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Original Research

Assessing Frailty with the Tilburg Frailty Indicator (TFI): A Review of Reliability and Validity

ORCID Icon & ORCID Icon
Pages 863-875 | Published online: 18 May 2021

Abstract

Objective

The Tilburg Frailty Instrument (TFI) is an instrument for assessing frailty in community-dwelling older people. Since its development, many studies have been carried out examining the psychometric properties. The aim of this study was to provide a review of the main findings with regard to the reliability and validity of the TFI.

Methods

We conducted a literature search in the PubMed and CINAHL databases on May 30, 2020. An inclusion criterion was the use of the entire TFI, part B, referring to the 15 components. No restrictions were placed on language or year of publication.

Results

In total, 27 studies reported about the psychometric properties of the TFI. By far, most of the studies (n = 25) were focused on community-dwelling older people. Many studies showed that the internal consistency and test–retest reliability are good, which also applies for the criterion and construct validity. In many studies, adverse outcomes of interest were disability, increased health-care utilization, lower quality of life, and mortality. Regarding disability, studies predominantly show results that are excellent, with an area under the curve (AUC) >0.80. In addition, the TFI showed good associations with lower quality of life and the findings concerning mortality were at least acceptable. However, the association of the TFI with some indicators of health-care utilization can be indicated as poor (eg, visits to a general practitioner, hospitalization).

Conclusion

Since population aging is occurring all over the world, it is important that the TFI is available and well known that it is a user-friendly instrument for assessing frailty and its psychometric properties being qualified as good. The findings of this assessment can support health-care professionals in selecting interventions to reduce frailty and delay its adverse outcomes, such as disability and lower quality of life.

Introduction

The Tilburg Frailty Instrument (TFI) is an instrument for assessing frailty in community-dwelling older people. It has been developed as a self-report instrument in that older people have to complete the TFI themselves.Citation1 The TFI is based on the following conceptual definition of frailty: ‘frailty is a dynamic state affecting an individual who experiences losses in one or more domains of human functioning (physical, psychological and social), which is caused by the influence of a range of variables and increases the risk of adverse outcomes’.Citation2 Both the conceptual definition of frailty and the TFI derived from it consider frailty as a multidimensional concept, including physical, psychological and social functioning of older people, and emphasize the importance of an integral approach to human functioning. The World Health Organization recommends this holistic approach to take care of frail, older people.Citation3 Paying sole attention to physical frailty can lead to fragmentation of careCitation2,Citation4 and possibly to a reduction of the quality of care and a decrease in the experienced quality of life in frail older people. According to Gilardi et al, a multidimensional approach to frailty can be more effective to plan and implement care services, as well as establish prevention programs for frail older people.Citation5

The TFI contains two parts: part A, on 10 determinants of frailty, and part B, on 15 components of frailty.Citation1 The determinants are sex, age, marital status, education, income, ethnicity, lifestyle, life events, multimorbidity and living environment. The components of frailty refer to physical frailty (eight), psychological frailty (four) and social frailty (three). Physical frailty includes physically unhealthy, unexplained weight loss, difficulty walking, difficulty maintaining balance, poor hearing, poor vision, lack of strength in the hands and physical tiredness. Psychological frailty consists of the components of memory problems, feeling down, feeling nervous or anxious and unable to cope with problems. Social frailty includes living alone, lack of social relations and lack of social support. The total score of the TFI is 0–15, with a score ranging from 0 to 8 for physical frailty, 0 to 4 for psychological frailty and 0 to 4 for social frailty. Higher scores refer to greater frailty, as older persons with a total TFI score ≥5 are considered to be frail.Citation1

Originally, the TFI was developed in the Netherlands by Gobbens et al and based on an extensive literature search and opinions of an international group of frailty experts, including geriatricians, gerontologists, nurses and psychologists.Citation6 Their first study examined the psychometric properties of the TFI in two Dutch samples of community-dwelling persons aged 75 years and older.Citation1 Subsequently, the TFI was translated into several languages, including Brazilian Portuguese,Citation7 Danish,Citation8 Italian,Citation9 Portuguese,Citation10 Polish,Citation11 German,Citation12 Chinese,Citation13 Spanish,Citation14 and Turkish.Citation15 Until now, two systematic reviews and one narrative review have been published, indicating that the TFI is very suitable for assessing frailty among community-dwelling older people.Citation5,Citation16,Citation17 According to Pialoux et al, both the TFICitation1 and the SHARE Frailty IndexCitation18 are potentially suitable for screening frailty in older people in primary care settings.Citation16 Sutton et al concluded that the TFI has the most robust evidence of reliability and validity of 38 frailty assessment instruments, including frequently used instruments, such as the Phenotype of FrailtyCitation19 and the Frailty Index.Citation17 In addition, the narrative review by Gilardi et al identified the TFI as the best screening instrument to use in public health because it was the only one of the selected instruments (including the Phenotype of Frailty,Citation19 Vulnerable Elders Survey,Citation20 Frailty Index,Citation21 and the SHARE Frailty Index)Citation18 with three features: a multidimensional structure, quick and easy to use, and an accurate risk prediction of adverse outcomes of frailty.Citation5 In addition, De Witte et al used the TFI as a gold standard for the validation of their instrument, The Comprehensive Frailty Assessment Instrument.Citation22

Since the TFI was developed approximately 10 years ago,Citation1 and many studies into its psychometric properties have been carried out since then,Citation17 this study aims to provide a review of the main findings regarding this issue. We present the reliability and validity of these studies.

Methods

Literature Search

We conducted a literature search in the PubMed and CINAHL databases on May 30, 2020, using “Tilburg Frailty Indicator AND psychometric properties”, “TFI AND psychometric properties”, “Tilburg Frailty Indicator AND validity”, “TFI AND validity”, “Tilburg Frailty Indicator AND reliability”, and “TFI AND reliability”. An inclusion criterion was the use of the entire TFI, part B, referring to the 15 components. No restrictions were placed on language or year of publication. The studies were screened and selected for inclusion by the first author. In total, 27 studies were selected for the purpose of this review.

Reliability and Validity

Reliability

Four types of reliability were distinguished: internal consistency, test-retest, inter-rater reliability, and parallel forms reliability. Internal consistency refers to consistency across items of measurement. Statistical techniques used for this purpose were Cronbach’s alpha, Kuder–Richardson Formula 20 (KR-20) and item correlations. Cronbach’s alpha and KR-20 values >0.70 were considered acceptable.Citation23,Citation24 The higher the item correlations, the better the internal consistency of the measurement instrument.

Test-retest indicates consistency among time (stability). Correlations, simple agreement, kappa (chance-corrected agreement) and intraclass correlation coefficient (ICC) were used to determine test–retest reliability. The higher the correlation, simple agreement, kappa value and ICC, the higher the concordance between the two assessments will be. The correlation coefficient was evaluated using the classification of Callegari-Jacques (weak, <0.30; moderate, 0.30–0.60; strong, 0.60–0.90; very strong, ≥0.90).Citation25 For the interpretation of the Kappa value, we used the Landis and Koch evaluation (absent, <0.10; weak, 0.10–0.20; fair, 0.21–0.40; moderate, 0.41–0.60; substantial, 0.61–0.80; nearly perfect, 0.81–1.00).Citation26 The ICC was evaluated using the guideline provided by Koo and Li (poor <0.50; moderate, 0.50–0.75; good, 0.75–0.90; excellent >0.90).Citation27

Inter-rater reliability concerns consistency across different researchers. Frequently used techniques to establish inter-rater reliability are Kappa and ICC.

The fourth and final type of reliability, parallel forms reliability, assesses the correlation between two equivalent versions of a measurement instrument. High correlation between the two instruments indicates high forms reliability.

Validity

Six types of validity can be distinguished: criterion, construct, content, face, structural, and known-group validity. Criterion validity concerns the relation between the score on a measurement instrument and some external criterion.Citation28 If the measurement instrument corresponds to a criterion assessed simultaneously, the validity is considered concurrent. If the measurement instrument forecasts a criterion value in the future, the validity is labeled predictive.Citation28 Criterion validity can be checked by determining a correlation coefficient and conducting receiver operating characteristics (ROC) curve analyses and calculating the Area Under the Curve (AUC). An AUC <0.7, 0.7–0.8, 0.8–0.9, and ≥0.9, is considered poor (no discrimination), acceptable, excellent, and outstanding, respectively.Citation29

Construct validity refers to the simultaneous process of measure and theory validation.Citation30 Convergent and divergent (discriminant) validities constitute construct validity. Convergent validity involves the degree by which two measures of constructs should be or are related. By contrast, divergent validity indicates whether measures that should be unrelated, are unrelated.Citation31 Correlation tests are performed to establish convergent and divergent validity and thus, construct validity.

Content validity concerns the extent in which a measurement instrument includes all necessary components of the construct to be assessed.Citation32 According to Burns and Grove, content validity is obtained from literature, representatives of the population concerned and experts.Citation33 A measurement instrument has face validity if it appears to assess what it is supposed to assess and that it will work.Citation34 As well as when determining content validity, representatives of the population concerned and experts can be involved; however, establishing face validity is more informal, compared to content validity.

Structural validity refers to the extent to which an instrument covers the hypothetical dimension of a construct.Citation32 According to Souza et al, factorial analysis and structural equation modeling are the appropriate statistical techniques to assess structural validity.Citation35 Finally, known-group validity involves an instrument’s ability to make a distinction between groups. Group differences can be determined using a chi-square test and t-test. When describing the findings on the reliability and validity of the TFI in the included studies, the classification described above has been used foremost.

Results

Characteristics of the Studies

presents the characteristics of the 27 included studies. The first studies were performed in 2010.Citation1,Citation36 Thirteen studies were carried out in the Netherlands,Citation1,Citation36Citation47 of which two were part of a large study that also collected data in other European countries.Citation46,Citation47 Three studies were exclusively conducted in Denmark,Citation8,Citation48,Citation49 and two in PolandCitation11,Citation50 and Brazil.Citation7,Citation51 By far, most of the studies were conducted among community-dwelling older people. Two exceptions were studies including older Danish people admitted to a hospitalCitation49 and one study evaluating older Dutch residents of assisted living facilities.Citation39 Two-thirds of the studies used a cross-sectional design, two of which were qualitative studies conducted in Denmark,Citation8,Citation48 and the other studies were characterized by a longitudinal design. The sample size varied from 14 to 27,527 people.Citation46,Citation48 The most commonly used age groups were people aged ≥65 years (eight studies) and aged ≥70 years (seven studies). One study only showed the mean age of the sample.Citation8 The highest mean age was observed among Dutch people residing at assisted living facilities (84.8 years).Citation39

Table 1 General Characteristics of the Studies Included

Using the original TFI cut-off point of 5,Citation1 prevalence figures concerning the general population of community-dwelling older people ranged from 12.4% to 47.1% in samples of Chinese and Dutch individuals.Citation1,Citation13 Specifically, prevalence was higher among Turkish people admitted to a geriatrics outpatient clinic (63.6%),Citation15 residents of assisted living facilities (76.5%)Citation39 and among physical pre-frail and frail community-dwelling older people (64.8%).Citation43 In the latter group, the frailty status of the participants was first assessed by the Phenotype of Frailty.Citation19 Among community-dwelling older people, the prevalence of frailty was highest in a sample of Portuguese people (54.8%), while the cut-off point was 6.Citation10 It should be noted that seven studies did not present a prevalence figure of frailty.Citation8,Citation14,Citation41,Citation42,Citation44,Citation47,Citation48 A Dutch sample including 479/484 participants and a Dutch sample consisting of 2420 participants were used in threeCitation1,Citation41,Citation42 and two studies,Citation43,Citation44 respectively. Moreover, two other Dutch studies partially used the same sample.Citation36,Citation37 Additional details are displayed in .

Reliability of the TFI

In total,16 studies report the reliability of the TFI. The four types of reliability observed were internal consistency, test–retest, inter-rater and parallel forms reliability. Fifteen studies determined the internal consistency reliability and one study failed to do so (see ).Citation46 The Cronbach’s alpha for the TFI total was 0.66 (lowest)Citation9 to 0.80 (highest),Citation45 whereas the KR-20, calculated in three studies was 0.69, 0.70 and 0.78.Citation10,Citation14,Citation52 Eight studies also present the Cronbach’s alpha for physical, psychological and social frailty, ranging from 0.57 to 0.79,Citation7,Citation9 0.37 to 0.63,Citation1,Citation50 and 0.25 to 0.59,Citation13,Citation50 respectively. The lowest and highest values of the KR-20, with regard to physical, psychological, and social frailty, were 0.64Citation14 and 0.75,Citation10 0.48Citation10 and 0.58,Citation14 and 0.22Citation14 and 0.49,Citation10 respectively. Six studies examined the internal consistency reliability of the TFI using corrected item-total correlations.Citation9,Citation12,Citation15,Citation36,Citation50,Citation52

Table 2 Internal Consistency Reliability of the TFI

Test–retest reliability was observed in nine studies, using Pearson correlations,Citation1,Citation7,Citation10 Kappa,Citation7,Citation10,Citation14,Citation50 simple agreement,Citation7,Citation10,Citation14 and ICCCitation12,Citation13,Citation15,Citation52 (see ). Pearson correlations, with regard to frailty total were 0.88,Citation7 0.90,Citation1 and 0.91,Citation10 using a period less than 3 weeks. The Pearson correlation coefficient was 0.79 for a 1-year period.Citation1 The correlation coefficients, with respect to the frailty domains, are detailed in . Using Kappa, the level of agreement varied greatly at item level.Citation7,Citation10,Citation14,Citation50 Obviously, the level of agreement was higher when the simple agreement technique was usedCitation7,Citation10,Citation14 (displayed in ). For frailty total, the ICC ranged from 0.86 to 0.99Citation15,Citation52 in two studies involving a follow-up period of 1 week.

Table 3 Test–Retest Reliability, Inter-Rater Reliability, and Parallel Forms Reliability of the TFI

also shows the inter-rater and parallel forms reliability of the TFI. Inter-rater reliability was identified in only one study in which, on the same day, two observers came to almost perfect agreement (ICC = 0.99).Citation15 Finally, in two studies, parallel forms reliability was determined.Citation13,Citation46 One of these studies examined the agreement between the TFI (frailty total) and other validated frailty instruments. The highest agreement existed with the Frailty Index (FI) and the Comprehensive Geriatric Assessment and less agreement was found with the Edmonton Frail Scale and the Frail scale.Citation46 The other study used Kappa to establish the level of agreement between TFI items and alternative measures resulting in low and high levels of agreement (0.12 for hearing problems and 1.00 for living alone).Citation13

Validity of the TFI

Criterion Validity

show an overview of the validity of the TFI, which includes 24 of the 27 studies. Criterion validity was the most frequently presented type of validity, with concurrent and predictive characteristics reported in 10 and 9 studies, respectively (see ). Concurrent validity was determined using different techniques: correlations, AUC and regression analyses. Frequently occurring adverse outcomes of interest were lower quality of life,Citation1,Citation10,Citation39,Citation40,Citation45 disability,Citation1,Citation9,Citation10,Citation13,Citation39,Citation47 and an increase in health-care utilization.Citation1,Citation9,Citation10,Citation13,Citation39 Using different instruments for assessing quality of life (WHOQOL-BREF,Citation53 WHOQOL-OLDCitation54 and EUROHIS-QOL)Citation55, four included studies demonstrated that higher scores on the TFI were correlated with lower quality of life.Citation1,Citation10,Citation40,Citation45 Regarding disability and referring to limitations in performing activities of daily living (ADL) and/or instrumental activities of daily living (IADL), the AUCs were excellent in three studies,Citation1,Citation9,Citation47 and acceptable for ADL and poor for IADL in two studies.Citation10,Citation13 Many different indicators of health-care utilization were used, eg, visits to a general practitioner, hospitalization and receiving nursing care. In most studies, the findings were poorCitation9,Citation10,Citation13; however, Gobbens et al observed an excellent AUC for reporting personal care, and acceptable AUCs for reporting nursing and informal care.Citation1 Three studies determined the discriminating ability of the TFI to identify frailty with other validated frailty measures using the AUC: the Groningen Frailty Indicator (GFI),Citation10 the phenotype of frailty,Citation10,Citation13 Survey of Health, Ageing and Retirement in Europe-Frailty Instrument (SHARE-FI),Citation47 and the Frailty Index (FI).Citation13 The AUCs for GFI, SHARE-FI and the FI were excellent; however, the AUCs for the phenotype of frailty were not unequivocal. Two studies examined the correlations between the TFI and other frailty measures: the GFI,Citation36 Sherbrooke Postal Questionnaire (SPQ),Citation36 and the Phenotype of Frailty.Citation14 The correlations between the TFI and GFI, SPQ and phenotype of frailty were 0.76, 0.42, and 0.49, respectively.Citation14,Citation36

Table 4 Criterion Validity of the TFI

Table 5 Construct Validity of the TFI

Table 6 Content Validity, Face Validity, Structural Validity, and Known-Groups Validity of the TFI

The predictive validity was established using regression analyses and AUC. The prediction period ranged from 6 monthsCitation49 to 5 years.Citation46 Most studies only used a period of 1 or 2 years.Citation37,Citation38,Citation42Citation44,Citation51 In particular, adverse outcomes of interest were disability,Citation37,Citation38,Citation42Citation44,Citation51 mortality,Citation37,Citation43,Citation46,Citation49,Citation51 increased health-care utilizationCitation37,Citation38,Citation42,Citation43,Citation51 and lower quality of life.Citation41,Citation42 Disability was predicted by the TFI; however, Gobbens et alCitation38,Citation42 indicated that the predictive value was excellent, while Op Het Veld et al concluded that it was poor,Citation43 presenting a positive predictive value of 42.6% and a negative predictive value of 75.2%.Citation44 In four studies, the findings concerning mortality were at least acceptable; only Op Het Veld et al qualified the predictive value of the TFI as poor.Citation43 As with the determination of concurrent validity, many different indicators of health-care utilization were used as outcome variables, resulting in findings that were not unanimous. For instance, the TFI predicted hospitalization in a sample of 430 Dutch people ≥70 years (OR = 2.59, 95% CI = 1.36–4.90),Citation37 in comparison to a poor AUC in a sample of 2420 Dutch people ≥65 years.Citation43 Both studies that aimed to assess the predictive value of the TFI for quality of life provided evidence that the TFI predicts lower quality of life using a follow-up period of 1, 2 and 4 years.Citation41,Citation42

Construct Validity

The reviewed studies frequently determined the criterion validity of the TFI, as well as the construct validity. Ten studies determined the construct validity of the TFI,Citation1,Citation7,Citation9,Citation10,Citation12Citation14,Citation45,Citation47,Citation52 with nine of these studies found to address the issue of convergent and divergent validity, with exception of the study by Renne and Gobbens (see ).Citation45 Most of the studies found the expected correlations between total frailty, domains, items, and alternative measures, while two studies observed similar correlations between the psychological and social domains of the TFI and alternative psychological.Citation10,Citation13 Moreover, the Spanish study demonstrated a stronger correlation between social frailty and IADL, assessed with the Lawton scale, than between social frailty and physical frailty, which was expected.Citation14 Finally, in the Brazilian study, the item coping was not correlated as expected.Citation7

Content and Face Validity

presents the content, face, structural and known-groups validity of the TFI. Three studies determined the content validity of the TFI,Citation1,Citation46,Citation48 showing that the TFI contains the majority of important frailty items. Based on interviews with community-dwelling older people, Andreasen et al argue that items referring sleep quality, pain, spirituality, and meaningful activities should be included in the TFI.Citation48

Face-validity was established in only two studies.Citation1,Citation8 In the first study, the TFI was checked by participants at geriatric meetings and in the second study, conducted in Denmark, after translating the TFI, a pretest was performed by cognitive interviewing concluding that the TFI could be further tested in practice.

Structural Validity and Known-Groups Validity

Both structural validity and known-groups validity were only determined by Vrotsou et al (see ).Citation14 Fit indexes of a second-order model of three factors (frailty domains) were acceptable and the TFI differentiated well between frail and non-frail people, as defined by the Gérontopôle Frailty Screening Tool (GFST)Citation56 and the Short Physical Performance Battery (SPPB).Citation57

Discussion

The TFI is a questionnaire that is increasingly used to determine frailty in older people. Since the introduction of the TFI in 2010, many studies on its psychometric properties have been conducted. In this study, we aimed to present a review of findings regarding the reliability and validity of the TFI. The present study is the first to assess these psychometric properties of the TFI.

The literature search performed through May 30, 2020, showed that 27 studies reported on the psychometric properties of the TFI, as related to reliability, validity or both. Most of the studies (n = 25) were focused on community-dwelling older people. Since the TFI was developed in the Netherlands,Citation1 it is not surprising that 13 of the included studies were conducted in that country and there appeared to be large differences in the prevalence of frailty. The lowest and highest prevalence figures were 12.4%Citation13 and 76.5%,Citation39 respectively. Our review shows higher prevalence figures of frailty are closely related to greater age. This finding is supported by a systematic review containing cross‐sectional data from community‐based cohorts.Citation58 In addition, we found higher prevalence figures among people residing in settings other than the community, eg, acutely admitted patients,Citation49 residents of assisted living facilities,Citation39 and people admitted to a geriatrics outpatient clinic.Citation15 Zhang et al emphasized that the mean score on the TFI is influenced by the country of residence of the participants.Citation47 For example, the mean score for people with an average age of 75.3 years from Greece was 5.80, while this score was 4.25 in a sample of Dutch people with an average age of 81.5 years.Citation47 The country of residence of the participants may also be the possible explanation for the high prevalence among older Portuguese people (54.8%);Citation10 this prevalence is exceptionally high if we consider that the TFI cut-off point of 6Citation10 was taken, not the established cut-off point of 5.Citation1

Our study shows that the reliability of the TFI has been comprehensively assessed; 15 and nine studies examined the internal consistency and test–retest reliability, respectively. In many cases, the reliability of the TFI, reflected by Cronbach’s alpha, was >0.70, which indicates satisfactory reliability.Citation24 The internal consistency of the individual domains of the TFI was worse, particularly for the psychological and social domains, which can be explained by the fact that these domains only contain four and three items. Test–retest reliability, reflected by correlations (>0.60) and ICC (>0.75), was good.Citation25,Citation27 Moreover, kappa coefficients showed a substantial or nearly perfect level of agreement concerning many individual TFI items. The two other types of reliability, inter-rater and parallel forms, have only been examined to a limited extent.Citation13,Citation15,Citation46

The validity of the TFI has been established in 24 studies. In many studies focusing on criterion validity (concurrent and predictive), adverse outcomes of interest were disability, increased health-care utilization, lower quality of life and mortality. Regarding disability, studies predominantly show results that are excellent,Citation1,Citation9,Citation38,Citation42,Citation47 with AUCs >0.80.Citation29 The findings pertaining to an increase in health-care utilization present a less unambiguous picture and seem to depend strongly on the indicator used (eg, personal care, informal care, visits to a general practitioner or hospitalization). The TFI, however, clearly has a poor association with visits to a general practitionerCitation1,Citation9,Citation42 and hospitalization.Citation1,Citation13,Citation37Citation39,Citation42,Citation43 In all six studies using quality of life as the outcome, the TFI showed good associations with lower quality of life, independent of the quality of life instrument that has been used.Citation1,Citation10,Citation40Citation42,Citation45 Moreover, the TFI predicted mortality, with only Op Het Veld et alCitation43 qualifying the predicted value for this outcome as low. It should be noted that follow-up periods were short, consisting of 1 or 2 years, except the study by Theou et alCitation46 that included a follow-up of 5 years. Unfortunately, Theou et al did not use the original TFI for assessing frailty.Citation46 Therefore, we recommend determining the prediction value of the original TFI for mortality using a follow-up period >5 years. Finally, concerning criterion validity, the TFI showed discriminating ability in regards to GFI,Citation10 SHARE-FI,Citation47 and FI,Citation13 reflected by excellent AUCs (>0.80).

Construct validity of the TFI, distinguishing convergent and divergent validity, was established in nine studies. In many cases, the domains and components of the TFI correlated as expected with alternative measures providing evidence for good construct validity. Content and face validity were only determined in threeCitation1,Citation46,Citation48 and two studies,Citation1,Citation8 respectively. Two of these studies were qualitative in nature,Citation8,Citation48 which seems ideally suited to establish these types of validity. In our opinion, to validating an instrument like the TFI, the involvement of preferably older people, is necessary, whom, from their perspective, can indicate what needs to be questioned in the context of frailty. Only one study assessed the structural and known groups validity.Citation14 These findings were satisfactory.

Some limitations of our study should be noted. First, different instruments and questions have been used to assess disability, eg, Groningen Activity Restriction Scale (GARS)Citation59 and Katz scale,Citation60 and indicators of health-care utilization. Differences concerning variables controlled in regression analyses also exist, which could have influenced the findings. Secondly, many of the included studies aimed to determine the reliability and validity of the TFI were conducted in samples of community-dwelling older people. More studies are needed in order to establish good reliability and validity of the TFI in other samples of older people (eg, residents of assisted living facilities, nursing homes, mental health institutions and hospitalized patients). Thirdly, many data on reliability and validity were available and it was impossible to present all these data. A selection based on the most relevant data for the present study was therefore utilized and the individual studies were referred to for more detailed information. Finally, the majority of studies have been performed in Europe and especially in the Netherlands, with less in Brazil,Citation7,Citation51 Saudi Arabia,Citation52 and China.Citation13 The determination of the psychometric properties of the TFI in the other continents of the world, such as Africa, North America and Australia, is recommended.

The TFI is specifically designed for screening of multidimensional frailty among community-dwelling older people; our review provided much evidence that the TFI is ideally suited to that target group. Well-known determinants of frailty, assessed with the TFI, are higher age, being a woman, and a low socio-economic status, expressed by low-educational and low-income level.Citation36,Citation61,Citation62 To prevent frailty, it is recommended to start screening among people that meet those criteria. Based on this screening, primary health-care professionals (eg, general practitioners, nurses, physiotherapists, occupational therapists) can determine, preferably in a multidisciplinary consultation, whether these people need a comprehensive geriatric assessment (CGA) and a care needs assessment. In addition, the findings of the screening of frailty using the TFI can provide primary health-care professionals a first direction to the interventions that should be conducted next. Evidence of beneficial effects of multidomain interventions compared to unidomain interventions on frailty status or score is limited but increasing.Citation63

In conclusion, our literature search revealed 27 studies examining the reliability and/or validity of the TFI. Many studies showed that the internal consistency and test–retest reliability are noteworthy, as well as the criterion and construct validities. In contrast, the association of the TFI with some indicators of health-care utilization can be indicated as poor (eg, visits to a general practitioner or hospitalization). Knowing that population aging is occurring all over the world, the availability of the TFI is critical. In addition to the qualification of its psychometric properties as good, it is well known that the TFI is a user-friendly instrument for assessing frailty. The findings of this assessment can support health-care professionals in selecting interventions to reduce frailty and delay its adverse outcomes, such as disability and lower quality of life.

Disclosure

The authors report no conflicts of interest in this work.

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