Behavioral rigidity, the tendency to maintain inflexible patterns of thinking and acting despite changing circumstances, is a common feature in substance use disorders, depression, and anxiety. This observational study aims to measure behavioral rigidity as a dynamic, transdiagnostic process in patients undergoing residential treatment for substance use. Using a longitudinal intensive repeated-measures design, participants complete weekly assessments of cognitive reactivity (Automatic Thoughts Questionnaire-8 item version, ATQ-8), behavioral activation (Behavioral Activation for Depression Scale, BADS), and experiential avoidance. A Behavioral Rigidity Index (BRI) is derived from these measures. Additionally, natural language processing (NLP) is applied to therapy session transcripts to quantify linguistic absolutism (e.g., use of words like "always," "never") and affective polarity. Bayesian multilevel models examine whether rigidity predicts current and next-week clinical status. The study also explores whether linguistic markers add unique predictive value beyond self-reports. Results may inform personalized monitoring and interventions targeting psychological inflexibility in addiction treatment.

This is an observational, longitudinal intensive study with repeated measures (weekly assessments) conducted in a residential therapeutic community in Mexico. Participants are adults (N=34, age 18-60) with substance use disorder and co-occurring emotional dysregulation or behavioral maladaptation, receiving standard psychosocial treatment (not assigned by the research protocol). Inclusion requires a minimum stay of four weeks, at least three complete measurement time points, and ability to complete self-reports. Exclusion criteria: severe neurocognitive impairment, acute psychotic symptoms, or incomplete longitudinal records.

Measures are collected at the beginning of each weekly therapy session:

Automatic Thoughts Questionnaire-8 (ATQ-8): frequency of negative automatic thoughts (higher scores indicate more frequent negative automatic thoughts).

Behavioral Activation for Depression Scale (BADS): subscales of Activation (goal-directed activity) and Avoidance/Rumination (experiential avoidance).

From these, a Behavioral Rigidity Index (BRI) is computed in two versions:

BRI-Simple (BRI-S): sum of standardized intraindividual scores of ATQ-8 + BADS-Avoidance - BADS-Activation.

BRI-Pondered (BRI-P): weighted combination derived from principal component analysis of the three standardized scores. The first principal component explained the majority of the common variance, supporting unidimensionality of the construct.

Additionally, natural language processing (NLP) pipelines are applied to transcribed therapy sessions and self-registries. Text is tokenized, lemmatized, and normalized by document length. Four linguistic domains are extracted:

Affective polarity: density of negative/positive terms.

Linguistic absolutism: frequency of extreme quantifiers (e.g., "always", "never", "everything", "nothing").

Grammatical agency: proportion of active vs. passive voice sentences.

Lexical complexity: type-token ratio and entropy.

A Linguistic Rigidity Index (LRI) is created by standardizing and averaging absolutism scores and inverted negative polarity (higher LRI = greater linguistic rigidity).

Statistical analysis uses Bayesian multilevel models with random intercepts by participant. The outcome variable is intraindividual standardized ATQ-8 (ATQ8_total_z). Predictors include time in treatment, BRI (contemporary and lagged by one week), and LRI. Model comparison will be performed using information criteria appropriate for multilevel models. Secondary analyses explore dynamic systems metrics derived from the state space defined by ATQ-8 and BRI-P, such as deviation from typical states and return speed after disturbances.

All procedures comply with the Declaration of Helsinki. The protocol was approved by the institutional ethics committee (Comité de Ética en Investigación de la Comunidad Terapéutica Under The Tree). Participants gave informed consent for anonymized use of their clinical data for research purposes.

Inclusion Criteria:

• Minimum stay of four weeks in the residential treatment program
• At least three complete longitudinal measurement time points
• Ability to read, understand, and respond to self-report instruments in Spanish
• Capacity to participate in structured clinical sessions
• Diagnosis of substance use disorder (clinical assessment)

Exclusion Criteria:

• Severe neurocognitive impairment
• Acute psychotic symptoms
• Incomplete longitudinal records (less than three time points)
• Inability to complete self-report measures due to cognitive or language barriers

Adult patients (age 18-60) with substance use disorder and co-occurring emotional dysregulation or behavioral maladaptation, admitted to a residential therapeutic community in Mexico. The sample includes both sexes, with an expected predominance of males (approximately 85%). Participants are receiving standard psychosocial treatment, including individual and group therapy, 12-step facilitation, and occupational activities. No healthy volunteers are included.