186
B. Larsson et al.
In all prediction models, the spread of pain variable was used
as a continuous variable (referred to as being covariate) when
adjusting for spread of pain at T0. A subsequent sensitivity
analysis was also performed, treating spread of pain at T0 as an
ordinal covariate. At the follow-up, approximately 13–31% of
the observations were missing. Regarding pain intensity, missing
cases were calculated based on valid responses instead of the total
sample, since pain-free respondents did not answer this question.
cohort. The response rate at T0 was lower among men, single
people and immigrants (Table I).
At the 2-year follow-up survey (T1), 11,386 individuals (55%
female) completed and returned the questionnaire, which consti-
tuted a total of 73% rate of the 15,563 individuals who responded
to the first survey in 2013; 54.5% were in NP, and 45.5% in the CP
cohort. The response rate at T1 was lower among younger ages,
men, single people, secondary educated, unemployed, not Swe-
dish, lower household income, depression and anxiety (Table I).
Response rate and drop-out analysis for T0 and at 2-year
follow-up (T1)
At baseline (T0), 15,781 individuals (54% female) completed
and returned the questionnaire, a response rate of 46.4%. An-
other 218 subjects were excluded due to missing values to vital
questions (e.g. pain characteristics) of the survey. Hence, the
final response rate at T0 was 45.8%. Of the 15,563 respondents,
56.8% were in the non-pain cohort (NP) and 43.2% in the CP
RESULTS
Descriptive statistics at 2-year follow-up (T1)
Age range at the 2-year follow-up (T1) was 18–87
years (mean age 55.8; SD 17.5 years) and 55% were
female. Additional sociodemographic features at T1
Table I. Sociodemographic characteristics and study measures at baseline (T0), and at 2-year follow-up (T1), and characteristics of
non-participants at both times
Baseline (T0)
Characteristics
Age, years, mean (SD)
Sex, n (%)
Male
Female
Marital status, n (%)
Single
Married
Divorced
Widowed
Educational level, n (%)
Elementary school
Secondary school or vocational training
College or university
Employment status, n (%)
Employment
Unemployment
Country of birth, n (%)
Sweden
Abroad (i.e. immigrant)
Citizenship, n (%)
Swede
Other
Household income, Euros per year, mean (SD)
Pain intensity (NRS7d), mean (SD)
Pain spreading, n (%)
NP
LP
RPM
RPH
WSP
Pain sensitivity (mean PSQ), mean (SD)
Comorbidities, n (%)
Traumatic injuries
Rheumatoid arthritis–osteoarthritis (RA/OA)
Cardiovascular disorders (CVD)
Pulmonary disorders
Gastrointestinal disorders (GI)
Disorders of the CNS
Urogenital disorders
Skin disorders
Tumours/cancer
Metabolic disorders
Depression
Anxiety
Number of
answers
15,563
15,563
Follow-up (T1)
Participants
(n = 15,563)
51.6 (18.5)
Number
of answers
11,384
11,386
7,151 (46.0)
8,412 (54.0)
15,555
55.8 (17.5)
Baseline (T0) Follow-up (T1)
Non-participants
(n = 18,219) Non-participants
(n = 4,177)
–
45.6 (19.5)
5,125 (45.0)
6,261 (55.0) 9,837 (54.0)
8,382 (46.0) 2,026 (48.5)
2,151 (51.5)
3,179
6,105
1,387
715 9,440
6,347
1,802
630 1,851
1,721
411
191
11,386
5,134
7,825
1,762
834
(33.0)
(50.3)
(11.3)
(5.4)
15,256
(27.9)
(53.6)
(12.2)
(6.3)
(51.8)
(34.8)
(9.9)
(3.5)
(44.3)
(41.2)
(9.8)
(4.6)
11,162
3,442 (22.6)
6,225 (40.8)
5,589 (36.6)
15,115
2,491 (22.3)
4,257 (38.2)
4,414 (39.5) –
–
– 871 (21.5)
1,898 (46.9)
1,282 (31.6)
6,213 (56.5)
4,789 (43.5) –
– 2,342 (58.4)
1,671 (51.6)
10,496 (92.2)
890 (7.8) 14,475 (79.5)
3,744 (20.5) 3,597 (86.1)
580 (13.9)
11,194 (98.3)
192 (1.7)
58,419 (35,919)
4.7 (2.0) 16,786 (92.1)
1,433 (7.9)
–
– 4,019 (96.2)
158 (3.8)
51,834 (36014)
4.9 (2.1)
11,002
8,708 (57.6)
6,407 (42.4)
15,563
11,386
14,093 (90.6)
1,470 (9.4)
15,563
15,510
6,870
15,562
Participants
(n = 11,386)
11,386
15,197 (97.7)
366 (2.3)
55,270 (35,157)
4.8 (2.0)
15,415 8,851 (56.9)
2,580 (16.6)
2,989 (19.2)
823 (5.3)
319 (2.0)
3.7 (1.5)
14,887
14,932
14,901
14,972
15,012
15,001
14,883
14,968
14,687
15,000
14,878
14,868 1,506
2,823
3,295
1,614
2,453
2,993
725
1,851
545
1,559
2,092
2,537
(10.1)
(18.9)
(22.1)
(10.8)
(16.3)
(20.0)
(4.9)
(12.4)
(3.7)
(10.4)
(14.1)
(17.1)
11,386
5,305
11,386
11,278 6,201 (54.5)
2,046 (18.0)
2,359 (20.7)
559 (4.9)
221 (1.9)
3.9 (1.5) –
–
–
–
–
–
10,800
10,595
10,766
10,816
10,752
10,865
10,740
10,861
10,635
10,852
10,598
10,570 1,013
2,307
2,719
1,169
1,793
2,218
582
1,356
454
1,223
1,513
1,842 –
–
–
–
–
–
–
–
–
–
–
–
(9.4)
(21.8)
(25.3)
(10.8)
(16.7)
(20.4)
(5.4)
(12.5)
(4.3)
(11.3)
(14.3)
(17.4)
2,364 (56.6)
690 (16.5)
781 (18.7)
247 (5.9)
95 (2.3)
3.8 (1.6)
436
629
700
488
680
754
200
511
160
400
666
830
(11.2)
(16.5)
(18.1)
(12.5)
(17.6)
(19.3)
(5.2)
(13.1)
(4.2)
(10.3)
(17.7)
(21.9)
PSQ: Pain Sensitivity Questionnaire; SD: standard deviation; CNS: central nervous system; NP: no pain, LP: local pain; RPM: Regional Pain-Medium; RPH: Regional
Pain-Heavy; WSP: widespread pain, N: total number of participants.
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