Unified Parkinson’s Disease Rating Scale Part II was used in 34.1% (n = 44) of the included studies.

Construct assessed: Disease severity.

Test description: The UPDRS is a disease-specific rating scale containing 55 items grouped into four subscales: Part I – mentation, behavior, and mood; Part II – activities of daily living; Part III – motor exam; and Part IV – complications of therapy (in the past week). A lower score represents less disability in performing ADL in PD. According to its description, the average time required to administer the full scale is between 10 and 20 min (Movement Disorder Society Task Force on Rating Scales for Parkinson’s Disease, 2003).

Clinimetric properties: Specifically designed for the PD population. Test-retest reliability is excellent (ICC = 0.92) for the entire scale and substantial (ICC = 0.85) for the ADL section. It has adequate internal consistency (Cronbach’s alpha = 0.96) and inter-rater reliability (k ≥ 0.4), criterion, and convergent validity. The clinimetric properties for Part II as an independent scale were already studied and showed that floor and ceiling effects, convergent validity, reliability, and standard error of measurement, found to be adequate (Martinez-Martin et al., 2006), suggesting that the UPDRS Part II generally would be considered a psychometrically sound tool for measuring ADL outcomes in people with PD (Ramaker et al., 2002; Siderowf et al., 2002; Hariz et al., 2003; Martínez-Martín et al., 2003; Hagell, 2019).

Feasibility: The UPDRS has several advantages, including the ability to provide a comprehensive assessment of the main features of PD while requiring little material (just a pencil or a pen and a chair). Its main drawbacks are its reliance on the expertise of the evaluator and the amount of time it takes. Although it is estimated to take 10–20 min, due to the numerous topics that must be discussed with the patient, it may take longer, limiting its use in clinical practice. The Movement Disorder Society (MDS) sponsored a critique of the UPDRS in 2001, which praised the scale’s strengths while pointing out several ambiguities, flaws, and areas that needed to be included to reflect current scientific developments. In 2008, the MDS developed a new version of the scale, which addressed some of the original scale’s flaws and included several clinically relevant PD-related issues that were underrepresented in the original version. Although the new version of the scale was recommended, the transition was not immediate as the old version had been used in several studies after 2008 (Hoehn and Yahr, 1967; Fahn et al., 1987; Movement Disorder Society Task Force on Rating Scales for Parkinson’s Disease, 2003; Goetz et al., 2007; Martinez-Martin et al., 2013; Bloem et al., 2016).

Schwab and England Daily Living Activities Scale was used in 23.3% (n = 30) of the included studies.

Construct assessed: Ability to perform ADL.

Test description: The S&E is a single-item self-rated scale created specifically for people with PD. Patients are asked to rate their ability to perform ADL from 0% (bedridden) to 100% (completely independent). This instrument takes about 5 min to administer (Schwab and England, 1968; Siderowf, 2010).

Clinimetric properties: The test-retest and inter-rater reliabilities of the instrument are both adequate (ICC = 0.7 and 0.6, respectively). A 10-point change was reported as the minimum clinically significant difference (Schwab and England, 1968: Ramaker et al., 2002; Siderowf, 2010; Dal Bello-Haas et al., 2011).

Feasibility: Based on patients’ own perceptions, the S&E provides a global impression of patients’ level of independence in performing ADL. Because it is a single-item scale, it is very quick and easy to use, and no prior training is required. It is impossible to differentiate between the most difficult activities and precise limitations (Ramaker et al., 2002; Siderowf, 2010).

Movement Disorder Society-Unified Parkinson’s Disease Rating Scale Part II was used in 7.0% (n = 9) of the included studies.

Construct assessed: Disease severity.

Test description: The MDS-UPDRS preserves the UPDRS’ four-part structure, with 65 items and five possible answers: 0 = normal, 1 = slight, 2 = mild, 3 = moderate, and 4 = severe. Parts I (items 1.7–1.13) and II have been designed to fit into a patient/caregiver questionnaire format, allowing them to be completed without the assistance of the investigator. All questions in Part I that deal with complex behaviors (items 1.1–1.6) and all questions in Part IV that deal with motor fluctuations and dyskinesias require the investigator to conduct the interview. Part III keeps the objective assessments of parkinsonism but has now more detailed instructions (Martinez-Martin et al., 2013).

Clinimetric properties: The MDS-UPDRS, which was created specifically for people with PD, has high internal consistency (Cronbach’s alpha = 0.79–0.93 across parts) and is highly correlated with the original UPDRS (q = 0.96). It also has an excellent construct validity (r = 0.92). The instrument has strong concurrent validity based on high correlations with the UPDRS (total score r = 0.96), as well as between the individual parts of the two scales. According to Rodriguez-Blazquez et al. (2013), the part II of MDS-UPDRS correlates with other disability measures (Rapid Assessment of Disability Scale and Clinical Impression of Severity Index for PD, r = 0.70–0.80) and quality of life scales (Parkinson’s Disease Questionnaire-8 and EQ-5D, r = −0.46 to 0.74), which proves useful for assessing disability in PD (Forjaz and Martinez-Martin, 2006; Martinez-Martin et al., 2013; Rodriguez-Blazquez et al., 2013).

Feasibility: The MDS-UPDRS has the advantage of being a more complete instrument, with better instructions for quoting the different items. However, as the number of questions has increased, it will take longer to complete the full scale. The assessment of ADL is performed through Part II, which, in addition to being validated to be used independently, is built in a self-completed questionnaire format. It can be completed by the patient and/or the caregiver.

The Barthel Index was used in 7.0% (n = 9) of the included studies.

Construct assessed: Performance in ADL.

Test description: The Barthel Index was designed to monitor progression in individuals with chronic diseases who are undergoing rehabilitation. It is a 10-item ordinary scale that assesses a person’s ability to conduct ADLs independently, such as feeding, bathing, grooming, dressing, bladder control, bowel control, toilet use, transfers (bed to chair and back), mobility (on a level surface), and stairs (ascending and descending). It can take 5–20 min depending on how the assessment is performed (self-report vs. direct observation). Higher scores imply greater functional independence, with a severity cut-off of 0–20 indicating “complete” dependency, 21–60 indicating “severe” dependency, 61–90 indicating “moderate” dependency, and 91–99 indicating “slight” dependency (Morley et al., 2012; Taghizadeh et al., 2020).

Clinimetric properties: Although not specifically designed, it has been validated for the PD population. In both medication phases it has an excellent test/retest reliability (ICC = 0.84 in ON, ICC = 0.77 in OFF), inter-rater/intra-rater reliability (ICC = 0.91 in ON, ICC = 0.90 in OFF) and internal consistency (Cronbach’s alpha = 0.85 in ON, Cronbach’s alpha = 0.88 in OFF). It also has moderate to high convergent validity in ON and OFF phases (ρ = 0.48–0.82) (Collin et al., 1988; Wade and Collin, 1988; Morley et al., 2012; Taghizadeh et al., 2020).

Feasibility: The Barthel Index is a straightforward tool that takes only a few minutes to complete and provides a global but comprehensive view of the patient’s ADL performance. It can be used in both the early and advanced stages of the disease because it can be used as a self-completion questionnaire or for direct observation. The rating system uses the numbers 0–unable, 1–requires assistance, and 2–independent, which does not allow for a detailed description of the difficulties in each task (Wade and Collin, 1988).

The Lawton-Brody scale was used in 4.7% (n = 6) of the included studies.

Construct assessed: Independent living skills.

Test description: Lawton and Brody developed this scale in 1969 to measure disability levels and assess parameters in community-dwelling older adults. This scale includes eight items, including telephone use, shopping, food preparation, housekeeping, laundry, public transportation use, self-medication management, and financial management. Patients are graded on a scale of 0 (cannot or partially perform) to 1 (can perform) based on their highest level of functioning. The total score ranges from 0 (low functioning, dependent) to 8 (high functioning, independent). The assessment takes about 10–15 min to complete (Graf, 2008).

Clinimetric properties: The clinimetric properties of the scale have not been assessed in the PD population. In older adults the instrument has adequate inter-rater reliability (ICC = 0.85). Its validity was tested by determining the correlation with four scales that measure domains of functional status: Physical Classification (6-point rating of physical health), Mental Status Questionnaire (10-point test of orientation and memory), Behavior and Adjustment rating scales (4–6-point measure of intellectual, person, behavioral, and social adjustment), and the Physical Self-Maintenance Scale (6-item ADLs) and all the correlations were significant at the.01 or.05 levels. The scale has also been validated for people with dementia, showing a moderate internal consistency and excellent test-retest reliability (Edwards, 1990; Graf, 2008; Hassani Mehraban et al., 2014; The Memora Group et al., 2021).

Feasibility: Unlike the most, the Lawton-Brody scale is focused on instrumental ADL. Despite being an easy and quick to use instrument, it may not be sensitive to small changes. Since some items, such as meal preparation and laundry, are the tasks and responsibilities not performed by institutionalized patients (and men in some cultures) its use is not advised, due to the fact that the lack of responsiveness to some questions is due to cultural differences, not because of the inability to perform those tasks.

The Functional Independence Measure (FIM) was used in 3.9% (n = 5) of the included studies.

Construct assessed: Disability.

Test description: The FIM is a seven-level ordinal scale with 18 items that assess a patient’s level of disability as well as changes in their status in response to a therapeutic intervention. The domains assessed are self-care independence, such as sphincter control, transfers, locomotion, communication, and social cognition, which are usually assessed through observation. The level of assistance required is used to grade functional status, which ranges from total independence to total assistance. The total score ranges from 18 to 126, with each item having a value ranging from 1 (complete dependence) to 7 (complete independence) (Dodds et al., 1993).

Clinimetric properties: The clinimetric properties of the scale have not been assessed in the PD population. Studies in older adults have shown an excellent test-retest reliability (ICC = 0.98) and studies in neurological disorders (not specified which) showed excellent internal consistency (Cronbach’s alpha = 0.95) (Keith et al., 1987; Dodds et al., 1993; Linacre et al., 1994; Hobart et al., 2001; Hsueh, 2002; Coster et al., 2006; Ng et al., 2007; Ellis et al., 2008).

Feasibility: The FIM provides realistic and detailed information about a patient’s level of self-care disability. It has the drawbacks of requiring training, being time-consuming (it takes 30–45 min to administer) and requiring environmental conditions that allow self-care tasks to be performed.

The Alzheimer’s Disease Cooperative Study – Activities of Daily Living Inventory (ADCS-ADL) was used in 3.9% (n = 5) of the included studies.

Construct assessed: Ability to perform ADLs.

Test description: The ADCS-ADL is a questionnaire administered by the rater, in in-person assessments, or by telephone. It was developed to identify which ADLs are useful for the assessment of patients in clinical trials in the Alzheimer’s disease (AD) field. It includes 23 items, 6 basic ADL items, and 17 instrumental ADL items. The total score ranges from 0 to 78, with a lower score indicating greater severity (Galasko et al., 1997).

Clinimetric properties: The ADCS-ADL was constructed specifically for use with AD patients. The clinimetric properties of the scale have not been assessed in the PD population (Galasko et al., 1997; Kahle-Wrobleski et al., 2014).

Feasibility: It is a time-consuming instrument, based on the patient/caregivers’ perspective on the ability to perform ADL. It was developed for AD and research purposes.