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Study Design. Test-retest design. Objective. The objective was to examine the intrarater (test- retest) reliability of the core stability related tests and to develop.
SPINE Volume 41, Number 14, pp E844–E850 ß 2016 Wolters Kluwer Health, Inc. All rights reserved

CLINICAL CASE SERIES

Developing a Reliable Core Stability Assessment Battery for Patients With Nonspecific Low Back Pain Buse Ozcan Kahraman, MSc, PT, Yesim Salik Sengul, PhD, PT, Turhan Kahraman, MSc, PT, and Orhan Kalemci, MD y

Study Design. Test-retest design. Objective. The objective was to examine the intrarater (testretest) reliability of the core stability related tests and to develop a reliable core stability assessment battery. Summary of Background Data. Studies suggest that core stability exercises may improve function and decrease pain in patients with nonspecific low back pain (LBP). Reliable clinical tests are required to implement adequate rehabilitation and to evaluate results of these interventions. Methods. The study had a test-retest design. Thirty-three different tests that might relate to core stability were identified with their mostly used protocols. Five different components of core stability including endurance, flexibility, strength, functional performance, and motor control were assessed in 38 patients with nonspecific LBP. The same testing procedure was performed again after 48 to 72 hours. Intraclass correlation coefficients (ICCs), standard error of measurement, and minimal detectable change were calculated to assess the intrarater reliability. Results. The intrarater reliability of the tests ranged from little to very high (ICC ¼ 0.08–0.98). Partial curl-up (ICC ¼ 0.90), lateral bridge (ICC ¼ 0.95 – 0.96), trunk flexor endurance (ICC ¼ 0.97), sit and reach (ICC ¼ 0.98), single-legged hop (ICC ¼ 0.98–0.97), lateral step-down (ICC ¼ 0.93–0.92), eyes open right and left leg unilateral stance (ICC ¼ 0.97 and 0.91)

From the Dokuz Eylu¨l University, School of Physical Therapy and Rehabilitation, Izmir, Turkey; and yDokuz Eylu¨l University, Faculty of Medicine, Department of Neurosurgery, Izmir, Turkey. Acknowledgment date: September 24, 2015. Acceptance date: December 7, 2015. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No relevant financial activities outside the submitted work. Address correspondence and reprint requests to Yesim Salik Sengul, PhD, PT, Dokuz Eylu¨l University, School of Physical Therapy and Rehabilitation, Izmir, Turkey, TR 35340; E-mail: [email protected] DOI: 10.1097/BRS.0000000000001403

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tests had the highest intrarater reliability for each core stability component. Conclusion. The results indicated that the partial curl-up test (strength), side bridge and trunk flexor tests (endurance), sit-andreach test (flexibility), single-legged hop, and lateral step-down (functional), unilateral stance test with eyes open (motor control) had very high intrarater reliability. A core stability assessment battery involving these tests can be used in patients with nonspecific LBP to assess all components of core stability. Key words: activities of daily living, core stability, flexibility, functional performance, low back pain, motor activity, muscle strength, outcome measures, physical endurance, reliability. Level of Evidence: 3 Spine 2016;41:E844–E850

N

onspecific low back pain (LBP) is defined as LBP not attributable to a recognizable, known specific pathology and has become a major public health problem worldwide.1 As LBP often recurs and transforms into a chronic pain, it affects the individual’s quality of life and working life.2 Although core stability is used more frequently for improving physical fitness and athletic performance, current benefits and advantages of good core stability have been defined in the treatment of LBP3,4 and these exercises are one of the most used methods in patients with LBP.5 Because core muscles work synergistically in a way that they perform complex movements, core stability assessment with a single test is very difficult.6,7 Although there is no consensus on the definition and measurement of core stability, several tests and measurements are available that claim to measure and assess components of core stability. Core stability components include strength, endurance, flexibility, motor control, and function.8 Waldhelm and Li8 investigated intrarater reliability of 35 different measurements that assess these components in a sample of 15 healthy college-aged males. The results of this study, which included small sample size and healthy males, suggested that endurance tests were the most reliable core stability related

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July 2016

CLINICAL CASE SERIES measurements. The results suggested that endurance tests were the most reliable core stability related measurements. However, that study had a relative small sample and only included healthy males. The outcome of core stability exercises in patients with LBP is very important for both research and daily clinical practice. The reliability of the core stability measurement methods still needs to be examined in patients with nonspecific LBP. The assessment of treatment outcome is very important for both research and daily clinical practice. After a thorough review of the literature about the core stability and LBP, 33 different tests that may relate to core stability were identified and classified in five categories which are suggested for core stability components. The aim was to examine the intrarater (test-retest) reliability of the 33 different core stability related tests and to develop a reliable core stability assessment battery for patients with nonspecific LBP through selecting the tests that had the highest reliability. In reporting the results of the present study, guidelines for reporting reliability and agreement studies were followed.9

METHODS Study Design Test-retest design was used to examine the reliability. The demographic and clinical data of the patients were recorded. The patients reported the intensity of LBP in rest and activity with a 10-cm long line visual analog scale. We used the Oswestry Disability Index to determine disability levels of the patients.10,11 Five-minute walk with a moderate intensity was applied for warm-up before each testing session. A practice trial was performed for each test to allow the patient to become familiar with the protocol. The tests were performed in random order between and within the testing categories, except for the endurance tests. The endurance tests were performed in a within category random order last due to the fatiguing nature of the tests. Adequate resting periods were allowed between the tests. The second testing session was performed by the same physiotherapist in the same laboratory after 48 to 72 hours.

Participants The patients were recruited from March to July 2014. We included patients aged 18 to 55 years old with nonspecific LBP diagnosed by a neurosurgeon; chronic (more than 3 months) LBP; without secondary disorders (e.g. systemic illness, neurological or muscular degenerative disorders) that may preclude exercises. The exclusion criteria included the following: pregnancy; osteoporosis; physiotherapy received in the last 6 months; use of analgesics during the study period; not coming to the second testing session. The required sample size was determined using NCSS PASS 13. In one study, the sit-and-reach test had the highest intrarater reliability with a mean value of 4.20  2.77 cm.8 Based on this result, the sample size was calculated as 27 patients with a ¼ 0.05 (two-way) and power ¼ 0.80. The Spine

Reliable Core Stability Assessment Battery  Kahraman et al

data of 38 patients were eventually included in the statistical analyses while 12 patients who were not willing to participate and seven patients who did not come to the second testing session were excluded. The rater physiotherapist had 4-year clinical expertise and participated in several core stability courses. Another physiotherapist helped the rater physiotherapist and recorded the test results. Both physiotherapists were blinded to the results of the testing sessions. All procedures followed were in accordance with the ethical standards of the ethics committee of Dokuz Eylu¨l University with the Helsinki Declaration (Reference number: 1437-GOA). Informed consent was obtained from all patients for being included in the study.

Core Stability Measurements Strength Tests Maximal isometric trunk strength was tested by Manual Muscle Tester (Lafayette, Indiana, USA) which is a handheld dynamometer. The objective was that the physiotherapist overcomes or breaks the patient’s resistance. The modified protocols described in the previous studies were performed.12,13 The patients held each contraction for 5 seconds. The average of three measurements was recorded. The isoinertial strength tests were determined as the situp test, partial curl-up, and single-leg squat.14 The objective of the sit-up and partial curl-up tests was to perform as many full sit-ups and curl-ups as possible within 1 minute.8,15 A modified protocol was used to perform the single-leg squats.16 The starting position for the single-leg squat was standing on the test leg with the hip and knee in a neutral anatomical position. The trunk was upright and the contralateral leg was positioned with the hip in neutral and the knee in approximately 908 of flexion. The patients moved as fast as possible into a squat position, when the test knee reached 608 of flexion, and then returned to the starting position. The test was done for 30 seconds for each lower extremity. Endurance Tests Four core endurance tests were performed with the following protocols described by McGill et al.17 The objective of the tests was to hold a static position for as long as possible. The endurance tests were the trunk flexor, Sorenson (trunk extensor), and bilateral side bridge tests. The side bridge tests were stopped when the side-lying position was lost or when the hips touched to the table. The trunk flexor and Sorenson tests were stopped when the patient disrupted the position. Flexibility Tests Flexibility tests included active range of motion measurements for the trunk and sit-and-reach test. The protocols for trunk flexion, extension, and rotation were based on Norkin and White.18 The distance between spinous processes of C7 and S1 vertebras was measured while standing in full flexion www.spinejournal.com

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CLINICAL CASE SERIES and extension. The trunk rotation was measured with a 30cm goniometer with the patient sitting in a chair. Patients rotated their trunk and head as far as possible in both directions. The sit-and-reach test was performed with a sit-and-reach box with the protocol described by Jackson et al.19 The patient completed three reaches and the best reach was recorded. Functional Tests The single-legged hop test for distance was performed with the patient standing on the leg to be tested, hopping as far as possible, and landing on the same leg.20 The patients performed three hops and the best hop distance was recorded for each lower extremity. The protocol for the lateral step-down was adopted from the previous studies.21,22 The patients stood on the test leg, which was positioned on the edge of a step (20 cm), with the hip and knee in a neutral anatomical position. The trunk was upright, the level was at the iliac crests, and the contralateral leg was unsupported, with the hip in a slightly flexed position and the knee extended. The patients lowered themselves as fast as possible until the contralateral heel contacted the ground and then returned to the starting position. The number of repetitions that the patient performed in 30 seconds was recorded. Motor Control Tests Balance Master System (NeuroCom International, Inc., Clackamas, Oregon, USA), which provides objective assessment of sensory and voluntary balance control, was used to measure the motor control. The system provides quantitative assessments of static and dynamic balance performance. The standard protocols described in Balance Master System Operator’s Manual were used.23 All the tasks were performed for three times. The modified clinical test of sensory interaction on balance (mCTSIB), unilateral stance test (UST), and limits of stability (LOS) were performed.

Statistical Analysis The data were analyzed using the IBM SPSS Statistics (Version 20.0). A two-way random model of intraclass correlation coefficient (ICC) was used to estimate relative intrarater reliability.24 ICC (2,1) was used since it included the variability of measurements for any session on any patient. A 95% confidence interval (CI) was reported to indicate the precision of the estimates. The degree of reliability was reported as little: 0.00 to 0.25, low: 0.26 to 0.49, moderate: 0.50 to 0.69, high: 0.70 to 0.89, and very high: 0.90 to 1.00.25 To assess absolute reliability, standard error of measurement (SEM) was calculated as the square root of the mean square error term derived from analysis of variance.21 To estimate the change between the testing sessions that might be clinically significant, minimal detectable change (MDC), was defined as 95% CI of SEM. MDC was calculated according to the following formula: MDC ¼ SEM  1.96  H2. In addition, coefficient of variation (CV) was determined for comparison of absolute reliability between different tests E846

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Reliable Core Stability Assessment Battery  Kahraman et al

(CV ¼ SD/mean  100).26 This was achieved by calculating mean CV from individual CVs.27

RESULTS There were 14 females (37%) and 24 males (63%) with a mean age of 35  10 years and mean body mass index of 25.34  4.11 kg/m2. The patients had suffered from pain for a mean period of 7  3 months and had moderate disability (mean Oswestry Disability Index ¼ 22%). A testing session took about an hour. The means of LBP intensity were 21.31  15.09 mm in resting and 64.47  20.09 mm at activity in the beginning of first testing session. The means of the second session were 22.36  11.15 mm (resting) and 64.47  20.49 mm (activity). There was no significant difference between the first and second sessions in terms of both resting and activity pain intensity (P > 0.05). Table 1 presents descriptive results of mean  SD of all core stability tests for the first and second testing sessions. Table 2 presents the intrarater reliability results. The strength tests had moderate to very high reliability (0.65– 0.90) with partial curl-up test having the highest (0.90). The endurance tests had high to very high reliability (0.88–0.97) with trunk flexor test having the highest (0.97). The flexibility tests had high to very high reliability (0.77–0.98) with sit-and-reach test having the highest (0.98). All functional tests had very high reliability (0.92–0.98). The motor control tests had little to very high reliability (0.08–0.97) with UST on right foot with eyes open having the highest (0.97).

DISCUSSION The results of current study indicated that the partial curl-up test (strength), side bridge and trunk flexor tests (endurance), sit-and-reach test (flexibility), single-legged hop, and lateral step-down (functional), UST with eyes open (motor control) had very high intrarater reliability. A core stability assessment battery including these tests can be used in patients with nonspecific LBP to assess all components of core stability. Our study was the first one to investigate the intrarater reliability of the maximal isometric trunk strength tests and indicated that they did not have adequate reliability. The isoinertial strength tests showed high to very high reliability. The partial curl-up test had the highest reliability. The previous studies also reported high reliability for isoinertial strength tests. For example, the curl-up and sit-up tests showed very high reliability (ICC ¼ 0.92 and 0.93, respectively) in healthy individuals.28,29 Munich et al30 reported the single-leg squat had a high reliability (ICC ¼ 0.89) similar to our results. Isoinertial tests are believed to be superior to the isokinetic and isometric tests since they measure the similar movements used in daily life activities31 and they are easy to perform and more cost-effective. In addition, the curl-up test has a widespread acceptance as an important isoinertial testing for core stability.14 Therefore, the partial curl-up test seems the best to measure the strength of core stability in patients with nonspecific LBP.

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CLINICAL CASE SERIES

Reliable Core Stability Assessment Battery  Kahraman et al

TABLE 1. Descriptive Statistics for Core Stability Related Tests Strength tests Trunk flexion (kg)

First Session Mean  SD

Second Session Mean  SD

14.22  3.52

14.00  3.93

Trunk extension (kg)

16.56  5.17

16.40  3.94

Sit-up test

20.97  7.46

21.71  8.41

Partial curl-up test

23.66  11.58

24.81  10.54

Right single-leg squat test

18.16  6.46

20.21  6.06

Left single-leg squat test

17.71  6.65

19.89  5.62

Endurance tests Right side bridge (sec)

33.58  29.64

33.12  28.53

Left side bridge (sec)

32.64  28.52

33.46  27.00

Sorensen test (sec)

32.21  24.62

33.90  27.03

Trunk flexor test (sec)

31.71  37.17

31.03  33.74

8.82  14.33

7.86  15.02

12.18  4.35

12.18  3.63

Flexibility tests Sit-and-reach test (cm) Trunk flexion (cm) Trunk extension (cm)

5.53  1.82

5.60  2.21

Trunk right rotation (o)

44.92  16.08

42.68  14.49

Trunk left rotation (o)

48.42  14.53

46.13  12.27

Functional tests Right single-legged hop test (cm)

129.76  43.43

127.86  45.15

Left single-legged hop test (cm)

130.11  48.04

129.10  45.14

Right lateral step-down test

20.82  7.41

21.92  6.93

Left lateral step-down test

21.11  7.65

21.94  7.05

0.33  0.16

0.39  0.21

Motor control tests mCTSIB Standing with eyes open on a firm surface (o/sec) Standing with eyes closed on a firm surface (o/sec)

0.33  0.11

0.35  0.12

Standing with eyes open on a foam surface (o/sec)

0.59  0.14

0.59  0.14

Standing with eyes closed on a foam surface (o/sec)

0.60  1.60

0.93  0.26

Composite sway (o/sec)

0.56  0.12

0.64  0.40

UST Standing on left foot with eyes open (o/sec)

1.11  0.71

0.99  0.66

Standing on right foot with eyes open (o/sec)

1.14  1.30

1.10  1.19

Standing on left foot with eyes closed (o/sec)

2.72  1.15

2.34  1.05

Standing on right foot with eyes closed (o/sec)

2.69  1.19

2.49  1.38

0.78  0.25

0.69  0.21

LOS Reaction time (%) Movement velocity (%)

4.36  1.59

4.63  1.48

Endpoint excursion (%)

75.60  10.76

76.55  9.48

Maximum excursion (%)

89.89  8.82

91.52  8.07

Directional control (%)

73.21  8.69

75.65  8.66

SD indicates standard deviation; mCTSIB, modified clinical test of sensory interaction on balance; UST, unilateral stance test; LOS, limits of stability.

The endurance tests also showed very high reliability in healthy individuals.17 Dedering et al32 reported high reliability (ICC ¼ 0.85) like our result for the Sorenson test in patients with lumbar disc herniation. Evans et al33 also reported high reliability (ICC ¼ 0.82–0.85) for side bridge tests and very high reliability (ICC ¼ 0.95) for trunk flexion test. Another study indicated that the trunk flexor and extensor tests had very high reliability (0.90) in office workers with subacute nonspecific LBP.34 The endurance tests are used widely in patients with LBP and our results are very similar compared to the earlier reports. Although all endurance tests showed adequate reliability in our study, we did not include the Sorenson test in the battery because it not only had lower reliability but also was less tolerable for the patients. Spine

The present study indicated that the sit-and-reach test had very high reliability. The previous studies also reported very high reliability (ICC ¼ 0.94–0.98) for the sit-and-reach test.35,36 We found that the trunk flexibility tests had a high reliability consistently with the results of other studies that were conducted in healthy people.8,36 The single-legged hop test had high to very high reliability results in patients after the anterior cruciate ligament repair surgery and in the professional athletes.37,38 Despite high reliability, the single-legged hop test has some disadvantage for patients with nonspecific LBP. It was observed that patients felt insecure during the test and increasing LBP severity at the contact with the ground. Also, it was confirmed by the patients while talking uncomfortable experience. However, the lateral www.spinejournal.com

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Reliable Core Stability Assessment Battery  Kahraman et al

TABLE 2. Intrarater Reliability Results for Core Stability Related Tests Strength tests Trunk flexion

ICC (2,1)

95% CI

SEM

MDC

CV

0.74y

0.56–0.86

1.88

5.21

26.41

Trunk extension

0.65z

0.42–0.80

2.71

7.51

27.62

Sit-up test

0.83y

0.71–0.91

3.20

8.87

37.16

Partial curl-up test

0.90

0.82–0.95

3.40

9.42

45.71

Right single-leg squat test

0.87y

0.77–0.93

2.22

6.15

32.78

Left single-leg squat test

0.87y

0.77–0.93

2.17

6.01

32.90

Endurance tests Right side bridge

0.95

0.91–0.97

6.37

17.66

87.20

Left side bridge

0.96

0.92–0.98

5.42

15.02

84.04

Sorensen test

0.88y

0.79–0.93

8.71

24.14

78.09

Trunk flexor test

0.97

0.94–0.98

5.96

16.52

112.98

Flexibility tests Sit-and-reach test

0.98

0.96–0.99

1.93

5.35

176.78

Trunk flexion

0.86y

0.75–0.92

1.47

4.07

32.76

Trunk extension

0.77y

0.60–0.87

0.96

2.66

36.19

Trunk right rotation

0.85y

0.73–0.92

5.90

16.35

34.87

Trunk left rotation

0.86y

0.76–0.92

4.88

13.53

28.30

Functional tests Right single-legged hop test

0.98

0.96–0.99

5.97

16.55

34.39

Left single-legged hop test

0.97

0.94–0.98

7.93

21.98

35.94

Right lateral step-down test

0.93

0.87–0.96

1.87

5.18

33.60

Left lateral step-down test

0.92

0.86–0.96

2.00

5.54

34.19

0.23{

0.9–0.51

0.17

0.47

51.17

Standing with eyes closed on a firm surface

0.52z

0.24–0.72

0.08

0.22

33.81

Standing with eyes open on a foam surface

0.19{

0.12–0.48

0.13

0.36

23.73

Standing with eyes closed on a foam surface

0.64z

0.40–0.79

0.15

0.42

147.31

Composite sway

0.08{

0.24–0.38

0.29

0.80

41.96

0.91

0.83–0.95

0.21

0.58

65.32

Standing on right foot with eyes open

0.97

0.95–0.98

0.18

0.50

111.11

Standing on left foot with eyes closed

0.53z

0.25–0.72

0.76

2.11

43.58

Standing on right foot with eyes closed

0.79y

0.63–0.88

0.59

1.64

49.83

Motor control tests mCTSIB Standing with eyes open on a firm surface

UST Standing on left foot with eyes open

LOS Reaction time

0.37§

0.07–0.62

0.19

0.53

31.24

Movement velocity

0.78y

0.62–0.88

0.71

1.97

34.22

Endpoint excursion

0.63z

0.40–0.79

6.12

16.96

13.31

Maximum excursion

0.84y

0.72–0.91

3.30

9.15

9.31

Directional control

0.62z

0.38–0.78

5.32

14.75

11.66



Very high reliability (0.90–1.00). high reliability (0.70–0.89). z moderate reliability (0.50–0.69). { little reliability (0.00–0.25) § low reliability (0.26–0.49). CI indicates confidence interval; CV, coefficient of variation; ICC, intraclass correlation coefficient; LOS, limits of stability; mCTSIB, modified clinical test of sensory interaction on balance; MDC, minimal detectable change; SEM, standard error of measurement; UST, unilateral stance test. y

step-down can be performed without these concerns. The lateral step-down test had controversial reliability results in the previous studies which found low to moderate reliability (ICC ¼ 0.39–0.67).21,39,40 However, they used different protocols. Although the number of repetitions was recorded in the present study, the others evaluated the quality of the single-leg movement subjectively during the task using a video-recording system. We preferred to use our protocol E848

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since it didn’t require a video-recording system and was similar to the protocols of other tests used in our study. Although we did not aim to compare these two lateral step-down protocols, our protocol seems to be better for the patients with nonspecific LBP since it had very high reliability. Both single-legged hop and lateral step-down had very high reliability. However, one should keep in mind the disadvantages of single-legged hop test.

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CLINICAL CASE SERIES The results of motor control tests were inconsistent with a wide range of ICCs. Waldhelm and Li8 observed higher reliability for UST with eyes closed (ICC ¼ 0.80–0.90) while our results showed moderate to high reliability. The LOS had moderate to high reliability (ICC ¼ 0.69–0.88) for healthy college students.41 Suttanon et al42 investigated the motor control tests in patients with Alzheimer disease and reported very high reliability (ICC ¼ 0.91) for mCTSIB while reporting low to high reliability for LOS (ICC ¼ 0.48– 0.71). As shown in the literature, motor control tests for different populations have very controversial results like ours. The controversial results may arise from different devices used in these studies or from the fact that motor control test devices are so sensitive that they cause getting more valuable information but also cause lower reliability. Taking everything into account, the motor control tests should be used with very caution in nonspecific LBP. The scores obtained on tests must have significant meanings to be useful in clinical and research practice. We reported the SEMs to identify the error associated with a patient’s test score, the MDCs to provide a threshold for interpreting the scores in the tests over time, and the CVs to compare of absolute reliability of the tests. These values are important in investigating the impact of interventions on patients with nonspecific LBP. Researchers and clinicians are referred to Table 2 to get more information about the SEMs and MDCs for each test. Our study had several limitations. Mostly female patients were not willing to participate in the study and the patients who did not come to the second testing session were mostly female. Most of the females were concerned about the number of the tests. We only investigated the intrarater reliability. The inter-rater reliability should also be investigated to provide more information about a test. However, adding an inter-rater reliability procedure would be very demanding for the patients. With our results, further studies can only focus on the tests having high intrarater reliability to examine their inter-rater reliability. Lastly, most of the tests can be performed with different protocols which can lead to different reliability results. The core stability tests used in the present study had adequate intrarater reliability except the motor control tests. A core stability assessment battery including the partial curlup test, side bridge and trunk flexor endurance tests, sit-andreach test, single-legged hop, and step-down, UTS with eyes open can be used in patients with nonspecific LBP to assess all components of core stability.

Key Points A reliable core stability assessment battery for patients with nonspecific LBP was developed in this study. This battery can assess the core stability in terms of strength, endurance, flexibility, functional, and motor control. Spine

Reliable Core Stability Assessment Battery  Kahraman et al

The partial curl-up test (strength), side bridge and trunk flexor tests (endurance), sit-and-reach test (flexibility), single-legged hop, and lateral stepdown (functional), UST with eyes open (motor control) were the tests that had the highest intrarater reliability.

Acknowledgment We would like to express our sincere thanks to Pembe Keskinoglu, Assoc Prof, MD from Dokuz Eylu¨l University, Department of Biostatistics and Medical Informatics for statistical help and advice.

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July 2016