling family/friends or conversing with household members as part of a wake-up routine for adults with bipolar disorders.A qualitative study of CBT-I in comorbid depression identified that active support from relatives and an ongoing focus on adherence throughout were necessary to increase treatment acceptability (Dyrberg et al., 2021).
Family involvement was widely incorporated when treating children and adolescents (Byrne et al., 2020;de Bruin et al., 2014;Orchard et al., 2020;Paine & Gradisar, 2011;Palermo et al., 2016;Schlarb et al., 2010Schlarb et al., , 2018Schlarb et al., , 2020)).Broadly, there has been a focus on increasing engagement and adherence from both parents and adolescents through collaborative goal setting, problem solving, and supporting the implementation of recommendations.Some studies have focused on identifying and changing family habits that maintain poor sleep (Orchard et al., 2020).Bradley et al. (2018) encouraged adolescents at-risk of psychosis to recruit a team of family, friends, or partners to help them implement CBT-I recommendations at home.

| Cultural contexts
Emerging evidence points to the need for adaptation of CBT-I in different cultural contexts.Higher rates of dropout from digital CBT-I have been reported in non-White racial groups in the United States compared to White (Cheng et al., 2019).Two other United States' studies reported Black participants completed fewer sessions and were 1.53-4.10times more likely to prematurely discontinue digital CBT-I than White participants (Kalmbach et al., 2023;Ruprich et al., 2023).All three studies identified significantly greater insomnia severity following treatment in non-White participants (Cheng et al., 2019;Kalmbach et al., 2023;Ruprich et al., 2023).In addition to lower treatment completion rates, Syrian refugees living in Australia identified thoughts related to refugee experiences prior to and following immigration, especially those occurring in the pre-sleep period as significant contributors to sleep difficulties, suggesting the need for tailoring of the cognitive components of CBT-I (Lies et al., 2021).
A few studies have utilised cultural adaptations to CBT-I.In a randomised controlled trial (RCT), Zhou et al. (2022) adapted a digital CBT-I app (SHUTi) for Black American women (SHUTi-BWHS) with insomnia.Visual and didactic content were adapted to include only Black American men and women, with content delivered by Black American physicians.Intervention content was modified for social and cultural contexts, such as implementing stimulus control in noisy neighbourhoods and crowded living environments.The study found that both versions of SHUTi were effective, but SHUTi-BWHS had greater engagement and higher completion rates, which was associated with greater improvements in sleep.In a pilot, Birling et al. (2018) modified the format and content of CBT-I for Chinese patients by interweaving group and individual sessions: group sessions utilised social norms of collective commitment in Chinese culture to increase engagement and motivation, whilst individual sessions addressed specific personal challenges; the study also modified dialogues to align with Chinese cultural values and Chinese Buddhist breathing meditation was used.CBT-I has also been delivered effectively to an ethnically diverse sample of women in the perinatal period (Manber et al., 2019(Manber et al., , 2023) )

| INDIVIDUAL-FOCUSED ADAPTATION
Previously reviewed studies adapted CBT-I for groups of individuals based on shared characteristics such as common contexts, environments, and comorbid conditions.Individual-focused adaptation commonly occur outside of clinical trials and in real-world clinical practice.
CBT-I strategies tested in RCTs have been disseminated amongst sleep medicine practitioners and used in routine practices worldwide (Manber & Carney, 2015).However, outside the context of manualised group CBT-I programmes (Bei et al., 2015;Ong et al., 2008), little is known about how CBT-I is applied in routine clinical practice, in which most services are provided in individual sessions.For example, there is little documented research on the types of component(s) delivered, the sequence of components, intensity of treatment (e.g., number of sessions, frequency of sessions, treatment duration), the practitioners' levels of CBT-I training, and importantly, how these aspects of CBT-I delivery are tailored by clinicians to meet individual patients' needs (Morin et al., 2023).
Evidence-based practice requires clinicians to integrate the best available research with clinical expertise in the context of patient characteristics, culture, and preferences (Evidence-Based Practice in Psychology, 2006), and includes three core components (Lilienfeld et al., 2013): (i) identifying and using the best available evidence, including efficacy studies in research settings, effectiveness studies in real-world settings, and observational research; (ii) clinical skills and experience, which is argued to be necessary for decision making, as "data simply are not available to dictate every decision" (Lilienfeld et al., 2013, p. 886); and (iii) clinicians' knowledge of client values and preferences.
In evidence-based practice, a core process in incorporating evidence into individual treatments is case formulation.During case formulation, the clinician identifies characteristics of the individual case to integrate with relevant theoretical models and selects targets to apply evidence-based treatment.A case formulation approach to CBT-I is widely used in clinical practice (Manber & Carney, 2015).
In this approach, a clinician first assesses a wide range of factors, including but not limited to, current and past sleep-related complaints, sleep-related behaviours and cognitions, chronotype, psychosocial and environmental context of the case, and co-existing mental and physical health conditions.The clinician then integrates these biopsycho-social factors gathered during the initial assessment to formulate a series of working hypotheses using the '4P' model (Perlis et al., 2005) Methodologies other than traditional RCTs may address these gaps.One approach is adaptive trials (Pallmann et al., 2018), which typically use multiple arms, interim analyses, and pre-specified rules to modify aspects of the trial (e.g., intervention configuration) based on acquired data (e.g., treatment responses).Adaptive trials have rarely been applied in the CBT-I literature.One study used a sequential multiple assignment randomized trial (SMART; a type of adaptive trial) to examine the comparative efficacy of different treatment sequences involving psychological and medication therapies for insomnia (Morin et al., 2020).Such studies offer examples of how varying configurations of CBT-I may be assessed systematically for comparative efficacy to inform practice.
Another potential method for assessing adaptation of CBT-I is n-of-1 trials (Lillie et al., 2011), which utilise repeated, randomised comparisons of different intervention configurations within a single individual (Lillie et al., 2011).N-of-1 trials may help identify optimal configuration of CBT-I for individuals based on their treatment responses and preferences; it may be particularly suitable for components of CBT-I as numerous components (e.g., SRT, relaxation, nap avoidance) are typically associated with rapid and measurable treatment responses.In the context of a case formulation approach of individualised CBT-I, n-of-1 trials may provide opportunity for establishing empirical support.
Further, recent development of sleep-measuring wearables sees these devices increasingly integrated into sleep interventions (Glazer Baron et al., 2022).For example, one study provided regular feedback on wearable-measured sleep for individuals with insomnia (Spina et al., 2023), and another added wearable-enabled sleep data synchronisation to a digital behavioural therapy to demonstrate greater engagement and improvements in sleep (Aji et al., 2022).Real-world sleep-wake patterns from wearable devices have also been implemented to recommend personalised sleep schedules to maximise alertness (Song et al., 2023).Personal technologies could play important roles in the development, delivery, and innovations of individualised insomnia treatments (e.g., Murray et al., 2023), particularly with refinement of how to leverage wearable technologies to improve treatments, optimise patient engagement, and reduce barriers to interventions (Glazer Baron et al., 2022).
Finally, tailoring interventions requires the involvement of consumers and stakeholders, who are increasingly included as part of research teams, from conception, design, and testing to implementation (National Health and Medical Research Council, 2016).Although numerous CBT-I trials included focus groups or consumer consultations in early stage of intervention testing (Beattie et al., 2023;Tang et al., 2020;Verma et al., 2020;Zhou et al., 2022), few studies involved consumers and stakeholders systematically throughout all stages of the research process.Future CBT-I research on tailoring the intervention would benefit from collaborating with lived experience researchers and implementation scientists in adopting validated frameworks in involving consumers and stakeholders (Banfield et al., 2018).

| CONCLUSION
Cognitive behavioural therapy for insomnia is firmly established as the front-line intervention for insomnia disorder given its demonstrated efficacy and effectiveness (Cunnington et al., 2013;Qaseem et al., 2016;Riemann et al., 2017).Nonetheless, not everyone who receives the intervention responds sufficiently or completes a course of treatment.This suggests the need to identify those situations in which some adaptation of CBT-I might lead to even more robust outcomes.Thus, consistent with current practice within the field, some degree of personalisation of the intervention is inherent in applying the four-factor model and using the case formulation approach with a given individual.A large number of potential adaptations have been reported in the literature, many of which show promising effects.The critical next steps for the field are to establish a set of evidence-based adaptations more strongly and develop and test practice parameters for when and how to apply those adaptations.

(
2012) recruited 75 people with self-referred sleep problems for a full-day CBT-I workshop plus a booster session at a community centre; regular breaks and brightly coloured slides were used to minimise fatigue.Cape et al. (2016) provided small groups (five-15 people) manualised CBT-I sessions delivered by trainee clinicians at local health centres, libraries, or town-halls.Fuller et al. (2016) modified brief behavioural treatment for insomnia (Buysse et al., 2011) to be delivered in pharmacies by a trained pharmacist over three visits; this study utilised pharmacies' access to individuals seeking sleeping aids to provide access to CBT-I as a non-pharmacological alternative.
with treatment provided in either English or Spanish based on preference.Finally, Scogin et al. (2018) provided CBT-I via telehealth to rural older adults with a large proportion of African American participants; all psychotherapists received a cultural sensitivity workshop to incorporate sociocultural strategies and cultural values into CBT-I delivery.Collectively, cultural adaptation of CBT-I may increase the relevance of CBT-I for individuals from different cultural backgrounds.
, including factors that may have played 'predisposing', 'precipitating', 'perpetuating', and 'protective' roles in the development and maintenance of insomnia.This formulation is then applied in treatment planning as the clinician tailors CBT-I to each individual.Unlike manualised CBT-I used in research trials, individualising CBT-I means different individuals may receive CBT-I components in different ways, e.g., receiving CBT-I components in different orders, having different treatment lengths, receiving adjunct components for non-sleep-related concerns that may interfere with the implementation of CBT-I (e.g., anxiety, pain).Importantly, a case formulation-based approach to CBT-I requires ongoing assessment beyond the initial evaluation: treatment plans are updated as intervention progresses, and new information is revealed.4 | GAPS AND DIRECTIONS All three types of adaptation, context-, condition-, and individualfocused adaptations, have their place in the implementation of CBT-I in the real world.On one hand, trials testing context-/conditionfocused adaptations provide much needed empirical evidence for how CBT-I could be tailored to an individual with one or more context(s) and condition(s).On the other hand, formulations of individual cases allow continued discovery of areas that need future research and adaptation to improve CBT-I.Abundant trials provided evidence for CBT-I adaptations for specific contexts or comorbid conditions (e.g., CBT-I for chronic pain, depression).Most these trials used traditional parallel group randomised control designs comparing an active and a control condition; further, due to power and resource constraints, they recruited homogenous groups of individuals (e.g., excluding certain conditions), so that treatment recipients were matched to predetermined treatment protocols, rather than adapting the intervention to meet unique characteristics of each individual.A clear gap in the literature is the lack of studies that empirically examined important considerations related to the adaptations and tailoring of CBT-I: (a) what configurations of CBT-I work for whom, and at what stage.The configurations may include aspects such as type(s) of components, dose (e.g., number of sessions, engagement duration), sequence of components; and (b) what is the comparative efficacy and adherence of adapting versus not adapting CBT-I.