Mobility Inventory (MI)

Abstract

The Mobility Inventory (MI), often referred to as the Mobility Inventory for Agoraphobia (MIA), is a widely utilized self-report instrument designed to assess the extent of situational avoidance experienced by individuals suffering from anxiety and agoraphobia. Developed by Chambless and colleagues in 1985, the scale is unique in that it requires respondents to rate their avoidance across various public and travel-related situations under two distinct conditions: when accompanied by a trusted companion and when alone. This dual assessment provides a crucial measure of the severity and pervasiveness of avoidance behaviors, which are central features of agoraphobia and related anxiety disorders.

Keywords

Mobility Inventory, MI, MIA, agoraphobia, situational avoidance, panic disorder, anxiety, behavioral assessment, phobia, self-report scale.

Authors

Chambless, Dianne L., Caputo, G. Craig, Jasin, Susan E., Gracely, Edward J., Williams, Christine.

Purpose

The primary purpose of the Mobility Inventory (MI) is to quantify the degree of behavioral restriction and avoidance related to anxiety and fear in individuals, particularly those diagnosed with or suspected of having agoraphobia. By evaluating avoidance across a standardized set of places and situations, the MI assists clinicians and researchers in establishing baseline severity, monitoring treatment progress, and differentiating between levels of impairment dependent on social support.

A secondary, but critical, function of the inventory is the assessment of panic attacks and the existence of a subjective “Safety Zone.” These additional components allow for a more holistic understanding of the patient’s condition, recognizing that avoidance behavior often stems from the fear of experiencing a panic attack in public settings, a concept sometimes referred to as ‘fear of fear’.

Construct

The Mobility Inventory primarily measures situational avoidance, which is the core behavioral manifestation of agoraphobia. The construct is operationalized through two separate subscales: avoidance when accompanied and avoidance when alone. The difference between these two scores often reflects the degree to which an individual relies on a trusted companion for safety, a phenomenon known as companion dependence.

The scale assumes that avoidance is a continuous variable ranging from “never avoid” to “always avoid.” Additionally, the MI captures related constructs such as the frequency and severity of panic attacks and the delineation of a personal safety zone, which represents an area where the individual feels free from anxiety and is typically able to travel alone.

Validity

The Mobility Inventory has demonstrated robust psychometric properties, particularly concerning validity. Studies, including those by Chambless et al. (2011), have confirmed its convergent validity through strong correlations with other measures of anxiety severity, phobic avoidance, and panic-related distress. This indicates that the MI measures the construct it intends to measure.

Furthermore, the MI exhibits strong discriminant validity, showing less correlation with measures of general mood or depression, suggesting it specifically targets anxiety and agoraphobic avoidance rather than broader psychological distress. Criterion-related validity is supported by the scale’s ability to differentiate between individuals diagnosed with agoraphobia and non-clinical controls, as well as its sensitivity to change following behavioral or cognitive treatments for panic disorder and agoraphobia.

Reliability

The MI possesses excellent internal consistency and test-retest reliability, particularly for the overall avoidance score and the “alone” subscale, which is generally considered the more sensitive measure of impairment. High internal consistency (often measured by Cronbach’s alpha) ensures that all items on the scale consistently measure the underlying construct of avoidance. The stability of scores over time, especially in untreated clinical populations, further supports its reliability as a consistent measure of agoraphobic severity.

Factor Analysis

While the MI is typically scored using the two-factor structure (Avoidance Alone and Avoidance Accompanied), factor analytic studies have consistently supported this inherent structure. The two factors effectively capture the distinct behavioral manifestations of agoraphobia. The “Avoidance Alone” factor usually loads more heavily and is often the primary measure of clinical severity, reflecting the degree of functional impairment when the primary source of external safety (the companion) is absent. Subsequent analyses have confirmed that these two factors reliably account for the majority of the variance in avoidance behavior.

Instrument

Test Type: Self-report Questionnaire

Format: 27-item inventory (situations/places) rated on a 5-point Likert scale (1=never avoid to 5=always avoid), assessed across two conditions (alone/accompanied). Includes additional qualitative items regarding panic attacks and safety zones.

Language Available: Primarily English; translated versions are available and commonly used in international research settings.

Population Group: Clinical populations presenting with Panic Disorder with Agoraphobia (PDA) or Agoraphobia without a history of Panic Disorder.

Age Group: Adults and adolescents (typically 18+ for standard clinical use).

Population Details: Used extensively in clinical trials and research investigating the efficacy of cognitive-behavioral therapy (CBT) and pharmacological interventions for anxiety disorders.

Test Methodology: Respondents indicate their degree of avoidance (1-5) for each situation under two columns: “When Accompanied” and “When Alone.” The scale also prompts the respondent to identify their top five most concerning items and provides space to report the frequency and severity of recent panic attacks.

Keywords

Mobility Inventory, agoraphobia assessment, situational fear, avoidance behavior, self-report, psychometrics, safety zone, companion dependence, Dianne L. Chambless, panic attacks.

Authors

Author ORCID Identifier: NA

Affiliation Email addresses: NA

Correspondence Address: NA

Permissions & Fee and Test Year

The Mobility Inventory (MI) was first published in 1985. It is widely used in academic research and clinical settings. Researchers and clinicians should typically contact the primary author, Dianne L. Chambless, or consult the original publication in Behaviour Research and Therapy regarding specific permission requirements for commercial or large-scale use. The original PDF can be downloaded here: https://outcometracker.org/library/MIA.pdf

Reference’s

• Chambless, Dianne L., Caputo, G. Craig, Jasin, Susan E., Gracely, Edward J., Williams, Christine. (1985). The Mobility Inventory for Agoraphobia. Behaviour Research and Therapy. 23(1); 35–44.

• Chambless, D. L., & Gracely, E. J. (1989). Fear of fear and the anxiety disorders. Cognitive Therapy and Research, 13, 9-20.

• Chambless, Dianne L., Sharpless, Brian A., Rodriguez, Dianeth., McCarthy, Kevin S., Milrod, Barbara L., Khalsa, Shabad-Ratan., and Barber, Jacques P. (2011). Psychometric Properties of the Mobility Inventory for Agoraphobia: Convergent, Discriminant, and Criterion-Related Validity. Behav Ther, 42(4); 689-599. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3519241/

Items of the Mobility Inventory (MI)

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

Please indicate the degree to which you avoid the following places or situations because of discomfort or anxiety. Rate your amount of avoidance when you are with a trusted companion and when you are alone. Do this by using the following scale:

1- never avoid, 2- rarely avoid, 3- avoid about half of the time, 4- avoid most of the time, 5- always avoid

Circle the number for each situation or place under both conditions: when accompanied and when alone.

Leave blank situations that do not apply to you.

2. After completing the first step, circle the 5 items with which you are most concerned. Of the items listed, these are the five situations or places where avoidance/anxiety most affects your life in a negative way.

PANIC ATTACKS

3. We define a panic attack as:

1. A high level of anxiety accompanied by………
2. strong body reactions (heart palpitations, sweating, muscle tremors, dizziness, nausea) with…….
3. the temporary loss of the ability to plan, think, or reason and……….
4. the intense desire to escape or flee the situation (Note: this is different from high anxiety or fear alone).

Please indicate the number of panic attacks you have had in the past 7 days:___________

How severe or intense have the panic attacks been? (Place an X on the line below):

1- Very mild, 2- mild, 3- moderately, 4- very, 5- extremely

Safety Zone

4. Many people are able to travel alone freely in the area (usually around their home) called their safety zone.

Do you have such a zone? If yes, please describe:

a. Its location:

b. Its size (e.g. radius from home):