The Fatigue Assessment Scale (FAS) is a 10-item self-report measure of general fatigue, assessing both physical and mental symptoms in adults.
Fatigue is a common and disabling experience, affecting daily functioning and quality of life. It can be defined as a subjective experience of tiredness, lack of energy, and reduced motivation that is perceived to interfere with usual functioning. Fatigue manifests across physical, cognitive, and emotional domains and often persists despite adequate rest.
The FAS is a 10-item self-report measure of general fatigue (Michielsen et al., 2003). It assesses fatigue as a single overall construct while ensuring coverage of both physical symptoms (e.g., physical exhaustion, lack of energy, tiring quickly) and mental symptoms (e.g., lack of motivation, problems thinking clearly, difficulty initiating tasks). The FAS was originally developed in Dutch by selecting and refining items from four established fatigue questionnaires (Michielsen et al., 2004). It has since been translated into numerous other languages and used across a range of populations and conditions (Hendriks et al., 2018).
The FAS has been widely used in clinical practice and research. It can be used to quantify the presence and severity of fatigue, monitor changes in fatigue over time, and evaluate treatment effectiveness. It is appropriate for use across a range of clinical contexts, including both mental and physical health care.
The FAS yields a total score between 10 and 50, with higher scores indicating more severe fatigue. Each item is rated on a 5-point Likert-type scale from 1 to 5 reflecting the frequency with which the respondent usually experiences a specific physical or mental symptom of fatigue. Items 4 and 10 are reverse-scored.
Scores are also provided for the scale’s two subscales (Drent et al., 2012):
The respondent’s total FAS score is expressed as a percentile based on normative data for working adults in the general Dutch population (De Vries et al., 2003; Michielsen et al., 2003), contextualising their score relative to the typical scores of working adults. For example, the 50th percentile represents the typical level of general fatigue among working adults in the general population, while scores on the 90th percentile fall within the top 10% and are considered “Moderate”, and scores on the 99th percentile fall within the top 1% and are considered “Severe”.
Total FAS scores of 22 or above are commonly cited as indicating the presence of significant fatigue. This threshold corresponds approximately to the 65th percentile of the normative sample of working adults and was originally based on the observation that scores at this level differentiated the majority of patients with sarcoidosis from the general population (De Vries et al., 2004). It is important to note that this cut-off score is not a formally validated threshold for identifying people with clinically significant fatigue.
Hendriks and colleagues (2018) reported that total FAS scores of less than 22 indicate no substantial fatigue, scores between 22 and 34 indicate mild-to-moderate fatigue, and scores of 35 or above indicate severe fatigue. To further aid in clinical interpretation, NovoPsych distinguishes between mild fatigue (scores between 22 and 27) and moderate fatigue (scores between 28 and 34).
Although these severity classifications have not been validated, the category boundaries correspond approximately to the 65th, 90th, and 99th percentiles of the normative sample of working adults, representing progressively higher levels of fatigue relative to the general working population. These classifications provide useful clinical interpretation guidelines for contextualising a respondent’s score.
On first administration, a graph is presented showing the respondent’s total FAS score, consisting of the subscale scores for Physical Fatigue and Mental Fatigue. If administered more than once, longitudinal graphs are presented for the total score and subscale scores, indicating if there have been any changes in these scores over time.
A clinically meaningful change in overall fatigue is defined as a change of 4 or more points in the total FAS score, based on the Minimal Clinically Important Difference (MCID) established by de Kleijn and colleagues (2011) in patients with sarcoidosis. Specifically, a 4 or more point increase indicates a clinically meaningful worsening of fatigue, a 4 or more point decrease indicates a clinically meaningful improvement in fatigue, and less than a 4-point change indicates no clinically meaningful change.
The psychometric properties reported below are based on the original Dutch-language validation studies conducted with Dutch general population and clinical samples.
The FAS demonstrates strong internal consistency, with Cronbach’s alpha coefficients of .87 to .90 across multiple samples (Michielsen et al., 2003; Michielsen et al., 2004; De Vries et al., 2003; De Vries et al., 2004). Test-retest reliability over a one-week interval is excellent (r = .89; De Vries et al., 2004).
Factor analytic studies consistently support the FAS as a unidimensional measure of general fatigue (Michielsen et al., 2003; Michielsen et al., 2004; De Vries et al., 2003; De Vries et al., 2004). While subscale scores for physical and mental fatigue can be calculated based on item content, these reflect different manifestations of a single underlying construct rather than distinct dimensions.
FAS scores correlate strongly with other established fatigue measures, including the Checklist Individual Strength (CIS) fatigue subscale and the WHOQOL-100 Energy and Fatigue subscale (De Vries et al., 2003; De Vries et al., 2004). In a comparative analysis of six fatigue questionnaires in a general working adult sample, the FAS had the highest factor loading on a single-factor solution, supporting its construct validity as a measure of general fatigue (De Vries et al., 2003).
The FAS demonstrates appropriate discriminant validity from depression. While fatigue and depression are correlated constructs, factor analyses confirm they represent distinct dimensions, indicating that the FAS measures fatigue specifically rather than general psychological distress (Michielsen et al., 2003).
The FAS differentiates between groups expected to differ in fatigue levels. In a Dutch sample, patients with sarcoidosis (an inflammatory disease often associated with fatigue) scored significantly higher than the general working adult population, with the majority of sarcoidosis patients scoring ≥22 compared to the majority of general working adults scoring <22 (De Vries et al., 2004).
Normative data for the FAS are based on a general population sample of 351 Dutch adults aged 21 to 65 years who were working 20 or more hours per week. In this sample, the mean total FAS score was 19.26 (SD = 6.52), with scores approximately normally distributed (De Vries et al., 2003; Michielsen et al., 2003). These data are used to convert the respondent’s total FAS score to a percentile, providing useful information about the severity of their general fatigue relative to working adults in the general population.
Fatigue, as measured by the FAS, is distinct from the everyday tiredness that most people experience after exertion or inadequate sleep. Whilst normal tiredness typically resolves with rest and is proportionate to activity levels, clinically significant fatigue is persistent, often disproportionate to recent activity, and may not improve substantially with rest or sleep. It can affect a person’s capacity to engage in work, social activities, and self-care, and frequently influences overall quality of life.
Fatigue becomes a clinical concern when it is persistent, causes distress, and interferes with daily functioning. Because it is not always apparent to others or detectable with objective clinical markers, it is important to ask a person about their subjective experience of fatigue.
The FAS captures this subjective experience by asking about physical exhaustion, mental exhaustion, energy levels, motivation, and concentration. Higher scores indicate that a person is experiencing more frequent and intense fatigue that is likely affecting their daily functioning, rather than transient tiredness that most people would consider unremarkable.
Fatigue frequently accompanies a wide range of physical and mental health conditions. It is commonly reported in chronic diseases such as sarcoidosis, cancer, heart failure, diabetes, rheumatoid arthritis, and stroke, as well as in mental health conditions including depression, anxiety, chronic stress, and burnout. However, research has consistently demonstrated that fatigue is a distinct construct that can exist independently of, or alongside, these conditions.
Studies comparing the FAS with depression measures have found that fatigue and depression are distinguishable experiences, even when they co-occur. This has important clinical implications: a person may present with significant fatigue without meeting criteria for a depressive or other disorder, or their fatigue may persist even after other symptoms have responded to treatment. Because fatigue independently contributes to reduced quality of life, it may require specific attention rather than being treated as secondary to other conditions.
The FAS can be a useful tool for assessing fatigue that may accompany mood disorders, anxiety, chronic stress, burnout, or physical health conditions. It can also help identify fatigue related to medications or lifestyle factors. Because the FAS measures fatigue as distinct from other symptoms, it provides information that complements other assessments and can inform treatment planning by highlighting whether fatigue warrants specific attention alongside other presenting concerns.
Fatigue is a common complaint and is frequently reported by individuals with chronic physical and mental health conditions. Despite its prevalence, fatigue is often underassessed. It may be overlooked when the clinical focus is on other presenting concerns, or assumed to be a secondary symptom that will resolve once other conditions improve, potentially leaving it untreated and undermining the effectiveness of other treatment interventions.
For mental health professionals, assessing fatigue can help identify treatment targets and monitor treatment progress. Because fatigue can accompany depression, anxiety, and other presentations, assessment of fatigue ensures that it receives appropriate clinical attention.
The commonly cited FAS cut-off scores and severity classifications were derived primarily from research with sarcoidosis patient populations. Scores below 22 are typically interpreted as indicating no substantial fatigue, scores between 22 and 34 as mild-to-moderate fatigue, and scores of 35 or above as severe fatigue. Whilst these thresholds have been widely cited, their validity has not been systematically established across the diverse range of conditions in which the FAS is now used.
For example, a study examining poststroke fatigue suggested that a cut-off of 24, rather than 22, may be more appropriate for defining clinically significant fatigue in that population. This highlights that optimal thresholds may vary depending on the clinical context and the characteristics of the population being assessed.
To provide additional granularity for clinical interpretation, NovoPsych separates the mild-to-moderate range (scores between 22 and 34) into mild fatigue (scores between 22 and 27) and moderate fatigue (scores between 28 and 34). These categories correspond to logical and progressively higher percentile ranges in a normative sample of working adults, though, like the original classifications, they should be used as clinical interpretation guidelines rather than formally validated severity classification thresholds.
Rather than applying cut-off scores and severity classifications rigidly, clinicians may find it more informative to use the FAS as a dimensional measure, interpreting scores along a continuum. The FAS is particularly valuable for tracking changes in fatigue over time and for facilitating discussion about how fatigue is affecting a person’s daily life, regardless of whether their score falls above or below a particular threshold. When cut-off scores are used, clinicians should be mindful of the limitations of these thresholds and avoid over-interpreting categorical classifications.
The FAS is well-suited for routine outcome monitoring and can be administered at baseline and at regular intervals during treatment to track changes in fatigue severity. The Minimal Clinically Important Difference (MCID) for the FAS has been established at four points, meaning that a reduction of four or more points on the total score indicates a clinically meaningful improvement in fatigue.
The FAS asks respondents to rate how they “usually feel,” which provides flexibility in terms of the recall period but can make comparisons across time points less precise. Some clinicians specify a defined recall period (e.g., the past week or fortnight) to improve comparability.
Because fatigue often has multiple causes, including psychological factors such as depression and anxiety, physical symptoms, and lifestyle factors, the FAS can help clinicians identify whether interventions are effectively addressing the fatigue component specifically, even when other symptoms may or may not be responding to treatment. This makes it a valuable addition to broader outcome monitoring protocols that include measures of mood, functioning, and quality of life.
Michielsen, H. J., De Vries, J., & Van Heck, G. L. (2003). Psychometric qualities of a brief self-rated fatigue measure: The Fatigue Assessment Scale. Journal of Psychosomatic Research, 54(4), 345–352. https://doi.org/10.1016/s0022-3999(02)00392-6
Cumming, T. B., & Mead, G. (2017). Classifying post-stroke fatigue: Optimal cut-off on the Fatigue Assessment Scale. Journal of Psychosomatic Research, 103, 147–149. https://doi.org/10.1016/j.jpsychores.2017.10.016
de Kleijn, W. P. E., De Vries, J., Wijnen, P. A. H. M., & Drent, M. (2011). Minimal (clinically) important differences for the Fatigue Assessment Scale in sarcoidosis. Respiratory Medicine, 105(9), 1388–1395. https://doi.org/10.1016/j.rmed.2011.05.004
De Vries, J., Michielsen, H. J., & Van Heck, G. L. (2003). Assessment of fatigue among working people: A comparison of six questionnaires. Occupational and Environmental Medicine, 60(Suppl 1), i10–i15. https://doi.org/10.1136/oem.60.suppl_1.i10
De Vries, J., Michielsen, H., Van Heck, G. L., & Drent, M. (2004). Measuring fatigue in sarcoidosis: The Fatigue Assessment Scale (FAS). British Journal of Health Psychology, 9(Pt 3), 279–291. https://doi.org/10.1348/1359107041557048
Drent, M., Lower, E. E., & De Vries, J. (2012). Sarcoidosis-associated fatigue. European Respiratory Journal, 40(1), 255–263. https://doi.org/10.1183/09031936.00002512
Hendriks, C., Drent, M., Elfferich, M., & De Vries, J. (2018). The Fatigue Assessment Scale: Quality and availability in sarcoidosis and other diseases. Current Opinion in Pulmonary Medicine, 24(5), 495–503. https://doi.org/10.1097/MCP.0000000000000496
Michielsen, H. J., De Vries, J., & Van Heck, G. L. (2003). Psychometric qualities of a brief self-rated fatigue measure: The Fatigue Assessment Scale. Journal of Psychosomatic Research, 54(4), 345–352. https://doi.org/10.1016/s0022-3999(02)00392-6
Michielsen, H. J., De Vries, J., Van Heck, G. L., Van de Vijver, F. J. R., & Sijtsma, K. (2004). Examination of the dimensionality of fatigue: The construction of the Fatigue Assessment Scale (FAS). European Journal of Psychological Assessment, 20(1), 39–48. https://doi.org/10.1027/1015-5759.20.1.39
