Interventions for fatigue in Parkinson's disease

  • Protocol
  • Intervention

Authors


Abstract

This is the protocol for a review and there is no abstract. The objectives are as follows:

To evaluate the effects of pharmacological and non-pharmacological interventions, compared with an inactive control intervention, on subjective fatigue in patients with PD.

Background

Fatigue is common in patients with idiopathic Parkinson's disease (PD) and has a negative impact on health-related quality of life (HRQOL) (Havlikova 2008; Herlofson 2003; Martínez-Martín 2006). Prevalence rates reported in the literature range from 32% to 50% (Alves 2004; Herlofson 2002). Fatigue usually refers to difficulty initiating or sustaining voluntary activity (Chaudhuri 2004). Its many facets are believed to result from a complex interplay between the underlying disease process, peripheral control systems (i.e. muscle fatigability), central control systems (i.e. subjective sense of fatigue) and environmental factors (Chaudhuri 2004). Subjective fatigue is often subdivided into physical and mental fatigue. Physical fatigue involves a sense of physical exhaustion and lack of energy to perform physical tasks despite the ability and motivation to perform the task (Friedman 2010). Mental fatigue refers to the cognitive effects experienced during and after prolonged periods of cognitive activities that require sustained concentration and mental endurance (Friedman 2010).

Although several potential pathophysiological mechanisms for fatigue (e.g. involvement of cytokines, abnormalities of the hypothalamic adrenal axis, inflammation and disturbances in the basal ganglia circuits) have been suggested (Chaudhuri 2004), factors contributing to fatigue in patients with PD still are not well known (Friedman 2007). It is unlikely that a single mechanism contributes to subjective fatigue (Friedman 2011); this makes it difficult to manage fatigue effectively in patients with PD.

Efforts to manage fatigue usually involve pharmacological and non-pharmacological interventions. A balanced medication regime targeting motor performance (e.g. dopaminergic agents) and mood disturbances (e.g. psychostimulants and antidepressants) combined with a rehabilitation programme (e.g. exercise and cognitive-behavioural therapy) may reduce symptoms of fatigue. Recently, an 'evidence-based medicine review' about treatments for non-motor symptoms of PD (Seppi 2011) included three studies (Lou 2009; Mendonça 2007; Tyne 2010) that investigated the effect of methylphenidate or modafinil on fatigue. Seppi and colleagues concluded that evidence for the efficacy and safety of methylphenidate and modafinil in the treatment of fatigue in PD was insufficient (Seppi 2011). Unfortunately, this review included only study reports published in English, and no attempts were made to aggregate results by conducting a meta-analysis. To our knowledge, the effects of non-pharmacological interventions for fatigue in patients with PD have never been evaluated in a systematic review.

Objectives

To evaluate the effects of pharmacological and non-pharmacological interventions, compared with an inactive control intervention, on subjective fatigue in patients with PD.

Methods

Criteria for considering studies for this review

Types of studies

All types of randomised controlled trials (RCTs) that report on subjective fatigue as an outcome measure are eligible for inclusion. We will not restrict our search on the basis of publication language.

Types of participants

Patients with a clinical diagnosis of PD, as defined by the authors of the RCT.

Types of interventions

Pharmacological interventions

We will include dopaminergic agents (e.g. amantadine, levodopa), psychostimulants (e.g. methylphenidate, modafinil) and antidepressants (e.g. fluoxetine, paroxetine). If further agents are identified for the treatment of fatigue in patients with PD, they will be added to the systematic review.

Non-pharmacological interventions
Exercise

All physical exercise programmes that focus on improvement in exercise capacity and consist of aerobic training and/or strength training.

Cognitive-behavioural therapy

All programmes that focus on behavioural or cognitive aspects to substitute for or alter maladaptive behaviours to manage subjective fatigue.

Other non-pharmacological interventions

If other non-pharmacological interventions are identified for the treatment of fatigue in patients with PD, they will be added to the systematic review.

Control intervention

All experimental interventions should be compared with an inactive control intervention (i.e. placebo, no treatment, standard care, or a waiting list control).

Types of outcome measures

Primary outcomes

Primary outcomes for this systematic review are subjective fatigue, subjective physical fatigue and subjective mental fatigue as measured by self-report questionnaires. If possible, we will categorise the theoretical construct of fatigue as measured by a questionnaire as 'impact of fatigue on daily life' or 'fatigue severity' (Elbers 2012).

We will examine the numbers of adverse events (i.e. anxiety, falls, headache, hypertension, impulse control disorders, life-threatening skin conditions, nausea, orthostatic hypotension, psychosis, suicidal ideation and tachycardia).

Secondary outcomes

Secondary outcomes include depression, HRQOL and sleep disturbances.

Main outcomes for summary of findings table

The following outcomes are selected for the summary of findings table.

  • Subjective fatigue, subjective physical fatigue and subjective mental fatigue.

  • Anxiety, falls, headache, hypertension, impulse control disorders, life-threatening skin conditions, nausea, orthostatic hypotension, psychosis, suicidal ideation and tachycardia.

  • HRQOL.

Search methods for identification of studies

Electronic searches

We will search the Cochrane Central Register of Controlled Trials (CENTRAL), and additional searches of MEDLINE, EMBASE, CINAHL, PsycINFO, PEDro and the World Health Organization (WHO) International Clinical Trials Registry Platfom Search Portal (http://apps.who.int/trialsearch) prospective trial register will be conducted using terms for PD and fatigue combined with the Cochrane Highly Sensitive Search Strategy for identifying randomised trials (Lefebvre 2011) (see Appendix 1).

Searching other resources

References of included studies and identified review articles are screened to look for additional studies.

Data collection and analysis

Selection of studies

Two review authors will independently screen titles and abstracts of all studies identified by the search strategy. Irrelevant studies will be discarded. For the remaining studies, full-text papers will be obtained, and two review authors will independently apply the a priori defined selection criteria. Disagreement will be resolved by discussion. If necessary, a third review author will be consulted to make a final decision.

Data extraction and management

A standardised data extraction form will be designed and tested before two review authors independently extract data on (1) characteristics of the study sample (i.e. inclusion/exclusion criteria, number of participants randomly assigned, age, sex, disease severity, disease duration and comorbid conditions); (2) experimental and control interventions (i.e. description of intervention, dosage, frequency and duration of delivery); (3) outcome measures (i.e. description of outcome measures) and (4) results (i.e. number of participants, point estimates and measures of variance, frequency counts for dichotomous variables). One review author will collate and enter all data into Review Manager 5.2 (Review Manager version 5.2, The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark). Disagreement will be resolved by discussion.

Assessment of risk of bias in included studies

The Cochrane Collaboration tool for assessing risk of bias (Higgins 2011a) will be used by two review authors independently to investigate the risk of bias in included studies. Seven domains of study design (i.e. sequence generation, allocation concealment, blinding of participants or personnel, blinding of outcome assessors, incomplete outcome data, selective reporting and other bias) are scored according to predefined criteria (Higgins 2011a) as 'low risk of bias', 'high risk of bias' or 'unclear risk of bias'. Domain blinding will be investigated separately for different outcomes, and the domain incomplete outcome data will be examined separately for the same outcome at different time points. Disagreement will be resolved by discussion. If necessary, a third review author will be consulted to make a final decision.

Measures of treatment effect

Continuous data
(Standardised) mean difference

The treatment effect for each continuous outcome will be expressed as a mean difference (MD) with 95% confidence interval (CI). When continuous outcomes are measured using different self-report questionnaires, the treatment effect will be expressed as a standardised mean difference (SMD) with 95% CI. We will use postintervention data to calculate the MD and the SMD (Higgins 2011b).

Minimal important difference units

The minimal important difference (MID) represents the smallest change in score in the outcome of interest—beneficial or harmful—that is considered relevant by patients and would lead patients or clinicians to consider a change in management (Jaeschke 1989). If the MID has been established for self-report questionnaires, results can be reported in MID units (i.e. the MD divided by the MID) (Johnston 2010). Standardisation using MIDs may indicate whether the observed effect is considered important by patients and thus may assist clinicians in interpreting the magnitude of an effect size. Therefore, for outcomes presented in the summary of findings table (i.e. self-report fatigue and HRQOL) and measured with an instrument with established MID values in patients with PD, the treatment effect will be calculated in MID units with 95% CI (Johnston 2010).

To obtain MID values, an additional search will be conducted in MEDLINE, EMBASE, CINAHL and PsycINFO. Text words and MESH terms for fatigue, HRQOL and PD are combined with a sensitive filter (designed for PubMed) to identify studies on measurement properties of self-report questionnaires (Terwee 2009) (see Appendix 2). References of included studies and identified review articles are screened for additional articles. Two review authors will independently screen all titles and abstracts identified by the search strategy to look for studies that evaluated measurement properties of self-report fatigue questionnaires or HRQOL instruments in patients with PD and will extract data on (1) the MID value; (2) methods used to establish the MID (i.e. anchor-based or distrubution-based) and (3) standard error of measurement (SEM). The quality of the evidence supporting established MID values will be taken into account, as MID values determined by methods that rely on patient-based and clinical anchors are preferred above MID values determined by distribution-based methods (Revicki 2008). If no published MID values are available, but a measure of variance (i.e. SEM) is available, the SEM will be used to calculate the smallest detectable change (SDC) as a value for a distribution-based MID. The SDC is calculated by 1.96 × √2 × SEM (De Vet 2006).

Dichotomous data

The treatment effect for each dichotomous outcome will be expressed as a risk ratio (RR) or as a risk difference (RD) with 95% CI.

Unit of analysis issues

Cluster-randomised trials

We will use data from cluster-randomised trials if statistical methods were applied to account for clustering in the data (e.g. multi-level analysis, random coefficient analysis, variance component analysis, generalised estimating equations).

Cross-over trials

To avoid possible carry-over effects in cross-over trials, we will use only first period data for analysis.

Studies with multiple treatment groups

We will combine data from relevant experimental intervention groups and relevant control intervention groups to create a single pair-wise comparison.

Dealing with missing data

We will contact investigators to obtain missing data. No statistical methods are used to impute missing data. The potential impact of missing data on the findings of the systematic review will be discussed.

Assessment of heterogeneity

Heterogeneity will be investigated by comparing clinical characteristics such as participant characteristics, types of interventions and outcome measures. We will discuss clinical homogeneity, and based on this discussion, we will decide whether pooling of data is sensible. Statistical heterogeneity is first assessed by visual inspection of the forest plot. We will apply the Chi2 test for homogeneity and will calculate the I2 statistic. To increase the power of the test for homogeneity, we will use a P value < 0.1 in rejecting the null hypothesis of homogeneity. Thresholds for interpretation of the I2 statistic are classified according to the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2011).

  • 0% to 40%: might not be important.

  • 30% to 60%: may represent moderate heterogeneity.

  • 50% to 90%: may represent substantial heterogeneity.

  • 75% to 100%: shows considerable heterogeneity.

When interpreting the results of the test for homogeneity and the I2 statistic, we will take into account the size of the studies included in the meta-analysis. If statistical heterogeneity is observed (Chi2 test P value < 0.1 and I2 statistic > 30%), we will explore factors, other than predefined subgroups, that can explain heterogeneity, such as clinical or methodological characteristics of studies.

Data synthesis

If studies are comparable in relation to participants, interventions and outcomes, data will be combined in a meta-analysis. For continuous outcome variables, a weighted MD or a weighted SMD and if possible a weighted MID (Johnston 2010) will be calculated with a 95% CI, using the inverse variance method. For dichotomous outcomes, we will estimate a pooled RR or RD with a 95% CI using the Mantel-Haenszel method.

We hypothesised that individual studies that evaluated the effects of pharmacological or non-pharmacological interventions may contain different, but related, real effects per study; therefore we will combine results using a random-effects model.

Subgroup analysis and investigation of heterogeneity

We plan to carry out the following subgroup analyses: (1) depressed versus non-depressed participants and (2) participants with pronounced physical fatigue versus participants with pronounced mental fatigue.

Sensitivity analysis

Random-effects model

If a limited number of studies (< five) is included in any meta-analysis, we will use a fixed-effect model to test the robustness of the random-effects model.

Risk of bias

To test the robustness of results, three key domains of the risk of bias assessment (i.e. allocation concealment, blinding of outcome assessment and incomplete outcome data) are used to perform sensitivity analyses. Studies are excluded from the sensitivity analysis when they score 'unclear' or 'high risk of bias' on one of these domains. If blinding of participants is not possible because of the nature of the intervention, we will not consider detection bias for patient-reported outcomes as a criterion for sensitivity analysis.

Quality of the evidence

The quality of the body of evidence will be evaluated using the GRADE system (Schünemann 2011). Results of an RCT are considered as 'high-level' evidence. The level of evidence may decrease on the basis of potential risk of bias of the included studies, indirectness of evidence, unexplained heterogeneity or inconsistency in results, imprecision of results or high probability of publication bias (Schünemann 2011).

To facilitate interpretation of the magnitude of effects, guidance will be provided. A weighted SMD of 0.2 represents a small difference, 0.5 a moderate difference and 0.8 a large difference (Cohen 1988). A weighted MID greater than 1.0 suggests that many patients gain important benefits from treatment, between 0.5 and 1.0 suggests that treatment may benefit an appreciable number of patients and a weighted MID smaller than 0.5 suggests that it is less likely that an appreciable number of patients will achieve important benefits from treatment (Johnston 2010).

Acknowledgements

The review authors would like to thank AP Moore, from The Walton Centre NHS Foundation Trust, for his valuable comments regarding the protocol.

Appendices

Appendix 1. Electronic searches

CENTRAL (through The Cochrane Library)

#1 MeSH descriptor Parkinsonian Disorders explode all trees OR parkinson*

#2 MeSH descriptor Fatigue explode all trees OR MeSH descriptor Muscle Fatigue explode all trees OR MeSH descriptor Fatigue Syndrome, Chronic explode all trees OR fatigue OR lassitude OR tired* OR exhaust* OR weariness OR weary

#3 (#1 AND #2)

MEDLINE (through PubMed)

#1 "parkinsonian disorders"[Mesh] OR "parkinson disease"[Mesh] OR parkinsonian disorders[tiab] OR parkinsonism[tiab] OR parkinson[tiab] OR parkinson disease[tiab] OR parkinsons disease[tiab] OR parkinson's disease[tiab] OR idiopathic parkinson disease[tiab] OR idiopathic parkinsons disease[tiab] OR idiopathic parkinson's disease[tiab]

#2 "fatigue"[Mesh] OR "fatigue syndrome, chronic"[Mesh] OR fatigue[tiab] OR lassitude[tiab] OR tired*[tiab] OR exhaust*[tiab] OR weariness[tiab] OR weary[tiab]

#3 (randomized controlled trial[pt] OR controlled clinical trial[pt] OR randomized[tiab] OR placebo[tiab] OR drug therapy[sh] OR randomly[tiab] OR trial[tiab] OR groups[tiab]) NOT (animals[Mesh] NOT (animals[Mesh] AND humans [Mesh]))

#4 (#1 AND #2 AND #3)

EMBASE (through Ovid)

#1 exp parkinson disease/ OR exp parkinsonism/ OR parkinsonian disorders.ti,ab. OR parkinsonism.ti,ab. OR parkinson.ti,ab. OR parkinson disease.ti,ab. OR parkinsons disease.ti,ab. OR parkinson's disease.ti,ab. OR idiopathic parkinson disease.ti,ab. OR idiopathic parkinsons disease.ti,ab. OR idiopathic parkinson's disease.ti,ab.

#2 exp fatigue/ OR exp chronic fatigue syndrome/ OR fatigue.ti,ab. OR lassitude.ti,ab. OR tired$.ti,ab. OR exhaust$.ti,ab. OR weariness.ti,ab. OR weary.ti,ab.

#3 randomized controlled trial/ OR randomization/ OR controlled study/ OR clinical trial/ OR controlled clinical trial/ OR double blind procedure/ OR single blind procedure/ OR crossover procedure/ OR ((clinica$ adj3 trial$).mp) OR (((singl$ or doubl$ or trebl$ or tripl$) adj3 (mask$ or blind$ or method$)).mp.) OR exp placebo/ OR placebo$.mp. OR random$.mp. OR (((control$ or prospectiv$) adj3 (trial$ or method$ or stud$)).mp.) OR ((crossover$ or cross-over$).mp.)

#4 (#1 AND #2 AND #3)

CINAHL (through EBSCO)

#1 MH"parkinson disease" OR parkinsonian disorders OR parkinsonism OR parkinson OR parkinson disease OR parkinsons disease OR parkinson’s disease OR idiopathic parkinson disease OR idiopathic parkinsons disease OR idiopathic parkinson’s disease

#2 MH"fatigue+" OR fatigue OR lassitude OR tired* OR exhaust* OR weariness OR weary

#3 MH"clinical trials+" OR randomized OR randomised OR placebo OR randomly OR (clinical* AND (trial* OR study OR studies)) OR ((single* OR double* OR triple*) AND blind*)

#4 (#1 AND #2 AND #3)

PsycINFO (through Ovid)

#1 exp parkinsons disease/ OR exp parkinsonism/ OR parkinsonian disorders.ti,ab. OR parkinsonism.ti,ab. OR parkinson.ti,ab. OR parkinson disease.ti,ab. OR parkinsons disease.ti,ab. OR parkinson's disease.ti,ab. OR idiopathic parkinson disease.ti,ab. OR idiopathic parkinsons disease.ti,ab. OR idiopathic parkinson's disease.ti,ab.

#2 exp fatigue/ OR exp chronic fatigue syndrome/ OR fatigue.ti,ab. OR lassitude.ti,ab. OR tired$.ti,ab. OR exhaust$.ti,ab. OR weariness.ti,ab. OR weary.ti,ab.

#3 randomized controlled trial/ OR randomization/ OR controlled study/ OR clinical trial/ OR controlled clinical trial/ OR double blind procedure/ OR single blind procedure/ OR crossover procedure/ OR ((clinica$ adj3 trial$).mp) OR (((singl$ or doubl$ or trebl$ or tripl$) adj3 (mask$ or blind$ or method$)).mp.) OR exp placebo/ OR placebo$.mp. OR random$.mp. OR (((control$ or prospectiv$) adj3 (trial$ or method$ or stud$)).mp.) OR ((crossover$ or cross-over$).mp.)

#4 (#1 AND #2 AND #3)

PEDro (http://search.pedro.org.au/pedro/basic_findrecords.php?-type=new_search)

#1 parkinson

#2 fatigue

#3 (#1 AND #2)

WHO International Clinical Trials Registry Platform Search Portal (http://apps.who.int/trialsearch)

#1 parkinson

#2 fatigue

#3 (#1 AND #2)

Appendix 2. Additional search strategy to identify studies on measurement properties

MEDLINE (through PubMed)

#1 "parkinsonian disorders"[Mesh] OR "parkinson disease"[Mesh] OR parkinsonian disorders[tiab] OR parkinsonism[tiab] OR parkinson[tiab] OR parkinson disease[tiab] OR parkinsons disease[tiab] OR parkinson's disease[tiab] OR idiopathic parkinson disease[tiab] OR idiopathic parkinsons disease[tiab] OR idiopathic parkinson's disease[tiab]

#2 "fatigue"[Mesh] OR "fatigue syndrome, chronic"[Mesh] OR fatigue[tiab] OR lassitude[tiab] OR tired*[tiab] OR exhaust*[tiab] OR weariness[tiab] OR weary[tiab]

#3 "quality of life"[Mesh] OR "value of life"[Mesh] OR "quality of life"[tiab] OR "health related"[tiab] OR health-related[tiab] OR qol[tiab] OR hrqol[tiab] OR hr-qol[tiab] OR hrql[tiab]

#4 (#2 OR #3)

#5 (#1 AND #4)

#6 instrumentation[sh] OR methods[sh] OR validation studies[pt] OR comparative study[pt] OR "psychometrics"[Mesh] OR psychometr*[tiab] OR clinimetr*[tw] OR clinometr*[tw] OR "outcome assessment (health care)"[Mesh] OR outcome assessment[tiab] OR outcome measure*[tw] OR "observer variation"[Mesh] OR observer variation[tiab] OR "health status indicators"[Mesh] OR "reproducibility of results"[Mesh] OR reproducib*[tiab] OR "discriminant analysis"[Mesh] OR reliab*[tiab] OR unreliab*[tiab] OR valid*[tiab] OR coefficient[tiab] OR homogeneity[tiab] OR homogeneous[tiab] OR "internal consistency"[tiab] OR (cronbach*[tiab] AND (alpha[tiab] OR alphas[tiab])) OR (item[tiab] AND (correlation*[tiab] OR selection*[tiab] OR reduction*[tiab])) OR agreement[tiab] OR precision[tiab] OR imprecision[tiab] OR "precise values"[tiab] OR test retest[tiab] OR (test[tiab] AND retest[tiab]) OR (reliab*[tiab] AND (test[tiab] OR retest[tiab])) OR stability[tiab] OR interrater[tiab] OR inter-rater[tiab] OR intrarater[tiab] OR intra-rater[tiab] OR intertester[tiab] OR inter-tester[tiab] OR intratester[tiab] OR intra-tester[tiab] OR interobserver[tiab] OR inter-observer[tiab] OR intraobserver[tiab] OR intraobserver[tiab] OR intertechnician[tiab] OR inter-technician[tiab] OR intratechnician[tiab] OR intra-technician[tiab] OR interexaminer[tiab] OR inter-examiner[tiab] OR intraexaminer[tiab] OR intra-examiner[tiab] OR interassay[tiab] OR inter-assay[tiab] OR intraassay[tiab] OR intra-assay[tiab] OR interindividual[tiab] OR inter-individual[tiab] OR intraindividual[tiab] OR intra-individual[tiab] OR interparticipant[tiab] OR inter-participant[tiab] OR intraparticipant[tiab] OR intra-participant[tiab] OR kappa[tiab] OR kappas[tiab] OR kappas[tiab] OR repeatab*[tiab] OR ((replicab*[tiab] OR repeated[tiab]) AND (measure[tiab] OR measures[tiab] OR findings[tiab] OR result[tiab] OR results[tiab] OR test[tiab] OR tests[tiab])) OR generaliza*[tiab] OR generalisa*[tiab] OR concordance[tiab] OR (intraclass[tiab] AND correlation*[tiab]) OR discriminative[tiab] OR "known group"[tiab] OR factor analysis[tiab] OR factor analyses[tiab] OR dimension*[tiab] OR subscale*[tiab] OR (multitrait[tiab] AND scaling[tiab] AND (analysis[tiab] OR analyses[tiab])) OR item discriminant[tiab] OR interscale correlation*[tiab] OR error[tiab] OR errors[tiab] OR "individual variability"[tiab] OR (variability[tiab] AND (analysis[tiab] OR values[tiab])) OR (uncertainty[tiab] AND (measurement[tiab] OR measuring[tiab])) OR "standard error of measurement"[tiab] OR sensitiv*[tiab] OR responsive*[tiab] OR ((minimal[tiab] OR minimally[tiab] OR clinical[tiab] OR clinically[tiab]) AND (important[tiab] OR significant[tiab] OR detectable[tiab]) AND (change[tiab] OR difference[tiab])) OR (small*[tiab] AND (real[tiab] OR detectable[tiab]) AND (change[tiab] OR difference[tiab])) OR meaningful change[tiab] OR "ceiling effect"[tiab] OR "floor effect"[tiab] OR "item response model"[tiab] OR IRT[tiab] OR rasch[tiab] OR "differential item functioning"[tiab] OR DIF[tiab] OR "computer adaptive testing"[tiab] OR "item bank"[tiab] OR "cross-cultural equivalence"[tiab]

#7 (#5 AND #6)

EMBASE (through Ovid)

#1 exp parkinson disease/ OR exp parkinsonism/ OR parkinsonian disorders.ti,ab. OR parkinsonism.ti,ab. OR parkinson.ti,ab. OR parkinson disease.ti,ab. OR parkinsons disease.ti,ab. OR parkinson's disease.ti,ab. OR idiopathic parkinson disease.ti,ab. OR idiopathic parkinsons disease.ti,ab. OR idiopathic parkinson's disease.ti,ab.

#2 exp fatigue/ OR exp chronic fatigue syndrome/ OR fatigue.ti,ab. OR lassitude.ti,ab. OR tired$.ti,ab. OR exhaust$.ti,ab. OR weariness.ti,ab. OR weary.ti,ab.

#3 exp quality of life/ OR exp health related quality of life/ OR exp hrql/ OR exp life quality/ OR "quality of life".ti,ab. OR "health related".ti,ab. OR health-related.ti,ab. OR qol.ti,ab. OR hrqol.ti,ab. OR hr-qol.ti,ab. OR hrql.ti,ab.

#4 (#2 OR #3)

#5 (#1 AND #4)

#6 exp psychometry/ OR exp outcome assessment/ OR exp reliability/ OR exp cronbach alpha coefficient/ OR exp internal consistency/ OR exp interrater reliability/ OR exp intrarater reliability/ OR exp item total correlation/ OR exp kuder richardson coefficient/ OR exp split half correlation/ OR exp test retest reliability/ OR exp validity/ OR exp concurrent validity/ OR exp construct validity/ OR exp content validity/ OR exp criterion related validity/ OR exp discriminant validity/ OR exp face validity/ OR exp multitrait multimethod/ OR exp observer variation/ OR exp health survey/ OR exp reproducibility/ OR exp discriminant analysis/ OR exp rating scale/ OR psychometr$.ti,ab. OR clinimetr$.ti,ab. OR clinometr$.ti,ab. OR outcome assessment.ti,ab. OR outcome measure$.ti,ab. OR observer variation.ti,ab. OR reproducib$.ti,ab. OR reliab$.ti,ab. or unreliab$.ti,ab. OR valid$.ti,ab. OR coefficient.ti,ab. OR homogeneity.ti,ab. OR homogeneous.ti,ab. OR "internal consistency".ti,ab. OR (cronbach$ AND (alpha OR alphas)).ti,ab. OR (item AND (correlation$ OR selection$ OR reduction$)).ti,ab. OR agreement.ti,ab. OR precision.ti,ab. OR imprecision.ti,ab. OR "precise values".ti,ab. OR test retest.ti,ab. OR (test AND retest).ti,ab. OR (reliab$ AND (test OR retest)).ti,ab. OR stability.ti,ab. OR interrater.ti,ab. OR inter-rater.ti,ab. OR intrarater.ti,ab. OR intra-rater.ti,ab. OR intertester.ti,ab. OR inter-tester.ti,ab. OR intratester.ti,ab. OR intra-tester.ti,ab. OR interobserver.ti,ab. OR inter-observer.ti,ab. OR intraobserver.ti,ab. OR intraobserver.ti,ab. OR intertechnician.ti,ab. OR inter-technician.ti,ab. OR intratechnician.ti,ab. OR intra-technician.ti,ab. OR interexaminer.ti,ab. OR inter-examiner.ti,ab. OR intraexaminer.ti,ab. OR intra-examiner.ti,ab. OR interassay.ti,ab. OR inter-assay.ti,ab. OR intraassay.ti,ab. OR intra-assay.ti,ab. OR interindividual.ti,ab. OR inter-individual.ti,ab. OR intraindividual.ti,ab. OR intra-individual.ti,ab. OR interparticipant.ti,ab. OR inter-participant.ti,ab. OR intraparticipant.ti,ab. OR intra-participant.ti,ab. OR kappa.ti,ab. OR kappas.ti,ab. OR kappas.ti,ab. OR repeatab$.ti,ab. OR ((replicab$OR repeated) AND (measure OR measures OR findings OR result OR results OR test OR tests)).ti,ab. OR generaliza$.ti,ab. OR generalisa$.ti,ab. OR concordance.ti,ab. OR (intraclass and correlation$).ti,ab. OR discriminative.ti,ab. OR "known group".ti,ab. OR factor analysis.ti,ab. OR factor analyses.ti,ab. OR dimension$.ti,ab. OR subscale$.ti,ab. OR (multitrait AND scaling AND (analysis OR analyses)).ti,ab. OR item discriminant.ti,ab. OR interscale correlation$.ti,ab. OR error.ti,ab. OR errors.ti,ab. OR "individual variability".ti,ab. OR (variability AND (analysis OR values)).ti,ab. OR (uncertainty AND (measurement OR measuring)).ti,ab. OR "standard error of measurement".ti,ab. OR sensitiv$.ti,ab. OR responsive$.ti,ab. OR ((minimal OR minimally OR clinical OR clinically) AND (important OR significant OR detectable) AND (change OR difference)).ti,ab. OR (small$ AND (real OR detectable) AND (change OR difference)).ti,ab. OR meaningful change.ti,ab. OR "ceiling effect".ti,ab. OR "floor effect".ti,ab. OR "item response model".ti,ab. OR IRT.ti,ab. OR rasch.ti,ab. OR "differential item functioning".ti,ab. OR DIF.ti,ab. OR "computer adaptive testing".ti,ab. OR "item bank".ti,ab. OR "cross-cultural equivalence".ti,ab.

#7 (#5 AND #6)

CINAHL (through EBSCO)

#1 MH"parkinson disease" OR parkinsonian disorders OR parkinsonism OR parkinson OR parkinson disease OR parkinsons disease OR parkinson’s disease OR idiopathic parkinson disease OR idiopathic parkinsons disease OR idiopathic parkinson’s disease

#2 MH"fatigue+" OR fatigue OR lassitude OR tired* OR exhaust* OR weariness OR weary

#3 MH"quality of life+" OR "quality of life" OR "health related" OR health-related OR qol OR hrqol OR hr-qol OR hrql

#4 (#2 OR #3)

#5 (#1 AND #4)

#6 MH"research measurement+" OR MH"outcome assessment" OR MH"health status indicators" OR MH"reproducibility of results" OR MH"outcomes research"

#7 (#5 AND #6)

PsycINFO (through Ovid)

#1 exp parkinsons disease/ OR exp parkinsonism/ OR parkinsonian disorders.ti,ab. OR parkinsonism.ti,ab. OR parkinson.ti,ab. OR parkinson disease.ti,ab. OR parkinsons disease.ti,ab. OR parkinson's disease.ti,ab. OR idiopathic parkinson disease.ti,ab. OR idiopathic parkinsons disease.ti,ab. OR idiopathic parkinson's disease.ti,ab.

#2 exp fatigue/ OR exp chronic fatigue syndrome/ OR fatigue.ti,ab. OR lassitude.ti,ab. OR tired$.ti,ab. OR exhaust$.ti,ab. OR weariness.ti,ab. OR weary.ti,ab.

#3 exp quality of life/ OR exp life satisfaction/ OR "quality of life".ti,ab. OR "health related".ti,ab. OR health-related.ti,ab. OR qol.ti,ab. OR hrqol.ti,ab. OR hr-qol.ti,ab. OR hrql.ti,ab.

#4 (#2 OR #3)

#5 (#1 AND #4)

#6 exp psychometrics/ OR exp classical test theory/ OR exp item response theory/ OR exp test validity/ OR exp test reliability/ OR exp error of measurement/ OR exp test construction/ OR exp internal consistency/ OR exp interrater reliability/ OR exp rating scales/ OR exp measurement/ OR psychometr$.ti,ab. OR clinimetr$.ti,ab. OR clinometr$.ti,ab. OR outcome assessment.ti,ab. OR outcome measure$.ti,ab. OR observer variation.ti,ab. OR reproducib$.ti,ab. OR reliab$.ti,ab. or unreliab$.ti,ab. OR valid$.ti,ab. OR coefficient.ti,ab. OR homogeneity.ti,ab. OR homogeneous.ti,ab. OR "internal consistency".ti,ab. OR (cronbach$ AND (alpha OR alphas)).ti,ab. OR (item AND (correlation$ OR selection$ OR reduction$)).ti,ab. OR agreement.ti,ab. OR precision.ti,ab. OR imprecision.ti,ab. OR "precise values".ti,ab. OR test retest.ti,ab. OR (test AND retest).ti,ab. OR (reliab$ AND (test OR retest)).ti,ab. OR stability.ti,ab. OR interrater.ti,ab. OR inter-rater.ti,ab. OR intrarater.ti,ab. OR intra-rater.ti,ab. OR intertester.ti,ab. OR inter-tester.ti,ab. OR intratester.ti,ab. OR intra-tester.ti,ab. OR interobserver.ti,ab. OR inter-observer.ti,ab. OR intraobserver.ti,ab. OR intraobserver.ti,ab. OR intertechnician.ti,ab. OR inter-technician.ti,ab. OR intratechnician.ti,ab. OR intra-technician.ti,ab. OR interexaminer.ti,ab. OR inter-examiner.ti,ab. OR intraexaminer.ti,ab. OR intra-examiner.ti,ab. OR interassay.ti,ab. OR inter-assay.ti,ab. OR intraassay.ti,ab. OR intra-assay.ti,ab. OR interindividual.ti,ab. OR inter-individual.ti,ab. OR intraindividual.ti,ab. OR intra-individual.ti,ab. OR interparticipant.ti,ab. OR inter-participant.ti,ab. OR intraparticipant.ti,ab. OR intra-participant.ti,ab. OR kappa.ti,ab. OR kappas.ti,ab. OR kappas.ti,ab. OR repeatab$.ti,ab. OR ((replicab$OR repeated) AND (measure OR measures OR findings OR result OR results OR test OR tests)).ti,ab. OR generaliza$.ti,ab. OR generalisa$.ti,ab. OR concordance.ti,ab. OR (intraclass and correlation$).ti,ab. OR discriminative.ti,ab. OR "known group".ti,ab. OR factor analysis.ti,ab. OR factor analyses.ti,ab. OR dimension$.ti,ab. OR subscale$.ti,ab. OR (multitrait AND scaling AND (analysis OR analyses)).ti,ab. OR item discriminant.ti,ab. OR interscale correlation$.ti,ab. OR error.ti,ab. OR errors.ti,ab. OR "individual variability".ti,ab. OR (variability AND (analysis OR values)).ti,ab. OR (uncertainty AND (measurement OR measuring)).ti,ab. OR "standard error of measurement".ti,ab. OR sensitiv$.ti,ab. OR responsive$.ti,ab. OR ((minimal OR minimally OR clinical OR clinically) AND (important OR significant OR detectable) AND (change OR difference)).ti,ab. OR (small$ AND (real OR detectable) AND (change OR difference)).ti,ab. OR meaningful change.ti,ab. OR "ceiling effect".ti,ab. OR "floor effect".ti,ab. OR "item response model".ti,ab. OR IRT.ti,ab. OR rasch.ti,ab. OR "differential item functioning".ti,ab. OR DIF.ti,ab. OR "computer adaptive testing".ti,ab. OR "item bank".ti,ab. OR "cross-cultural equivalence".ti,ab.

#7 (#5 AND #6)

Contributions of authors

  • Conceptualisation of project: Roy G Elbers, Erwin EH van Wegen, John Verhoef and Gert Kwakkel.

  • Design and writing of draft: Roy G Elbers.

  • Review and critique of draft: Erwin EH van Wegen, John Verhoef, Henk W Berendse and Gert Kwakkel.

Declarations of interest

None known.

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