Table 1 shows the pooled summary statistics for the 9,444 Australian adults. The mean score for the eight domains of the SF-36 were 76.35 (SD = 25.60) for PF, 71.16 (SD = 40.06) for RP, 78.92 (SD = 36.43) for RE , 78.33 (SD = 25.53) for SF , 72.30 (SD = 18.36) for MH, 54.94 (SD = 20.71) for VT, 65.87 (SD = 25.47) for BP, and 60.57 (SD = 21.48) for GH. The mean component summary measures (PCS and MCS) and health utility index (SF-6D) derived from the SF-36 were 45.78 ± 11.38, 47.72 ± 11.26, and 0.73 ± 0.13 (mean ± SD), respectively. Among the study sample, over one quarter (27%) have at least one chronic condition, followed by two (15%), three (7%), and more than three (4%) comorbid chronic diseases. The most common comorbid chronic disease among the obese adults was hypertension (29%), followed by arthritis (24%), asthma (14%), type 2 diabetes (10%), and heart disease (6%).
The results also reveal that almost one-fourth of the participants were over sixty years (25%), over half were female (55%), and married (53%). Of the total, 18% had university qualifications, 61% were employed, 96% were non-indigenous, 61% lived in major cities, 19% were current smoker, 22% drunk over three days a week, and over one third (36%) do not perform physical activities.
Table 1. Pooled characteristics of study participants and subjective health scores
Variables
|
n
|
Mean (SD) / % (95% CI)
|
SF-36 domain scores [Mean (SD)]
|
|
|
Physical functioning (PF)
|
9,444
|
76.35 (25.60)
|
Role physical (RP)
|
9,444
|
71.16 (40.06)
|
Role emotional (RE)
|
9,444
|
78.92 (36.43)
|
Social functioning (SF)
|
9,444
|
78.33 (25.53)
|
Mental health (MH)
|
9,444
|
72.30 (18.36)
|
Vitality (VT)
|
9,444
|
54.94 (20.71)
|
Bodily pain (BP)
|
9,444
|
65.87 (25.47)
|
General health (GH)
|
9,444
|
60.57 (21.48)
|
SF-36 component summary scores [Mean (SD)]
|
|
|
PCS
|
9,444
|
45.78 (11.38)
|
MCS
|
9,444
|
47.72 (11.26)
|
SF-6D
|
9,444
|
0.73 (0.13)
|
Number of comorbid chronic diseases (from the study checklist)
|
|
|
0
|
4,452
|
47.14 (46.14-48.15)
|
1
|
2,556
|
27.06 (26.18-27.97)
|
2
|
1,400
|
14.82 (14.12-15.56)
|
3
|
673
|
7.13 (6.62-7.66)
|
3+
|
363
|
3.84 (3.47-4.25)
|
Heart disease
|
|
|
No
|
8,869
|
93.91 (93.41-94.38)
|
Yes
|
575
|
6.09 (5.62-6.59)
|
Circulatory disease
|
|
|
No
|
9,112
|
96.48 (96.09-96.84)
|
Yes
|
332
|
3.52 (3.16-3.91)
|
Hypertension
|
|
|
No
|
6,677
|
70.7 (69.77-71.61)
|
Yes
|
2,767
|
29.3 (28.39-30.23)
|
Type 1 diabetes
|
|
|
No
|
9,311
|
98.59 (98.33-98.81)
|
Yes
|
133
|
1.41 (1.19-1.67)
|
Type 2 diabetes
|
|
|
No
|
8,472
|
89.71 (89.08-90.3)
|
Yes
|
972
|
10.29 (9.7-10.92)
|
Asthma
|
|
|
No
|
8,088
|
85.64 (84.92-86.33)
|
Yes
|
1,356
|
14.36 (13.67-15.08)
|
Bronchitis
|
|
|
No
|
9,206
|
97.48 (97.14-97.78)
|
Yes
|
238
|
2.52 (2.22-2.86)
|
Arthritis
|
|
|
No
|
7,176
|
75.98 (75.11-76.84)
|
Yes
|
2,268
|
24.02 (23.16-24.89)
|
Cancer
|
|
|
No
|
9,103
|
96.39 (95.99-96.75)
|
Yes
|
341
|
3.61 (3.25-4.01)
|
Age
|
|
|
15-25 years
|
1,001
|
10.6 (9.99-11.24)
|
26-45 years
|
3,175
|
33.62 (32.67-34.58)
|
46-60 years
|
2,903
|
30.74 (29.82-31.68)
|
>60 years
|
2,365
|
25.04 (24.18-25.93)
|
Gender
|
|
|
Male
|
4,270
|
45.21 (44.21-46.22)
|
Female
|
5,174
|
54.79 (53.78-55.79)
|
Civil Status
|
|
|
Single
|
3,487
|
36.92 (35.95-37.9)
|
Married
|
4,998
|
52.92 (51.91-53.93)
|
De-facto
|
959
|
10.15 (9.56-10.78)
|
Education
|
|
|
Year 12 and below
|
4,281
|
45.33 (44.33-46.34)
|
Certificate courses
|
3,428
|
36.3 (35.33-37.27)
|
University qualifications
|
1,735
|
18.37 (17.6-19.17)
|
Household income quintile
|
|
|
Quintile 1
|
1,889
|
20 (19.21-20.82)
|
Quintile 2
|
1,889
|
20 (19.21-20.82)
|
Quintile 3
|
1,889
|
20 (19.21-20.82)
|
Quintile 4
|
1,889
|
20 (19.21-20.82)
|
Quintile 5
|
1,888
|
19.99 (19.2-20.81)
|
Labour force status
|
|
|
Employed
|
5,803
|
61.45 (60.46-62.42)
|
Unemployed
|
341
|
3.61 (3.25-4.01)
|
Not in the labour force
|
3,300
|
34.94 (33.99-35.91)
|
Indigenous status
|
|
|
Non-indigenous
|
9,076
|
96.1 (95.69-96.48)
|
Aboriginal/Torres Strait Islander
|
368
|
3.9 (3.52-4.31)
|
Location
|
|
|
Major city
|
5,741
|
60.79 (59.8-61.77)
|
Regional
|
3,544
|
37.53 (36.55-38.51)
|
Remote
|
159
|
1.68 (1.44-1.96)
|
Smoking status
|
|
|
Never smoked
|
4,500
|
47.65 (46.64-48.66)
|
Ex-smoker
|
3,184
|
33.71 (32.77-34.67)
|
Current smoker
|
1,760
|
18.64 (17.86-19.43)
|
Alcohol consumption
|
|
|
Never drink
|
898
|
9.51 (8.93-10.12)
|
Ex-drinker
|
913
|
9.67 (9.09-10.28)
|
Only rarely to 3 days/week
|
5,538
|
58.64 (57.64-59.63)
|
3+ days/week
|
2,095
|
22.18 (21.36-23.03)
|
Physical activity that lasts at least 30 min
|
|
|
Not at all to <1/week
|
3,392
|
35.92 (34.96-36.89)
|
1-3 times/week
|
3,701
|
39.19 (38.21-40.18)
|
≥4 times/week
|
2,351
|
24.89 (24.03-25.78)
|
Table 2 presents the mean values of each of the eight dimensions of SF-36, the summary measures and the health utility index by the number of comorbid chronic diseases. As can be seen, the mean score for all SF-36 dimensions/subscales, composite measures, and health utility index decline with a higher number of chronic diseases. For example, obese people with more than three comorbid chronic diseases had the lowest scores than their counterparts with zero, one, two and three chronic conditions. The respective mean PCS, MCS, and SF-6D scores among the study sample with over three chronic diseases (29.48 ± 9.78, 43.86 ± 11.76, and 0.59 ± 0.11, respectively) were much lower than peers without the comorbid chronic disease (50.77 ± 8.14, 48.02 ± 10.76, and 0.76 ± 0.11, respectively).
Table 2. The SF-36 subscale scores and the summary measures by number of chronic conditions
The SF-36 subscale
and summary measures
|
Number of comorbid chronic diseases
|
0
(Mean ± SD)
|
1
(Mean ± SD)
|
2
(Mean ± SD)
|
3
(Mean ± SD)
|
3+
(Mean ± SD)
|
Physical functioning
|
86.18 (19.64)
|
77.36 (22.83)
|
64.08 (25.89)
|
51.21 (26.98)
|
42.57 (25.29)
|
Role physical
|
84.61 (30.84)
|
72.45 (38.93)
|
54.00 (43.37)
|
38.41 (42.25)
|
24.06 (35.83)
|
Role emotional
|
84.72 (31.63)
|
79.75 (35.39)
|
72.95 (40.29)
|
64.14 (43.25)
|
52.34 (45.31)
|
Social functioning
|
83.82 (22.15)
|
79.34 (24.46)
|
72.38 (27.26)
|
63.84 (29.29)
|
53.62 (27.57)
|
Mental health
|
73.56 (17.50)
|
72.22 (18.74)
|
71.82 (18.86)
|
68.74 (19.77)
|
65.89 (18.91)
|
Vitality
|
58.51 (19.66)
|
55.24 (20.70)
|
51.31 (20.96)
|
46.50 (20.28)
|
38.76 (18.60)
|
Bodily pain
|
75.40 (21.12)
|
65.36 (24.09)
|
54.04 (24.77)
|
45.00 (25.08)
|
36.79 (21.97)
|
General health
|
67.47 (18.30)
|
60.99 (19.73)
|
53.06 (21.65)
|
43.60 (21.88)
|
33.50 (19.79)
|
PCS
|
50.77 (8.14)
|
46.06 (10.12)
|
39.38 (11.44)
|
33.83 (11.40)
|
29.48 (9.78)
|
MCS
|
48.02 (10.76)
|
47.83 (11.40)
|
48.05 (11.81)
|
46.67 (12.14)
|
43.86 (11.76)
|
SF-6D
|
0.76 (0.11)
|
0.73 (0.12)
|
0.69 (0.13)
|
0.64 (0.12)
|
0.59 (0.11)
|
Figure 1 depicts the composite summary scores (PCS and MCS) of the SF-36 by age and gender. It is observed that the PCS score declines with age. Mean PCS score ranged from 52.19 (15-25 years) to 39.48 (60+ years) in males and from 51.26 (15-25 years) to 36.82 (60+ years) in females. However, the MCS score of the study participants went up with age. The mean MCS score ranged from 47.80 (15-25 years) to 50.59 (60+ years) in males and from 42.89 (15-25 years) to 50.83 (60+ years) in females.
Figure 2 offered the visual representation of the health utility index (SF-6D) by age and gender. The figure shows that the study participant’s overall health state slightly declines with age and is generally lower in females. The mean SF-6D score ranged from 0.77 (26-45 years) to 0.70 (60+ years) in males and from 0.72 (15-25 years) to 0.69 (60+ years) in females.
Table 3 displays the association between comorbid chronic diseases and the three summary measures (PCS, MCS and SF-6D) of the SF-36. The estimated coefficients of the number of comorbid chronic diseases and individual chronic diseases concerning the summary measures and health utility index were reported in models 1 to 3. Models 1 and 2 indicate that obese people with a higher number of comorbid chronic diseases scored significantly worse on both PCS and MCS scores than obese people with zero comorbid chronic diseases. Obese people with 1, 2, 3, and 3+ comorbid chronic diseases scored 3 (b = -2.83), 7 (b = -7.37), 11 (b = -11.15), and 14 (b = -14.29) points/units lower on the PCS indicator, and 1 (b = -1.46), 2 (b = -2.34), 4 (b = -3.66), and 6 (b = -6.34) units lower on the MCS indicator, respectively, compared with obese people without comorbid chronic diseases. Models 1 and 2 also report the effects of individual chronic diseases on both PCS and MCS indicators. The result showed that obese people with any of the nine chronic diseases had significantly lower scores on both PCS and MCS indicators. For example, the effect of having cancer in obese people on both PCS (b = -4.08) and MCS (b = -2.27) were lower than counterparts without cancer.
On the SF-6D scale, obese adults with 1, 2, 3 and more than 3 comorbid chronic diseases scored 3 (b = -0.03), 6 (b = -0.063), 10 (b = -0.099), and 14 (b = -0.138) percentage points lower, respectively, compared with obese peers who do not have any chronic disease (model 3). Similarly, the results also showed that obese people having any type of the studied chronic diseases (heart disease, circulatory disease, hypertension, type 1 diabetes, type 2 diabetes, asthma, bronchitis, arthritis, and cancer) scored lower on the SF-6D scale compared with obese people without that particular chronic disease. For example, obese adults with heart disease scored 6 (b = -0.058) percentage points lower on the SF-6D scale than their counterparts without heart disease.
Table 3. GEE estimates of the relationship between chronic conditions and HRQoL
Variables
|
Model 1
PCS, β (95% CI)
|
Model 2
MCS, β (95% CI)
|
Model 3
SF-6D, β (95% CI)
|
Number of comorbid chronic diseasesa
|
|
|
|
0 (ref)
|
|
|
|
1
|
-2.83*** (-3.28, -2.38)
|
-1.46*** (-1.99, -0.92)
|
-0.030*** (-0.036, -0.024)
|
2
|
-7.37*** (-7.96, -6.77)
|
-2.34*** (-3.04, -1.63)
|
-0.063*** (-0.070, -0.055)
|
3
|
-11.15*** (-11.95, -10.36)
|
-3.66*** (-4.60, -2.71)
|
-0.099*** (-0.109, -0.089)
|
3+
|
-14.29*** (-15.32, -13.26)
|
-6.34*** (-7.56, -5.11)
|
-0.138*** (-0.151, -0.125)
|
Heart diseasea
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-5.09*** (-5.92, -4.25)
|
-3.39*** (-4.33, -2.46)
|
-0.058*** (-0.068, -0.048)
|
Circulatory diseasea
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-6.35*** (-7.4, -5.29)
|
-4.33*** (-5.51, -3.15)
|
-0.070*** (-0.083, -0.057)
|
Hypertensiona
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-3.02*** (-3.49, -2.54)
|
-0.83** (-1.36, -0.29)
|
-0.025*** (-0.031, -0.019)
|
Type 1 diabetesa
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-4.00*** (-5.64, -2.37)
|
-1.20 (-3.04, 0.63)
|
-0.027** (-0.047, -0.007)
|
Type 2 diabetesa
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-3.02*** (-3.68, -2.37)
|
-1.61*** (-2.34, -0.87)
|
-0.029*** (-0.037, -0.021)
|
Asthmaa
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-3.77*** (-4.32, -3.22)
|
-2.47*** (-3.09, -1.85)
|
-0.041*** (-0.047, -0.034)
|
Bronchitisa
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-7.69*** (-8.93, -6.45)
|
-4.87*** (-6.26, -3.48)
|
-0.078*** (-0.093, -0.063)
|
Arthritisa
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-8.5*** (-8.98, -8.02)
|
-1.26*** (-1.83, -0.69)
|
-0.068*** (-0.074, -0.061)
|
Cancera
|
|
|
|
No (ref)
|
|
|
|
Yes
|
-4.08*** (-5.12, -3.04)
|
-2.27*** (-3.43, -1.10)
|
-0.042*** (-0.055, -0.030)
|
*** p<0.001, ** p<0.01, * p<0.05; ref reference category.
a Model adjusted for age, gender, civil status, education, household income quintile, labour force status, race, place of living, smoking status, alcohol consumption, and physical activity
Table 4 summarizes the multiple regression analysis results for the number of comorbid chronic diseases which affect the SF-36 subscales. The results show that a negative correlation persists between comorbid chronic conditions and all the dimensions of SF-36. It indicates that a greater number of chronic diseases were associated with lower scores in all domains of the SF-36. For example, having more than three comorbid chronic conditions were associated with substantial reductions in PF (-26.76 units), RP (-41.67 units), RE (-25.36 units), SF (-25.02 units), MH (-9.87 units), VT (-19.92 units), BP (-29.33 units), and GH (-32.49 units).
Table 4. GEE estimates of the relationship between the status of chronic conditions and the dimensions of the SF-36
Variable
|
Physical functioning,
β (95% CI)
|
Role physical,
β (95% CI)
|
Role emotional,
β (95% CI)
|
Social functioning,
β (95% CI)
|
Mental health,
β (95% CI)
|
Vitality,
β (95% CI)
|
Bodily pain,
β (95% CI)
|
General health,
β (95% CI)
|
Number of
chronic diseases
|
|
|
|
|
|
|
|
|
0 (ref)
|
|
|
|
|
|
|
|
|
1
|
-4.56***
(-5.59, -3.52)
|
-7.87***
(-9.61, -6.12)
|
-4.55***
(-6.28, -2.81)
|
-4.22***
(-5.39, -3.06)
|
-2.94***
(-3.82, -2.06)
|
-4.23***
(-5.19, -3.26)
|
-7.6***
(-8.71, -6.48)
|
-7.12***
(-8.06, -6.18)
|
2
|
-12.7***
(-14.06, -11.34)
|
-20.84***
(-23.13, -18.55)
|
-9.94***
(-12.21, -7.67)
|
-10.29***
(-11.81, -8.76)
|
-4.69***
(-5.84, -3.55)
|
-8.86***
(-10.12, -7.59)
|
-16.41***
(-17.87, -14.95)
|
-15.27***
(-16.5, -14.05)
|
3
|
-21.16***
(-22.99, -19.33)
|
-30.96***
(-34.04, -27.88)
|
-15.57***
(-18.63, -12.52)
|
-16.37***
(-18.42, -14.32)
|
-7.44***
(-8.98, -5.89)
|
-13.05***
(-14.75, -11.35)
|
-22.96***
(-24.92, -20.99)
|
-23.49***
(-25.14, -21.84)
|
3+
|
-26.76***
(-29.13, -24.4)
|
-41.67***
(-45.66, -37.68)
|
-25.36***
(-29.32, -21.41)
|
-25.02***
(-27.68, -22.36)
|
-9.87***
(-11.87, -7.87)
|
-19.92***
(-22.12, -17.71)
|
-29.33***
(-31.88, -26.78)
|
-32.49***
(-34.62, -30.35)
|
Model adjusted for age, gender, civil status, education, household income quintile, labour force status, race, place of living, smoking status, alcohol consumption, and physical activity
*** p<0.001, ** p<0.01, * p<0.05; ref reference category.