Timed "Up & Go" Test as a predictor of falls within 6 months after hip fracture surgery.

Hip fracture after falls in elderly people represents an increasing challenge for the health care system worldwide. Approximately 30% of community-residing people aged 65 years or older fall each year, with higher numbers in institutions. (1) Hip fracture after falls has been related to preexisting mobility, balance, osteoporosis, and visual or other health problems. (2) Furthermore, Pearse et al (3) showed that 12% of patients with a hip fracture had a second hip fracture with a "significant further impact on patients' mobility and social independence." A prospective study by Stewart et al (4) involving a post-hip fracture follow-up at 52 weeks (25-80 weeks) for 394 patients who were more than 50 years of age revealed that a poor mobility score was a significant risk factor of a new fall. Prevention of falls, therefore, should be of the highest priority for all people with hip fracture during the stay at the orthopedic ward or rehabilitation unit and after discharge. In this context, methods for characterizing people at risk for falling are needed.

Scores on the Timed "Up & Go" Test (TUG), which measures functional mobility (in seconds), have been found in frail, community-dwelling older people to correlate well with scores on the Barthel Index of activities of daily living, on the Berg Balance Scale, and on gait speed testing (5); "the patients who took 30 seconds or more to complete the test, on the other hand, tended to need the assistance of others for many mobility tasks." (5) Very high intrarater and interrater reliability (5,6) and test-retest reliability (7) have been found for the TUG. Lusardi et al (8) found that age and the use of an assistive device were associated with significantly slower TUG scores (7.9-17.7 seconds) in community-dwelling people who were 66 to 101 years of age. Two studies of community-dwelling elderly people (9,10) revealed that a TUG score of more than 13 or 14 seconds was able to discriminate people who fell from people who did not fall in the preceding 6 months. Okumiya et al (11) found that a TUG score of more than 16 seconds predicted falls during a 5-year follow-up period. In contrast, Boulgarides et al (12) found that 5 balance tests, including the TUG, did not predict falls during a 12-month follow-up period for a group of 99 community-dwelling, older, active and independent adults who were 65 to 90 years of age.

The TUG has been used in several studies of people with hip fracture. Crotty et al (13) used the TUG as an outcome measure 12 months after home-based therapy for people with hip fracture and reported significant improvements in TUG scores. Similar results were reported by Mendelsohn et al (14) for people who had hip fracture and who were admitted to a specialized musculoskeletal inpatient rehabilitation program, by Kristensen et al (15) for a 6-month post-hip fracture follow-up period, and by Reardon et al (16) at 5 months after total hip arthroplasty. Hall et al (17) used the TUG to compare a group of community-dwelling subjects at 6 to 12 months after hip fracture with a matched community-dwelling group without fracture and found that the group with fracture was significantly slower (19 versus 10.5 seconds). In Denmark, the TUG with a cutoff point of 30 seconds was recommended as an indicator of the quality of treatment for people with hip fracture during their hospital stay. However, no prospective studies of the use of the TUG for predicting falls in people with hip fracture are available.

The aim of this prospective study, therefore, was to examine the use of the TUG performed at discharge with people with hip fracture who were discharged directly to their own residences or assisted-living facilities from an acute orthopedic hip fracture unit and with a cutoff point of 30 seconds as a potential predictor of falls during the 6-month postsurgery follow-up period. The risk of falls also was compared with age, prefracture residence, walking aids, type of fracture, mental status on admission, and the New Mobility Score (NMS), (18) which describes prefracture functional level.

Method

Subjects

Patients at the special orthopedic hip fracture unit at Hvidovre University Hospital between September 2002 and March 2003 were included prospectively as subjects in this study. The inclusion criterion was the ability of patients to perform the TUG at discharge directly to their own residences or to assisted-living facilities in the community. Patients primarily underwent rehabilitation directly in the orthopedic ward and were discharged when they were safely able to perform what Isaacs (19) has called the "basic mobility skills" of getting in and out of a bed and a chair, getting on and off of a toilet, and walking a few feet.

Patients who, after 2 to 3 weeks of initial rehabilitation at the orthopedic ward, still required inpatient rehabilitation were transferred to a secondary rehabilitation unit. During their hospital stay, all patients followed a well-defined care plan with multimodal fast-track rehabilitation (20,21); this plan included early surgery within 24 hours of admission, epidural anesthesia and epidural analgesia initiated immediately after admittance and continued for 96 hours after surgery, a standardized transfusion protocol if the hemoglobin level was less than 6.0 mmol/L, supplemental oxygen when the patient was positioned supine in the perisurgical period, prophylactic intraoperative antibiotics, perisurgical low-molecular-weight heparin, and enforced perisurgical oral nutrition and hydration, including energy and protein supplementation. The patients were mobilized on the day of surgery, and an intensive physical therapy program comprising 2 daily 30-minute sessions was initiated on the first day after surgery. After discharge, most patients continued physical therapy training twice weekly at hospital outpatient facilities until the final level of training was reached. All patients were contacted 6 months after surgery for a follow-up interview. All participants gave written informed consent.

A total of 79 subjects with hip fracture were included in this study. The median age of the subjects was 80 years; 15 subjects (19%) were younger than 65 years of age.

Measurements

Data were gathered prospectively, and a database was instituted for all patients admitted to the unit. This database comprised information on age; sex; body mass index; cerebrovascular, cardiovascular, and pulmonary diseases; diabetes; number of medications; type of fracture; and prefracture residential status, walking aids, and functional level evaluated with the NMS. (18) A validated 9-point Danish version of an abbreviated mental test was taken at admission. (22) The TUG was performed at discharge of patients from the unit to the community. Six months after the hip fracture surgery, all patients were contacted for a follow-up interview about falls since discharge from the hospital; all interviews were performed by one physical therapist with no knowledge of baseline data at the time of the interview.

The TUG measures the time (in seconds) that it takes an individual to rise from an armchair (chair seat height=45 cm), walk 3 m to a line drawn on the floor, and return to the chair. The time was measured from a seated position (back against the backrest) with a stopwatch started on the command "ready--go" and stopped when the seat position was reached again. The participant was given a practice trial followed by 1 timed trial performed on the day before discharge. All tests were conducted by 1 of 3 physical therapists after participation in a training session in accordance with national guidelines previously developed and examined for reliability in the study unit, with intratester and intertester reliability (Spearman correlation coefficient) of .91.

The NMS is a composite score of an individual's ability to perform indoor walking, outdoor walking, and shopping before the hip fracture and provides a score of between 0 and 3 for each function; the total score can range from 0 to 9, with 9 indicating a high prefracture functional level. The score was previously described as a predictor of long-term mortality (18) and rehabilitation, (15,18) with a cutoff point of 5. The mental score has a cutoff value of 5 or less for cognitive impairment, which has been described as an independent predictor of long-term mortality. (18)

The use of walking aids, which correlates with slower performance on the TUG, (10,23) also was assessed, with reports of the walking aid used during the TUG. We included patients who were younger than 65 years of age as subjects in this study because they comprise 12.5% of patients with hip fractures admitted to our unit and, as their fractures were due to a fall, they have the potential to fall again after discharge. All subjects were asked about the number of any unexpected falls from a standing position to the ground or floor since discharge.

Data Analysis

All data from subjects who were able to participate in the 6-month follow-up interview were compared with those from nonparticipants, and the potential for selected variables to predict falls at 6 months after the fracture was tested. The cutoff points for the individual variables were as follows:

** age--<80 or [greater than or equal to] 80 years

** prefracture residence--own homes or assisted living facilities

** walking aids--none, cane, 1- or 2- elbow crutches, or walker on wheels

** NMS score--0 to 5 (low) or 6 to 9 (high)

** dementia on admission--0 to 5 (dementia) or 6 to 9 (no dementia)

** type of fracture--cervical, trochanteric, or subtrochanteric

** TUG score--<30 or [greater than or equal to]30 seconds

** walking aids at discharge--1- or 2- elbow crutches, walker, or walker on wheels

Falls were classified as none or as 1 or more. Statistical analysis was conducted with SPSS for Windows version 10.1. * The level of significance was set at P<.05. Significant differences between groups were investigated with the chi-square test for categorical data and with the Fisher exact test for continuous numerical data.

Results

The TUG was performed at a median of 10 days (range=3-40) after surgery. At 6 months, 59 of the 79 subjects (75%; 8 of whom were younger than 65 years of age) were able to participate in the follow-up interview. The prefracture characteristics and postsurgery data for the subjects are shown in Table 1, and the exclusion criteria for the 20 subjects who were not able to participate in the 6-month follow-up interview are shown in Figure 1. Among the 59 subjects in the follow-up group, 19 subjects (32%) experienced from 1 to 4 falls (median= 2) in the period since discharge; 4 of these falls resulted in new hip fractures, and 18 of the subjects who fell scored more than 24 seconds on the TUG. Eighty-five percent of the subjects in the follow-up group received a plan for additional physical therapy after discharge.

[FIGURE 1 OMITTED]

The analyses of all predictors were examined, and the categorical outcome of 1 or more falls versus no falls showed that only the TUG performed at discharge with a cutoff point of 30 seconds was significantly (P=.02) associated with falls (Tab. 2). All subjects used walking aids when performing the TUG, and a progressive tendency toward falls was seen with the use of more assistive aids, because 15 (79%) of the subjects who fell used a walker or a walker on wheels rather than crutches. The TUG scores are shown in Figure 2; the median TUG scores were 42 seconds for subjects who fell and 29.5 seconds for subjects who did not fall. Only 3 subjects who fell had TUG scores of less than 30 seconds. In accordance with the directions given by Riddle and Stratford, (24) the sensitivity, specificity, predictive values, and likelihood ratios of the TUG are shown in Table 3; the TUG had very high sensitivity and negative predictive values for several cutoff points. A cutoff point of 24 seconds rather than 30 seconds strengthened the data (P=.01), resulting in a sensitivity of 95%, a negative predictive value of 93%, and a negative likelihood ratio of 0.1.

[FIGURE 2 OMITTED]

Discussion and Conclusion

The present study showed that the TUG performed at discharge with people with hip fracture who were discharged directly to their own homes or to assisted living facilities from an acute orthopedic hip fracture unit and with a cutoff point of 24 seconds was a valid predictor of falls in people with hip fracture within the first 6 months after discharge. Thus, 95% of subjects who fell had TUG scores of [greater than or equal to] 24 seconds; TUG scores of <24 seconds resulted in the prediction of 93% of subjects who did not fall, and these subjects were only 0.1 times as likely to fall as were other subjects.

Several studies previously assessed predictors of falls in elderly people, but most studies were conducted among community dwellers. Tinetti et al (25) studied 1,103 older people ([greater than or equal to] 72 years of age) living in the community for a median follow-up of 31 months and found that cognitive impairment, the presence of at least 2 chronic conditions, balance and gait impairments, and a low body mass index were independently associated with an individual experiencing a serious injury during a fall. Tinetti et al (26) also found that the risk of falling increased linearly with the number of risk factors, from 8% with none to 78% with 4 or more; these results suggested that measurements of balance and gait impairments should be combined with other risk factors, such as sedative use, cognitive impairment, disability of the lower extremities, palmomental reflexes, and foot problems. Similar results were found in a 12-month follow-up study (27) for 1,517 elderly subjects who were ambulatory; in that study, lower-limb muscle power and balance and gait functions were stronger predictors of falls and recurrent falls than other clinical predictors. Similarly, functional mobility evaluated with the TUG discriminated between subjects who fell and subjects who did not fall. (28)

Other studies (9,10) established cutoff points for the TUG of 13 and 14 seconds for discriminating retrospectively between subjects who fell and subjects who did not fall. The only previous study in which the TUG was found to predict falls was a Japanese study (11) with 278 older people (>75 years of age) who had not fallen before and who were followed over a 5-year period; in that study, a TUG score of >16 seconds was established as an independent predictor of falls, with a sensitivity of 54%, a specificity of 74%, and a positive predictive value of 44%. Our cutoff point of 24 seconds for predicting falls is higher than that in this last study. Our assessment was performed at a median of 10 days after surgery; in another study, (17) TUG scores after hip fracture were obtained at later times (6-12 months). Thus, different cutoff points for different patient populations at different times during rehabilitation may be necessary. Therefore, this prospective study using the TUG in the early period of rehabilitation and establishing cutoff points for people with hip fracture and at risk of new falls demonstrates that the TUG may be a valuable tool in future fall prevention efforts following hip fracture.

We are aware that our study design, which was reliant on the ability to recall falls during a 6-month period after hip fracture, could have led to some falls not being recalled, as indicated by Cummings et al. (29) A log system might have provided a more accurate registration of falls, but other studies (9,28) have used the same design as that used for our follow-up group.

One study (10) separating people with falls from people without falls included only older adults with 2 or more falls. Another study showed that "nonfallers were significantly faster than both one-time fallers and frequent fallers (P<.01) during the Get Up and Go." (28)(p M674) In our opinion, because a single fall may be fatal in this frail group, the cutoff in the present study was set at people without falls versus those with 1 or more falls.

However, our study also has some limitations in that only subjects who could perform the TUG at discharge were assessed; therefore, the subjects who were assessed were not those with the lowest functional ability. This limitation is inherent in the TUG, in that the ability to perform the test requires a moderate functional capacity. In addition, the number of subjects in our study was relatively small. Further studies with larger groups of subjects and measurements of functional mobility that can be used during their hospital stay and at discharge for all patients, regardless of functional level, are needed. A measure that evaluates daily walking ability for all patients during their hospital stay, such as the Cumulated Ambulation Score, (30) may be useful. In conclusion, our study showed that a TUG score of more than 24 seconds at discharge was a significant predictor for falls within 6 months after hip fracture.

Mr Kristensen provided writing. Dr Foss provided data analysis. Dr Kehlet provided consultation (including review of manuscript before submission).

This study was part of the Hvidovre University Hospital Hip Fracture Project, which was approved by the local ethics committee, and the study was approved by the Danish Data Protection Agency.

This work received financial support from IMK Fonden (Copenhagen, Denmark).

This research was presented as a platform presentation at the Danish Physiotherapy Congress; March 23-25, 2006; Odense, Denmark.

References

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(3) Pearse EO, Redfern DJ, Sinha M, Edge AJ. Outcome following a second hip fracture. Injury. 2003;34:518-521.

(4) Stewart A, Walker LG, Porter RW, et al. Predicting a second hip fracture. J Clin Densitom. 1999;2:363-370.

(5) Podsiadlo D, Richardson S. The Timed "Up & Go": a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc. 1991;39:142-148.

(6) Lin M-R, Hwang H-F, Hu M-H, et al. Psychometric comparisons of the timed up and go, one-leg stand, functional reach, and Tinetti balance measures In community-dwelling older people. J Am Geriatr Soc. 2004;52:1343-1348.

(7) Steffen TM, Hacker TA, Mollinger L. Age-and gender-related test performance in community-dwelling elderly people: Six-Minute Walk Test, Berg Balance Scale, Timed "Up & Go" Test, and gait speeds. Phys Ther. 2002;82:128-137.

(8) Lusardi MM, Pellecchia GL, Schulman M. Functional performance in community living older adults. J Geriatr Phys Ther. 2003;3:14-22.

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(10) Shumway-Cook A, Brauer S, Woollacott M. Predicting the probability for falls in community-dwelling older adults using the Timed "Up & Go" Test. Phys Ther. 2000; 80:896-903.

(11) Okumiya K, Matsubayashi K, Nakamura T, et al. The Timed "Up & Go" test is a useful predictor of falls in community-dwelling older people. J Am Geriatr Soc. 1998;46: 928-930.

(12) Boulgarides LK, McGinty SM, Willet JA, Barnes CW. Use of clinical and impairment-based tests to predict falls by community-dwelling older adults. Phys Ther. 2003;83:328-339.

(13) Crotty M, Whitehead C, Miller M, Gray S. Patient and caregiver outcomes 12 months after home-based therapy for hip fracture: a randomized controlled trial. Arch Phys Med Rehabil. 2003;84: 1237-1239.

(14) Mendelsohn ME, Leidl DS, Overend TJ, Petrella RJ. Specificity of functional mobility measures in older adults after hip fracture: a pilot study. Am J Phys Med Rehabil. 2003;82:766-774.

(15) Kristensen MT, Foss NB, Kehlet H. Timed Up & Go and New Mobility Score as predictors of function six months after hip fracture [in Danish]. Ugeskr Laeger. 2005; 167:3297-3300.

(16) Reardon K, Galea M, Dennett X, et al. Quadriceps muscle wasting persists 5 months after total hip arthroplasty for osteoarthritis of the hip: a pilot study. Int Med J. 2001;31:7-14.

(17) Hall SE, Williams JA, Senior JA, et al. Hip fracture outcomes: quality of life and functional status in older adults living in the community. Aust N Z J Med. 2000;30: 327-332.

(18) Parker MJ, Palmer CR. A new mobility score for predicting mortality after hip fracture. J Bone Joint Surg Br. 1993;75: 797-798.

(19) Isaacs B. Clinical and laboratory studies of falls in old people: prospects for prevention. Clin Geriatr Med. 1985;1:513-524.

(20) Foss NB, Kristensen MT, Jensen PS, et al. Effect of postoperative epidural analgesia on rehabilitation and pain after hip fracture surgery. Anesthesiology. 2005;102: 1197-1204.

(21) Foss NB, Kehlet H. Mortality analysis in hip fracture patients: implications for design of future outcome trials. Br J Anaesth. 2005;94:24-29.

(22) Quereshhi KN, Hodldnson HM. Evaluation of a ten-question mental test in the institutionalized elderly. Age Ageing. 1974;3: 152-157.

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(24) Riddle DL, Stratford PW. Interpreting validity indexes for diagnostic tests: an illustration using the Berg balance test. Phys Ther. 1999;79:939-948.

(25) Tinetti ME, Doucette J, Claus E, Marottoli R. Risk factors for serious injury during falls by older persons in the community. J Am Geriatr Soc. 1995;43:1214-1221.

(26) Tinetti ME, Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. N Engl J Med. 1988;319:1701-1707.

(27) Chu LW, Chi I, Chiu AYY. Incidence and predictors of falls in the Chinese elderly. Ann Acad Med Singapore. 2005;34: 60-72.

(28) Gunter KB, White KN, Hayes WC, et al. Functional mobility discriminates nonfallers from one-time and frequent fallers. J Gerontol A Biol Sci Med Sci. 2000;55: M672-M676.

(29) Cummings SR, Nevitt MC, Kidd S. Forgetting falls: the limited accuracy of recall of falls in the elderly. J Am Geriatr Soc. 1988;36:613-616.

(30) Foss NB, Kristensen MT, Kehlet H. Prediction of postoperative morbidity, mortality and rehabilitation in hip fracture patients: the cumulated ambulation score. Clin Rehabil. 2006;20:701-708.

* SPSS Inc, 233 Wacker Dr, Chicago, IL 60606.

MT Kristensen is Research Physiotherapist, Department of Physiotherapy, Hvidovre University Hospital, Copenhagen, Denmark. Address all correspondence to Mr Kristensen at: morten.tange. [e-mail].

NB Foss, MD, is Research Fellow, Department of Anaesthesiology and Orthopaedics, Hvidovre University Hospital.

H Kehlet, MD, PhD, is Professor, Section of Surgical Pathophysiology, The Juliane Marie Centre, Righospitalet, Copenhagen, Denmark.

[Kristensen MT, Foss NB, Kehlet H. Timed "Up & Go" Test as a predictor of falls within 6 months after hip fracture surgery. Phys Ther. 2007;87:24-30.]

[C] 2007 American Physical Therapy Association

This article was received August 25, 2005, and was accepted August 21, 2006.

Table 1.
Baseline Characteristics and Results for 79 Subjects Included in
a 6-Month Follow-up Study of the Use of the Timed "Up & Go" Test for
Predicting Falls After Hip Fracture (a)

Characteristic                  Subjects With       Subjects Without
                                Follow-up Data      Follow-up Data
                                (n=59)              (n=20)

Age (y)                         81 (42-97)          75 (47-89)
Women                           45 (76)             14 (70)
Body mass index                 23.8 (21.1-26.0)    21.5 (21.0-26.0)
Living in own residence         54 (92)             18 (90)
Prefracture walking aids        24 (41)              7 (35)
Low prefracture functional      13 (22)              5 (25)
  level (New Mobility
  Score of <6)
Cerebrovascular disease          8 (14)              2 (10)
Cardiovascular disease          35 (59)             12 (60)
Pulmonary disease               11 (19)              4 (20)
Diabetes                         2 (3)               1 (5)
No. of medications               2 (1-4)             2 (0-5)
Dementia on admission            3 (5)               2 (10)
Fracture type
  Cervical                      30 (51)             14 (70)
  Trochanteric                  26 (44)              4 (20)
  Subtrochanteric                3 (3)               2 (10)
Walking aids at discharge       59 (100)            18 (90)
Low functional mobility at      36 (61)             12 (60)
  discharge (Timed "Up & Go"
  Test score of [greater than
  or equal to] 30 s)
Postsurgical day of Timed "Up   10 (3-40)           11 (3-35)
  & Go" Test

(a) Data are presented as number (percentage) for categorical data
and as median (interval) for numerical data. There were no
significant differences between groups.

Table 2.
Associations Between All Predictors and the Categorical Outcome of
Falls Versus No Falls and Significance of Associations for 59 Subjects
Discharged Directly to Their Own Homes or Assisted Living Facilities
From an Acute Orthopedic Hip Fracture Unit (a)

Parameter                             Subjects         Subjects
                                      With Falls       Without Falls
                                      (n=19)           (n=40)

Age (<80 y/ [greater than              8 (42)/11       20 (50)/20
  or equal to] 80 y)

Living in own residences/             16 (84)/3        38 (95)/2
  assisted living facilities

Prefracture walking aids:             7/4/1/0/7        28/4/1/1/6
  none/cane/1- or 2- elbow
  crutches/walker on wheels

Prefracture functional level           6 (32)/13        7 (18)/33
  (New Mobility Score of 0-5/6-9)

Dementia on admission (yes/no)         1 (5)/18         2 (5)/38

Fracture type: cervical/              10 (53)/8/1      20 (50)/18/2
  trochanteric/ subtrochanteric

Walking aids at discharge: 1- or       0/4/6/9          4/15/11/10
  2-elbow crutches/ walker/walker
  on wheels

Functional mobility at discharge       3 (16)/16        18 (45)/22
  (Timed "Up & Go" Test score of
  <30 s/[greater than or equal
  to] 30 s)

Parameter                             P

Age (<80 y/ [greater than             .38 (b)
  or equal to] 80 y)

Living in own residences/             .32 (c)
  assisted living facilities

Prefracture walking aids:             .13 (b)
  none/cane/1- or 2- elbow
  crutches/walker on wheels

Prefracture functional level          .22 (b)
  (New Mobility Score of 0-5/6-9)

Dementia on admission (yes/no)        1.00 (c)

Fracture type: cervical/              .98 (b)
  trochanteric/ subtrochanteric

Walking aids at discharge: 1- or      .17 (b)
  2-elbow crutches/ walker/walker
  on wheels

Functional mobility at discharge      .02 (c)
  (Timed "Up & Go" Test score of
  <30 s/[greater than or equal
  to] 30 s)

(a) Data are presented as number (percentage).

(b) The chi-square test was used as the statistical test for
significance.

(c) The Fisher exact test was used as the statistical test
for significance.

Table 3.
Predictive Values and 95% Confidence Intervals (CI) for Several
Different Cutoff Points of the Timed "Up & Go" Test (TUG) for
Predicting Falls Within 6 Months After Discharge for 59 Subjects
Discharged Directly to Their Own Homes or Assisted Living
Facilities From an Acute Orthopedic Hip Fracture Unit (a)

TUG Score,                            Positive          Negative
in Seconds                            Predictive        Predictive
(No. of                               Value             Value
Subjects)                             (95% CI)          (95% CI)

[greater than or equal to] 20 (54)    33 (21-46)        80 (45-100)
[greater than or equal to] 24 (44)    41 (26-55)        93 (81-100)
[greater than or equal to] 30 (34)    47 (30-64)        88 (75-100)
[greater than or equal to] 34 (28)    50 (31-69)        84 (71-97)

TUG Score,                            Sensitivity       Specificity
in Seconds                            (95% CI)          (95% CI)
(No. of
Subjects)

[greater than or equal to] 20 (54)    95 (75-99)        10 (4-23)
[greater than or equal to] 24 (44)    95 (75-99)        35 (22-51)
[greater than or equal to] 30 (34)    84 (62-94)        55 (40-69)
[greater than or equal to] 34 (28)    74 (51-88)        65 (50-77)

TUG Score,                            Positive          Negative
in Seconds                            Likelihood        Likelihood,
(No. of                               Ratio             Ratio
Subjects)                             (95% CI)          (95% CI)

[greater than or equal to] 20 (54)    1.1 (0.9-1.2)     0.5 (0.1-4.4)
[greater than or equal to] 24 (44)    1.5 (1.1-1.8)     0.1 (0.0-1.1)
[greater than or equal to] 30 (34)    1.9 (1.3-2.8)     0.3 (0.1-0.8)
[greater than or equal to] 34 (28)    2.1 (1.3-3.4)     0.4 (0.2-0.9)

(a) Data are reported as percentages unless otherwise indicated.