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Table 1 Descriptive statistics and intra-practice correlation coefficients

From: Intra-cluster correlation coefficients in adults with diabetes in primary care practices: the Vermont Diabetes Information System field survey

Variable

N

No

Mean or percent

SD

SE

ICC

95% confidence interval

Demographic, social and economic characteristics

Sex (% male)

8808

119.7

48.4

 

1.3

0.038

0.021, 0.056

Age (years)

8286

117.3

63.1

13.9

0.5

0.077

0.045, 0.109

Married (%)

1004

14.5

62.5

 

1.6

0.009

0, 0.036

High School Graduate (%)

999

14.4

75.4

 

1.6

0.011

0, 0.038

Income <$30,000 per year (%)

931

13.4

59.0

 

2.1

0.042

0.003, 0.081

Private insurance (%)

1001

14.4

58.4

 

2.0

0.050

0.011, 0.090

Medicare (%)

997

14.4

59.9

 

1.7

0.018

0, 0.047

Medicaid (%)

995

14.3

21.4

 

1.8

0.036

0, 0.071

Military or veterans' insurance (%)

994

14.3

5.2

 

0.8

0.029

0, 0.062

No insurance (%)

993

14.3

2.4

 

0.6

0.035

0, 0.070

Travel distance from home to Primary Care provider (km)

2955

76.5

13.7

15.3

1.8

0.196

0.102, 0.289

Non-Hispanic white (%)

1004

14.5

97.3

 

0.5

0.003

0, 0.028

Physical characteristics

Heart Rate (beats per min)

998

14.4

75.0

13.0

0.5

0.015

0, 0.043

Systolic blood pressure (mmHg)

999

14.4

140.3

19.6

0.8

0.042

0.005, 0.079

Diastolic blood pressure (mmHg)

999

14.4

78.3

10.5

0.4

0.017

0, 0.047

Blood pressure below 130/80 mmHg (%)

999

14.4

25.0

 

1.6

0.028

0, 0.061

Blood pressure over 140/90 mmHg (%)

999

14.4

49.2

 

2.3

0.069

0.024, 0.114

Height (cm)

998

14.4

165.2

10.4

0.4

0.019

0, 0.048

Weight (kg)

997

14.4

203.0

47.7

1.6

0.011

0, 0.038

Body Mass Index (kg/m2)

994

14.3

33.8

7.4

0.2

0.011

0, 0.039

Body Mass Index >30 kg/m2 (%)

994

14.3

67.2

 

1.6

0.010

0, 0.038

Laboratory results

Mean glycosolated hemoglobin (A1C) (%)

8711

118.4

7.01

1.45

0.05

0.055

0.032, 0.079

A1C >8.0% (%)

8711

118.4

18.1

 

1.0

0.025

0.013, 0.037

A1C <7.0 (%)

8711

118.4

61.7

 

1.6

0.046

0.026, 0.066

Total cholesterol (mg/dl)

8167

112.5

184.4

41.8

1.2

0.037

0.020, 0.054

LDL-cholesterol (mg/dl)

7834

111.0

105.8

34.2

1.0

0.045

0.025, 0.065

LDL <100 mg/dl (%) *

7873

111.6

43.8

 

1.4

0.029

0.020, 0.055

Triglycerides (mg/dl)

7969

109.8

190.5

161.3

3.3

0.014

0.006, 0.022

Serum creatinine (mg/dl)

8474

115.1

1.12

0.70

0.02

0.080

0.048, 0.112

Urine microalbumin to creatinine ratio (mg/mmol)

3039

46.7

47.0

260.7

10.0

0.101

0.051, 0.152

Urine microalbumin to creatinine ratio <30 mg/mmol (%)

3338

49.0

67.3

 

1.5

0.031

0.011, 0.051

Quality of care (Process Measures)

Creatinine on time (%)

8808

119.7

79.4

 

3.1

0.288

0.203, 0.373

Urine microalbumin to creatinine ratio on time (%)

8808

119.7

24.6

 

2.3

0.162

0.105, 0.219

A1C on time (%)

8808

119.7

50.7

 

2.4

0.118

0.074, 0.162

Lipids on time (%)

8808

119.7

70.3

 

3.0

0.199

0.132, 0.265

A1C on time & <7% (%)

7308

113.2

35.5

 

1.5

0.040

0.021, 0.060

LDL on time & <100 mg/dl (%)

7308

113.2

31.3

 

1.4

0.040

0.021, 0.059

Influenza vaccine given (%)

995

14.3

80.5

 

1.4

0.058

0.016, 0.100

Pneumonia vaccine given (%)

913

13.2

70.6

 

1.8

0.058

0.014, 0.102

Health habits

Alcoholic drinks per week

988

14.2

1.6

4.5

0.2

0.027

0, 0.060

CAGE score (0–4)

946

13.6

0.2

0.7

0.2

0.009

0, 0.038

Tobacco smoker (%)

1006

14.5

16.9

 

1.2

0.005

0, 0.030

Cigarettes per day

159

2.6

17.2

11.2

1.0

0.086

0, 0.270

Summary of Diabetes Self Care Activities Measure

General diet score

953

13.7

58.4

33.3

1.2

0.017

0, 0.048

Specific diet score

980

14.1

52.2

23.9

0.8

0.011

0, 0.038

Exercise score

992

14.3

34.6

32.7

1.2

0.029

0, 0.062

Blood glucose self-monitoring score

933

13.5

57.9

38.9

1.5

0.051

0.010, 0.093

Foot care score

990

14.3

44.2

35.5

1.2

0.002

0, 0.026

Literacy: Short Test of Functional Health Literacy in Adults

Test score (0–36 points)

1002

14.4

29.7

9.6

0.3

0.017

0, 0.079

Inadequate (0–16) (%)

1002

14.4

10.5

 

1.0

0.011

0, 0.039

Adequate (23–36) (%)

1002

14.4

82.9

 

1.5

0.037

0.002, 0.073

Comorbidity

Congestive heart failure (%)

1006

14.5

17.1

 

1.4

0.025

0, 0.057

Coronary artery disease (%)

1006

14.5

19.3

 

1.4

0.024

0, 0.056

Peripheral vascular disease (%)

1006

14.5

8.7

 

1.0

0.006

0, 0.032

Stroke (%)

1006

14.5

11.7

 

1.1

0.006

0, 0.032

Dementia (%) †

1006

14.5

0.9

 

0.3

0 §

0, 0.024

Asthma (%)

1006

14.5

20.2

 

1.4

0.014

0, 0.043

Arthritis (%)

1006

14.5

14.1

 

1.1

<0.001

0, 0.024

Peptic ulcer disease (%)

1006

14.5

14.3

 

1.2

0.012

0, 0.040

Cirrhosis (%)

1006

14.5

1.9

 

0.3

0 §

0, 0.024

Paralysis (%)

1006

14.5

3.0

 

0.6

0.006

0, 0.032

Renal disease (%)

1006

14.5

5.0

 

0.6

0 §

0, 0.024

Microvascular complications of diabetes (%)

1006

14.5

16.9

 

1.2

0.012

0, 0.040

Cancer (%)

1006

14.5

11.9

 

1.0

0 §

0, 0.024

Leukemia (%) †

1006

14.5

0.6

 

0.2

0 §

0, 0.024

Lymphoma (%) †

1006

14.5

0.5

 

0.3

0.018

0, 0.048

Metastatic cancer (%) †

1006

14.5

0.7

 

0.3

0 §

0, 0.024

HIV disease (%) †

1006

14.5

0.1

 

0.1

0 §

0, 0.024

Depression (%)

1006

14.5

35.0

 

1.7

0.007

0, 0.033

Comorbid condition count

1006

14.5

1.8

1.7

0.1

0.031

0, 0.065

Self-reported comorbidity questionnaire score (0–54)

1006

14.5

3.6

3.9

0.2

0.032

0, 0.066

Cardiovascular disease (%)

1006

14.5

30.9

 

1.6

0.018

0, 0.048

Functional status

SF-12 Physical Component Summary score (0–100)

986

14.2

41.2

12.4

0.5

0.028

0, 0.062

SF-12 Mental Component Summary score (0–100)

986

14.2

50.0

10.7

0.4

0.032

0, 0.061

Patient Health Questionnaire-9 depression score (0–27)

591

11.7

4.1

5.0

0.2

0.006

0, 0.044

Complications of diabetes

Foot ulcer (%)

992

14.3

11.3

 

1.0

0.009

0, 0.036

Vision problems (%)

950

13.7

20.1

 

1.3

0 §

0, 0.025

Foot or leg pain (%)

943

13.6

30.9

 

1.8

0.023

0, 0.055

Stomach emptying problems (%)

901

13.0

6.2

 

0.8

0.003

0, 0.030

Sexual problems (%)

923

13.3

26.4

 

1.4

0 §

0, 0.026

Kidney problems (%)

490

10.3

9.2

 

1.4

0.040

0, 0.096

Medications

Insulin (%)

1006

14.5

18.6

 

1.4

0.014

0, 0.042

Oral hypoglycemic agent (%)

1006

14.5

66.6

 

1.7

0.022

0, 0.053

Total medication count (0–29)

1006

14.5

8.8

4.5

0.2

0.028

0, 0.061

Prescription medication count (0–24)

1006

14.5

6.7

3.8

0.2

0.055

0.014, 0.095

Non-prescription medication count (0–15)

1006

14.5

2.0

2.4

0.1

0.059

0.017, 0.101

Audit of Diabetes-Dependant Quality of Life

Do physically

985

14.2

-1.9

2.6

0.1

0.001

0, 0.025

Confidence in ability

982

14.2

-2.0

2.7

0.1

0.004

0, 0.030

Motivation

981

14.2

-1.9

2.7

0.1

0 §

0, 0.025

Freedom to eat

985

14.2

-2.8

2.9

0.1

<0.001

0, 0.025

Enjoyment of food

986

14.2

-2.5

2.9

0.1

0 §

0, 0.025

Future

984

14.2

-0.6

3.8

0.1

0 §

0, 0.025

Freedom to drink

983

14.2

-1.5

2.4

0.1

0 §

0, 0.025

Dependence

982

14.2

-0.6

2.8

0.1

0.004

0, 0.029

Working life

981

14.2

-1.5

2.3

0.1

0.014

0, 0.042

Family life

985

14.2

-0.6

2.7

0.1

0.035

0, 0.070

Social life

983

14.2

-0.9

2.0

0.1

0 §

0, 0.025

Sex life

978

14.1

-1.0

2.4

0.1

0.020

0, 0.051

Physical appearance

980

14.1

-1.1

2.3

0.1

0.012

0, 0.041

Holidays/Leisure

983

14.2

-1.5

2.5

0.1

0 §

0, 0.025

Travel

981

14.1

-1.6

2.6

0.1

0.022

0, 0.054

Society reaction

977

14.1

-0.5

1.6

0.1

0.026

0, 0.058

Finances

978

14.1

-1.7

2.7

0.1

0.009

0, 0.037

Average weighted impact

990

14.3

-1.5

2.0

0.1

0.004

0, 0.029

Resource utilization

Endocrinologist in last year (%)

971

14.0

15.9

 

2.0

0.089

0.037, 0.140

Dietician in last year (%)

984

14.2

34.3

 

1.8

0.018

0, 0.048

Podiatrist in last year (%)

984

14.2

23.8

 

1.6

0.022

0, 0.054

Diabetes Educator in last year (%)

970

14.0

23.8

 

1.8

0.041

0.004, 0.078

Ophthalmologist in last year (%)

944

13.6

60.4

 

2.1

0.041

0.003, 0.079

Diabetes class in last year (%)

999

14.4

35.0

 

1.9

0.035

0.002, 0.073

Emergency Room visits in last year (mean)

994

14.3

0.64

1.46

0.05

0.015

0, 0.044

Health professional visits in last month (mean)

991

14.3

1.63

2.39

0.08

0.035

0, 0.070

  1. N = Subjects analyzed; No = Number per cluster; SD = standard deviation of mean; SE = standard error adjusted for clustering; ICC = Intra-cluster (intra-practice) correlation coefficient.
  2. *In 39 cases in which LDL could not be estimated because triglycerides were over 400 mg/dl, LDL was assumed to be over 100 mg/dl.
  3. † Because only a few subjects have this condition, the ICC may not be estimated consistently.
  4. §The method used truncates the estimate of ICC (and its CI) at 0 for some values that may be negative.
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BMC Medical Research Methodology

ISSN: 1471-2288

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