The present project aims at testing the feasibility of an app-based system called "EmoGuía" for routine outcome monitoring of adult patients with emotional disorders while they are administered a self-applied online transdiagnostic psychological intervention.

Anxiety and depressive disorders, commonly known as emotional disorders (EDs), are the most frequent mental health problems why patients seek for medical care globally. According to recent epidemiologic studies, lifetime prevalence rates reveal that anxiety and depression disorders affect approximately an estimated 31.9% and 33.7% of people worldwide, respectively. In Spain, a nationwide study showed a prevalence of anxiety and depression disorders of 5.2% and 4.1%, approximately. Consequently, EDs lead to considerable direct and indirect economic losses for countries, as well as a great negative impact on the quality of life and overall functioning of individuals. Adding up to the previous, the current covid-19 pandemic not only has boosted the incidence of mental disorders in healthy people, but also has exacerbated emotional problems in vulnerable populations.

Encouragingly, the effectiveness of psychotherapy for the treatment of EDs, especially cognitive behavioural therapy (CBT), has been supported by a vast amount of scientific evidence. In particular, Internet-delivered CBT (iCBT), where patients sign in to a safe website to access online psychotherapeutic materials within several modules, has emerged in recent years as an effective alternative to face-to-face psychotherapy in an attempt to reduce costs, save therapists' and clients' time, bring psychological treatments closer to the population, and disseminate interventions easily. The growth of digital care has become even more obvious during the covid-19 pandemic and the associated quarantine, where great efforts have been made to adapt evidence-based treatments to a new digital format. Therefore, the current situation has become an opportunity to develop and implement promising digital interventions, which are now more sensible than ever.

To make evidence-based treatments even more accessible, extensions and innovations of CBT have been developed in recent years. The latest research supports a transdiagnostic perspective for the treatment of EDs, where cognitive-behavioural techniques are included to target different EDs altogether. Indeed, the transdiagnostic approach appears to be an effective alternative to single disorder interventions in order to address the high comorbidity rates between anxiety and depressive disorders, as well as the shared mechanisms and the overlapping symptomatology across different disorders which play an essential role in the onset and maintenance of them. In particular, the Unified Protocol (UP), a transdiagnostic extension of CBT which works on regulate emotions in a more adaptive way through different core treatment modules, has been developed for the treatment of EDs. Specifically, the UP shows promising effects not only when delivered onsite, but also online, which makes it an excellent psychological approach to reach a large number of individuals with a single treatment protocol.

In this line, some interesting proposals emphasize the need for a paradigm shift from randomized controlled trials that work on average towards personalized treatments that allow to focus more on the individual (to avoid what group average can mask). In particular, measurement-based care, which consists of routine patient monitoring, periodic feedback to the therapist (or both therapist and patient), and adaptation of the intervention according to such feedback appears to be a feasible option in order to adapt treatments to patients' needs. Fortunately, with the rapid growth of new technologies in our society such as mobile applications (apps), measurement-based care can be implemented more effectively as the apps can be used as support tools for the assessment of several psychological outcome variables. This procedure is commonly known as Ecological Momentary Assessment (EMA) and can help overcome some of the obstacles that traditional, retrospective face-to-face assessments hold. EMA has the potential to assess patients repeatedly and frequently over time, allows to observe fluctuations in patient outcomes, and early interventions can be administered in response to pre-set clinical alarms.

To our knowledge, studies that use technology to improve the management of emotional problems have generally opted for using apps that report on the evolution of treatment to obtain more reliable measures of the evolution of patients or, more frequently, have used different technologies such as web pages or apps to facilitate self-applied treatments based on pre-established modules. The present study goes one step further and explores not only the usefulness of the EMA by means of an app for the improvement of the assessment process of patients with emotional problems/EDs, but also the feasibility of using it to make adjustments in real time or very short-term (e.g., in weekly visits) during the psychotherapeutic process, resembling an ecological momentary intervention (EMI). Several studies have supported the use of EMA to deliver the most personalized feedback or psychological support in real life for a given patient in order to enhance psychotherapy effectiveness and facilitate tailored treatments.

Objectives The current study aims to explore the feasibility of an app-based system called "EmoGuía" a recently developed app that will provide personalized measurement-based care (MBC) based on EMIs according to the patients' daily evolution observed with daily evolution/assessment observed in the app (Castilla et al., 2022a). The EMI app will complement a self-applied online transdiagnostic treatment for people with EDs, which has shown to be effective in past research (Díaz-García et al., 2021).

The objectives of this feasibility study are: (1) to test whether the EMI app is appraised as simple to use, useful and acceptable by both patients and psychologists (app usability, satisfaction, and acceptability) and, (2) to test the number of completed assessments and transdiagnostic modules from those suggested (adherence to the app and treatment compliance). As a secondary goal, we will investigate the potential effectiveness of the EMI app by exploring whether changes in outcome variables and mechanisms of change (anxiety, depression, and emotion regulation) occur after the app use at an individual level.

We anticipate that the implementation of the app "EmoGuía" will be feasible in terms of usability, satisfaction, acceptability, compliance, retention rates, and adherence. Thus, we expect that patients and psychologists will perceive the app to be useful, will experience low burden associated with its use, and will be satisfied with the procedure. We also expect to improve the mood status and emotion regulation outcomes in a large number of participants.

The design of a future clinical trial will be optimized with the aforementioned objectives. The current article describes the study protocol of this trial.

Inclusion Criteria:

1. age ≥18 years
2. showing problematic levels (one standard deviation above or below the mean) in at least one of the 9 transdiagnostic dimensions of the Multidimensional Emotional Disorders Inventory (MEDI; Osma et al., 2021; Rosellini & Brown, 2019) or having moderate-to-severe anxiety (scores ≥8) or depressive symptoms (scores ≥5), as reported in the Overall Anxiety Severity and Impairment Scale (OASIS) and the Overall Depression Severity and Impairment Scale (ODSIS) (Mira et al., 2019)
3. having the ability to read and understand Spanish
4. having a computer and a mobile phone Internet access
5. signing the online informed consent.

Exclusion criteria:

1. age <18
2. severe mental health problems
3. high suicide risk
4. receiving psychological treatment for the same ED emotional problem targeted by our study at the same time the current study is being conducted
5. <8 in OASIS and <5 in ODSIS, or non-problematic scores in the MEDI
6. have changes and/or increases in pharmacological treatment during the study (stable medication will be accepted).

Individual Participant Data (IPD) will not be shared with other researchers.

Patients will be informed of the condition they have been assigned to.