BACk Pain in Elders in Norway (BACE-N); A Prospective Cohort Study of Older People Visiting Primary Care With a New Episode of Back Pain
Conditions: Back Pain
Sponsor: Oslo Metropolitan University

Protocol for the BACE-N registered 9th January 2020 
 
BACk pain in Elders in Norway (BACE-N): a prospective cohort study of older people visiting 
primary care with a new episode of back pain 
 
Scientific board: Chris Maher, Bart Koes, Manuela Ferreira, Kjersti Storheim, Liv Inger Strand, 
Silje Stensrud, Iben Axen, Thor Einar Holmgaard, Margreth Grotle  
 
Statistical advisor: Milada C. Småstuen 
 
Sponsor: Oslo Metropolitan University, the Norwegian Fund for Post-Graduate Training in 
Physiotherapy, Norway, the Research Unit of the Norwegian Chiropractic Asssociation (ELIB)  
 
Principal Investigator: Margreth Grotle 
 
Registration of study: clinicaltrials.gov 
 
Contents 
Abstract ........................................................................................................................................... 2 
Background ..................................................................................................................................... 3 
Objective and aims .......................................................................................................................... 3 
Methods/design ............................................................................................................................... 5 
Discussion ..................................................................................................................................... 14 
Acknowledgments......................................................................................................................... 15 
References ..................................................................................................................................... 15 
 
 
 
 
 
 

Protocol for the BACE-N registered 9th January 2020 
Abstract  
Back pain represent a considerable burden worldwide, and is predominantly managed in primary 
care. Between 2010 and 2050, the number of people aged 60 years and older will increase by 
56% in developed countries, and this transition will increase the burden of chronic back 
disability. Most previous studies on back pain have excluded people above 60 years of age, 
leading to a large knowledge gap regarding the prognosis of back-related disability and pain in 
older people and which factors influence the transition from acute to chronic stage. Further, back 
pain outcomes and prognostic factors exploredin the few existing studies are not selected to 
capture the burden and characterization of back pain in older people. Therefore, an international 
Consortium (BACk pain in Elders: BACE) was established in 2008 in order to create 
standardised methodology for large cohort studies and share data on the burden of back pain in 
older people. BACE cohort studies have been established in several countries with the primary 
objective to establish the clinical course and burden of back pain in elderly, to identify 
prognostic factors for chronic back pain and disability, and to explore usual care provided in 
primary care. This protocolaims to provide a thorough description of the Norwegian BACE 
cohort study (BACE-N), including the overall statistical analysis plan for responding to the 
specific research questions. The study design is a prospective observational cohort study with 
linked methodological studies within a primary care setting, recruiting 450 patients from three 
main back pain health professionals; general practitioners, physiotherapists and chiropractors. 
The patients respond to a comprehensive questionnaire and undergo a standardised physical 
examination at baseline and are followed by questionnaires at 3, 6, 12 and 24 months after 
inclusion. The BACE-N is planned as a prognosis study, and design and methods used are 
therefore in accordance with the PROGnosis RESearch Strategy (PROGRESS), covering overall 
prognosis research, prognostic factor research, and prognostic model research. Methodological 
studies alongside the prognosis study are conducted in line with the COSMIN recommendations. 
The BACE-N project will provide new knowledge on prognosis of back-related disability and 
pain in elderly people who seek help in the primary healthcare, the clinical course of back pain 
over two follow-up years, including a thorough description of healthcare utilisation and their 
costs, and prognostic factors that influence good or poor prognosis for these people. 
 
 
 

Protocol for the BACE-N registered 9th January 2020 
Background  
 
Back pain represents a considerable burden worldwide, and is predominantly managed in 
primary care (1). Between 2010 and 2050, the number of people aged 60 years and older will 
increase by 56% in developed countries, and this transition will increase the burden of chronic 
back disability. Most previous studies on back pain have excluded people above 60 years of age 
(2), leading to a large knowledge gap regarding the prognosis of back-related disability and pain 
in older people and which factors influence the transition from acute to chronic stage. Further, 
back pain outcomes used in the few existing studies are not selected to capture the burden and 
characterization of back pain in older people. Therefore, an international Consortium (BACk 
pain in Elders: BACE) was established in 2008 in order to create standardised methodology for 
large cohort studies and share data on the burden of back pain in older people (3). The BACE 
study is a large international prospective clinical cohort study, in which people (≥55 years) who 
seek primary care with a new episode of back pain are included. The overall aim is to establish 
knowledge on the burden of back pain in elderly and how it can be managed. The BACE study is 
currently conducted in the Netherlands, Brazil and Norway. A Norwegian arm of the BACE 
(BACE-N) has been established and involves 3 PhD projects. 
 
The background for the BACE can be summed up as follows: the number of elderly is expected 
to steadily increase in the near future and there is lack of knowledge about the prognosis and 
burden of back-related disability and pain in older people and which factors influence the 
transition from acute to chronic stage. Further, back pain outcomes and potential prognostic 
factors used in the few existing studies are not selected to capture the burden and 
characterization of back pain in older people, and older people have often been excluded from 
clinical studies on back pain. 
 
Prognosis research is hampered with many weaknesses and involves certain methodological 
challenges that should be considered (4). In order to ensure high quality of the published papers 
produced from the BACE-N we aim to register this specific protocol, including a statistical 
analysis plan, and report the results from the BACE-N regardless of findings (5).   
 
Objective and aims 
 
The primary objective of the BACE-N is to establish the clinical course and burden of back pain 
and disability in elderly, to identify prognostic factors for chronic back pain and disability, and to 
explore usual care provided in primary care. Specific aims for the BACE-N are: 
 
1. Explore potential differences in baseline characteristics, including main domains of measurements of 
putative prognostic factors and outcomes, across patients who seek general practitioner, physiotherapist and 
chiropractor in primary care  
2. Establish the 1- and 2-year clinical course (overall prognosis) and burden of back-related disability (defined 
as the primary outcome) 
3. Establish the 1- and 2-year clinical course (overall prognosis) and burden of pain (severity, 
location/radiation/neurological signs, stiffness, and use of pain medication) 
4. Describe usual care provided in the primary care (for the initial episode of back pain) and costs due to total 
healthcare utilization (including secondary care such as hospitalisation and institutionalisation) during one 
year of follow-up  

Protocol for the BACE-N registered 9th January 2020 
5. To establish prevalence and incidence of insomnia in these people, and investigate the impact of insomnia 
on back pain and disability outcomes during one year follow-up.                                                                            
6. Assess the association between established prognostic factors in the middle-aged back pain population 
(comorbidity and psychosocial profile) and back-related disability at 1-and 2-years follow-up 
7. Develop and validate a prognostic model for long-term back-related disability at 1- and 2-years follow-up 
in these people 
8. Explore prognostic factors associated with persistent and/or recurrent back pain at 1- and 2 years follow-up 
9. Explore prognostic factors associated with healthcare costs during 1-year of follow-up   
10. Establish the 1- and 2-year incidence of falls and explore prognostic factors associated with falls during 1- 
and 2-year of follow-up.  
11. Assess the clinical course (overall prognosis) of main outcomes (disability, pain, and healthcare costs) 
across patients who seek general practitioner, physiotherapist and chiropractor in primary care.                                                  
12. Assess gender differences in clinical course, prognostic factors and usual care in these people.                                                    
 
Table 1 presents an overview of the planned articles in three PhD projects based on the BACE-
N. In addition to these articles, the BACE-N includes methodological studies of the 
measurements from the original BACE protocol that had to be translated and validated for 
Norwegian patients. These are not included in the present overview. 
 
Table 1: Aims and type of study for planned articles in three PhD theses based on the BACE-N   
Aims in planned articles 
Type of study 
Article I (PhD I): Measuring productivity costs in patients with musculoskeletal disorders: 
measurement properties of the iMTA Productivity Cost Questionnaire 
Methodological study 
using COSMIN guidelines 
Article I (PhD II): The aim of this study is to describe the characteristics of patients aged 55 
years or older visiting a chiropractor, general practitioner or a physiotherapist in the primary 
care with a new episode of back pain. Further, the aim is to examine whether baseline 
characteristics differ between patients visiting the three health professions in primary care.  
Cross-sectional 
comparison of healthcare 
providers recruiting 
patients to the BACE-N 
Article I (PhD III): To explore latent subgroups of patients aged 55≥ seeking primary health 
care using latent class analysis. Second aim: to investigate care seeking behaviours for each 
subgroup. 
Latent class analysis in 
baseline BACE-N 
material. 
Article II (PhD I): Describe usual care and healthcare utilization throughout one year of 
follow-up among elderly people seeking primary care due to a new episode of back pain.  
Secondary aims: Assess the costs of healthcare utilization across patients recruited from 
different health professionals in primary care and across patients with different risk profiles 
according to the STarT Back Screening tool. 
Type I PROGRESS 
 
Article III (PhD I): Explore predictors associated with high costs due to healthcare 
consumption in older people seeking primary care with a new episode of back pain. 
Secondary aim: External validate identified predictors for high costs in the BACE material 
from the Netherlands. 
Type II  PROGRESS 
 
Article II (PhD II): The aim of this study is to establish the 12-month clinical course of 
back-related disability in patients aged 55 years or older visiting a chiropractor, general 
practitioner or physiotherapist with a new episode of back pain. Further, the aim is to 
examine associations between baseline factors (yellow flags, co-morbidity, sleeping 
disturbance) and disability at 12 months (by Roland-Morris Disability Questionnaire).  
Type I and II PROGRESS 
 
Article III (PhD II): The aim of this study is to develop a prognostic model for long-term 
disability (by Roland-Morris Disability Questionnaire) in patients aged 55 years or older 
with a new episode of back pain. The model will make use of individual patient data from 
other BACE cohorts  including Brazil, Netherlands and Norway. 
Type III PROGRESS 
 
Article II (PhD III): To explore trajectories of back pain among older patients seeking 
primary health care according to the subgroups identified in the Latent Class analysis as well 
as the relation to previously established trajectories 
Type I PROGRESS 
Latent class analysis 
 
Article III (PhD III): To identify potential prognostic factors for different back pain 
trajectories in terms of pain intensity and chronicity. 
Type II PROGRESS 
 

Protocol for the BACE-N registered 9th January 2020 
Methods/design 
The study was classified as a quality assessment study by the Norwegian Regional Committee 
for Medical Research Ethics (reference no. 2014/1634/REK vest) and was approved by the 
Norwegian Social Science Data Service (reference no. 42149) in 2015. The BACE-N aims to be 
a multidisciplinary study, involving both general practitioners, physiotherapists and 
chiropractors, as well as patient representatives. A broad network of clinicians and researchers 
are involved in the BACE-N. Patient representatives have been participated to establish BACE-N 
in Norway and the analysis plans, and will participate in the interpretation, communication and 
implementation of findings from the BACE-N.  A pilot study for the BACE-N study was 
conducted from March 2015 until April 2017, including 100 patients. There was no major 
change of the protocol after the pilot, so the recrution of patients to a fullscale BACE-N 
continued. Status today (December 2019) is 420 included patients; 78 from GPs, 157 from PTs, 
and 185 from chiropractors.  
 
a. Study design and setting 
 
This is a prospective observational cohort study with linked methodological studies within a 
primary care setting. The BACE-N is planned as a prognosis study, and design and methods used 
are therefore in accordance with the PROGnosis RESearch Strategy (PROGRESS), covering 
overall prognosis research, prognostic factor research, and prognostic model research (4, 6, 7).    
 
b. Participating patients and cohort study recruitment  
 
The eligible patients for the BACE-N study are all consecutive women and men 55 years of age 
or older who seek primary care (GP, physiotherapist or chiropractor) with a new episode of back 
pain (preceded by 6 months without visiting a primary care provider for similar complaints). 
Patients are excluded from the study if they have a cognitive impairment which precludes them 
from completing the study questionnaires or if they have difficulties speaking and writing 
Norwegian. Patients who have severe mobility impairments (i.e. are wheelchair bound) are 
excluded if they have difficulty in completing the physical examination. A subsample of patients 
who respond and agree to participate in the methodological study will be asked to respond to 
some of the measurements after 2-4 days (test-retest assessment). 
 
The patients are recruited from a range of general practitioners (GPs), physiotherapists (PTs), 
and chiropractors working in the primary care in Norway. Test stations are established within 
each recruiting area, organised by a local research assistant, where all inclusion/baseline 
procedures will be conducted. Individual patients who consult with back pain are informed about 
the study and invited to participate. Patients who fit the eligibility criteria and complete the 
consent to participate respond to a comprehensive baseline questionnaire and undergo a 
standardised physical examination. The questionnaire is preferably completed electronically 
(Infopad), but a paper version is also available for patients who are not familiar with an 
electronic data collection. Patients will not receive any payment or financial incentive to take 
part, except that the clinical examination is free and that they receive general advice according to 
guidelines after the examination. The patients receive care as usual for the back pain episode 
they seek help for.  
 

Protocol for the BACE-N registered 9th January 2020 
c. Cohort study follow-up 
All patients who have signed consent to take part and have responded to the questionnaire and 
gone through the physical examination at baseline will be sent follow-up questionnaires 3, 6, 12 
and 24 months after inclusion. The follow-up questionnaire will preferably be completed over 
email through the Infopad system, or posted if necessary. Up to two reminders are sent by email 
or sms for those who do not respond to the questionnaire. The high frequency of follow-ups 
during the first year will minimise recall bias. The reasons given for drop out will be recorded for 
individuals who cease study participation.  
 
d. Physical examination at baseline 
The content of the physical examination in BACE-N at baseline is described in Table 2. This 
standardized protocol for the physical examinations in BACE-N adhere to a large extent to the 
procedures described in the original published BACE protocol (3) with some exceptions; we did 
not include bone quality of the heel, C-reactive protein levels (blood sample), or imaging (X-
rays, MRI, CT) due to costs of these physical examinations and also due to practical 
considerations, as many of the BACE-N patients are recruited from physiotherapists and 
chiropractors. The data from the physical examination at baseline will be used to describe the 
BACE-N material with respect to diagnostic triage; possible red flag conditions (cancer, 
vertebral infection, fracture, cauda equine syndrome, inflammatory disorder), nerve root  
involvement (radiculopathy and spinal stenosis), and non-specific low back pain. The Pain 
Response to Activity and Position (PRAP) is a screening test based on patient reports of changes 
in low back pain in response to activity and posture that could be used to place patients into 
diagnostic categories such as radiculopathy and spinal stenosis. This screening can be used as a 
first step in the diagnostic process to focus and direct the clinical examination among patients 
with low back pain (8). The accuracy of the PRAP when used in participants included in the 
BACE-N will be presented (see Appendix I).   
The physical examination also includes some movement tests that will be used to provide a 
thorough description of functional status profiles. The Back Performance Scale (9) and the timed 
up and go (TUG) test (10) will also be used as potential prognostic factors for some of the 
outcome measures listed below. Since this is an observational study there will be no interference 
with the care given by the primary healthcare providers. However, the usual care provided by 
these and other healthcare utilization used by the patients during follow-up will be recorded 
during the follow-ups (see below).  
 
 
 

Protocol for the BACE-N registered 9th January 2020 
Table 2: Content of the physical examination at baseline   
History taking 
Inspection and movement tests 
Pain location and radiation  
Height and weight 
Pain severity (NRS 0-11) 
Standing posture, scars or other abnormalities 
Leg pain > back pain 
Heberden’s and Bouchard’s nodules 
Paresthesia of the foot/toes 
Palpation paravertebral muscles 
Neuropathic pain (DN4) 
Palpation and percussion spinous processes and sacroiliac joint 
History of back pain 
Ankel and knee tendon reflex 
Pain response to activity 
Hypesthesia or hypalgesia of foot/toes 
Pain response to coughing/sneezing 
Neuropathic pain tests (DN4) 
Systematically unwell 
Weakness, standing on heel/toes 
Fever 
Finger-floor distance, range and pain 
Unexplained weight loss > 4.5 kg 
Latero-flexion: range and pain  
Sudden decrease in height 
Upper body rotation: range and pain 
Comorbidity, e.g. urine tract or skin infection, diagnosis of osteoporosis 
Muscular strength m. quadriceps 
 
Lasegue and crossed Lasegue test 
  
Exo- and endorotation of the hip: range and pain  
 
Time Up and Go (TUG) 
 
Back Performance Scale (BPS) 
 
e. Measurements of outcome and prognostic factors 
The measurements included in the comprehensive questionnaire in the BACE-N and timing of 
data collection are presented in Table 3. These adhere to the standardized protocol in the original 
published BACE protocol with some exceptions; first, we have also included the STartBack 
screening tool as a potential prognostic factor. Second, we have included one outcome measure 
on insomnia at 12 months follow-up, since insomnia is a source of great concern among elderly 
people (11). Third, we did not include SF36 (12) as an outcome measure at the follow-ups due to 
the length of this questionnaire. It is only included at baseline in order to describe the population 
with respect to burden of back pain, and to use the components as potential prognostic factors.   
 
Importantly, the number of variables included in Table 3 does not reflect the number of 
independent variables in the statistical analyses. Many of the variables listed in Table 3 will form 
basis for broader constructs in the analyses of the BACE-N material. For example, the variables 
listed in the domain “Health care utilization” will be summarised to one outcome labelled “cost 
of healthcare”. Similarly, other variables will be grouped together to cover a broader construct, 
e.g. variables related to back pain history and pain/symptoms measures will be used to define 
patients who have recovered or not during the follow-ups. Only a reasonable selection of 
potential prognostic variables will be used depending upon previous findings in the literature and 
type of analysis that will be carried out (e.g. Type I, II or III prognosis study). Finally, although 
the variables in Table 3 are listed as outcome and potential prognostic variables, these might 
change role in some of the planned papers for the BACE-N: for example, in methodological 
studies of the PRAP, PWQ, BBQ, and StarT Back, these measures will be defined as outcome 
measures for the specific planned paper. Vica versa some of the variables mentioned as outcome 
measures will be used as potential prognostic factors in some papers, for example pain and 
disability measures will be used as potential prognostic factors in the planned Article III (PhDI) 
(Table 1).   
 
 
 

Protocol for the BACE-N registered 9th January 2020 
Table 3: Measurements and timing of key outcome and prognostic measures in the BACE-N   
 
Baseline 
3 
mo. 
6 
mo. 
12 
mo. 
24 
mo. 
Sociodemographic variables 
 
 
 
 
 
Age  
X 
 
 
 
 
Gender  
X 
 
 
 
 
Marital status 
X 
 
 
 
 
Ethnicity  
X 
 
 
 
 
Educational level 
X 
 
 
 
 
Employment status  
X 
X 
X 
X 
X 
Key outcome measures 
 
 
 
 
 
Disability (RMDQ)* 
X 
X 
X 
X 
X 
Pain severity back and leg (NRS)* 
X 
X 
X 
X 
X 
Overall recovery** 
 
X 
X 
X 
X 
Health care utilization and costs*   
 
 
 
 
 
Back medication (type, frequency)   
X 
X 
X 
X 
X 
Consultation to healthcare professionals, numbers and type 
X 
X 
X 
X 
X 
Treatment type provided by healthcare professionals 
X 
X 
X 
X 
X 
Diagnostic examinations (blood sample, diagnostic imaging, other)  
X 
X 
X 
X 
X 
Hospitalisation/Institutionalisation  
X 
X 
X 
X 
X 
Operation (back) 
 
 
 
X 
X 
Insomnia (Bergen Insomnia Scale)  
X 
 
 
X 
 
Falls (frequency and cause) 
X 
X 
X 
X 
X 
Potential prognostic factors 
 
 
 
 
 
Back pain history; onset of symptoms, frequency, duration, radiation, weakness, 
neurological symptoms and signs (neuropathic pain, morning stiffness), and 
widespreadness of pain* 
X 
X 
X 
X 
X 
Falls efficacy (FES-I)* 
X 
X 
X 
X 
X 
Comorbidity (Self-Administered Comorbidity Questionnaire)  
X 
 
 
 
 
Physical workload at work (PWQ) 
X 
 
 
 
 
Productivity loss (iPCQ)* 
X 
 
 
X 
X 
Job satisfaction  
X 
 
 
 
 
Self-reported physical activity (IPAQ-SF) 
X 
 
 
 
 
Alcohol use (subscale AUDIT) 
X 
 
 
 
 
Smoking  
X 
 
 
 
 
Sleep quality (subscale PSQI) 
X 
 
 
 
 
Kinesiophobia (FABQ) 
X 
 
 
 
 
Pain Catastrophizing (PCS) 
X 
 
 
 
 
Back Beliefs (BBQ)* 
X 
X 
X 
X 
X 
Emotional well-being (CES-D)  
X 
 
 
 
 
STarT Back Questionnaire* 
X 
X 
X 
X 
X 
Expectation of recovery from pain within 3 months 
X 
 
 
 
 
Expectation of returning to work within 3 months 
X 
 
 
 
 
Health-related QOL (SF36)* 
X 
 
 
 
 
*some of these measures will be used both as outcome and prognostic factors 
**defined by NRS and RMDQ, as well as Global Perceived Effect (GPE) scale and Patient Acceptable Symptom 
State (PASS); see text for description of methods 
 
 
 

Protocol for the BACE-N registered 9th January 2020 
Outcome measures: Six key outcome measures are listed in Table 3: these are selected because 
they reflect different core aspects of back pain in elderly according to a healthcare perspective, 
taking into account pain and disability, overall recovery during follow-up, healthcare utilization, 
insomnia, and falls.  
 
1) Pain-related disability assessed by the Roland Morris Disability Questionnaire (RMDQ) (13) 
is the primary outcome of the BACE-N. The RMDQ is a widely used back-specific patient-
reported measure of pain-related disability (0 = no disability, 24 = totally disabled). The 
Norwegian version has been validated and found to have good measurement properties when 
used among patients with low back pain (14, 15). 
 
2) Pain severity (by numerical rating scale, NRS) for back and leg pain, scored from 0 (no pain) 
to 10 (maximum pain). NRS has been widely used to evaluate pain and has proven to be 
preferable when examining low back pain patients (16), also for Norwegian patients (15). 
 
3) Overall recovery will be defined specifically for this population (elderly seeking help for back 
pain) by using the two first key outcomes, NRS and RMDQ, as well as the global perceived 
effect (GPE) scale (7-point ordinal scale) (17)  and the Patient acceptable symptomatic state 
(PASS) (5-point ordinal scale) (18).While the GPE aims to reflect the overall change in a 
condition, here back pain, over a period of time, the PASS has been defined as the highest level 
of symptom beyond which patients consider themselves well (18). Different generic scales 
assessing “overall change” and “recovery” have shown good test-retest reliability in several 
musculoskeletal disorders, including back pain (19).  We will conduct analysis based on 3 and 12 
months follow-up data using same method as in Kamper et al 2010 (pain numerical rating scale 
and Roland Morris Disability Questionnaire) (19), plus by using the GPE and PASS scales, in 
order to identify the most accurate measure for overall recovery in the present BACE-N material 
(see Appendix I). 
 
4) Costs due to healthcare utilization (see variables in Table 3) will be summed up for one year 
of follow-up. Health care utilization will be described in terms of type and frequency. 
 
5) Number of falls during follow-up, including description of cause of the fall 
 
6) Insomnia (Bergen Insomnia Scale) will be used to assess the occurrence of insomnia (20). 
Bergen Insomnia Scale consists of 6 items, of which the first three pertain to sleep onset, 
maintenance, and early morning wakening insomnia, respectively. The last three items refer to 
not feeling adequately rested, experiencing daytime impairment, and being dissatisfied with 
current sleep. This scale was validated in three samples, 320 students, 2,645 community persons, 
and 225 patients, and was found to have good psychometric properties. It is one of very few 
insomnia scales which provide normative data for comparisons and which has been validated 
against subjective as well as polysomnographic data. 
 
Putative prognostic factors: The potential prognostic factors cover different types of variables 
according to a biopsychosocial model. Sociodemographic, lifestyle and clinical factors are listed 
in Table 3 and are based on brief questions tested in the first BACE cohort in the Netherlands 
and in the pilot study in Norway.  The following prognostic factors are included: 

Protocol for the BACE-N registered 9th January 2020 
 
Back pain history covers a range of aspects related to the present back pain episode of which the 
patient seek help; the questions related to self-report of  onset of symptoms, frequency, duration, 
and radiation are taken from the Norwegian version of the Core Outcome Measures Index 
(COMI) (21). Psychometric properties of all single core items included in COMI and the 
composite index score is found to be satisfying and as good as those for corresponding full-
length questionnaire (22, 23). The self-reported items concerning weakness and other 
neurological symptoms and signs (neuropathic pain, morning stiffness) are taken from the Spinal 
Stenosis Measure Symptom subscale, developed by Stucki G et al 1995 (24), which also has 
been translated and validated for Norwegian patients with spinal stenosis (25).  Three items  
regarding stiffness in the back are taken from the KOOS (26). All the variables listed under the 
category “back pain history” will together with the examination variables in Table 2 be used to 
identify patients with nerve root involvement in terms of radiculopathy and spinal stenosis.  
 
In addition, widespreadness of pain will be defined based on the McGill pain drawing (27), the 
Norwegian version (28). ACRs revised criteria for the definition of chronic widespread pain will 
be used (29). Fear of falling will be assessed by the Fall Efficacy Scale International 
Questionnaire (FES-I)) developed by Yardley L et al. (2005) (30) and translated to Norwegian 
by Helbostad JL et al (31), which was found to have good psychometric properties when used in 
an ageing population. Comorbidity will be assessed by the Self-Administered Comorbidity 
Questionnaire (SCQ) (32), which is a 14-item measure of comorbidity for clinical and health 
services research settings. An individual can receive a maximum of 3 points for each medical 
condition: 1 point for the presence of the problem, another point if he/she receives treatment for 
it, and an additional point if the problem causes a limitation in functioning. Because there are 12 
defined medical problems and 3 optional conditions, the maximum score totals 45 points if the 
open‐ended items are used and 36 points if only the close‐ended items are used. 
 
Physical workload will be assessed by the Physical Workload questionnaire (PWQ) (33), which 
has been translated to Norwegian by the BACE-N project group. It consists of 25 items and two 
subscales (heavy physical workload and long-lasting postures and repetitive movements). The 
psychometric properties of the PWQ is currently investigated in a methodological study base on 
a subsample of the BACE-N (master thesis). Productivity loss will be assessed by the 
iProductivity Cost Questionnaire (iPCQ), which scores three aspects of work and productivity 
loss; absenteeism, presenteeism and unpaid work (34). The iPCQ is a revised version of the 
Prodisq and Disease questionnaire, which is listed in the original BACE protocol and is 
recommended by the original developers (35). The iPCQ has been translated and culturally 
adapted, and found to have good measurement properties when used among Norwegian patients 
with long-term musculoskeletal disorders (36). Job satisfaction is assessed by one item from the 
Job Content Questionnaire (37). Physical activity will be measured by the short form of the 
International Physical Activity Questionnaire (IPAQ-SF) (38), which comprises a set of 4 
questionnaires.  IPAC has been translated to Norwegian and used in the Norwegian population 
(39). The short version used in BACE-N has been used in a large survey of the Norwegian 
population, the HUNT survey (40). Three items regarding frequency of alcohol taken from the 
AUDIT tool was used (41), and three items regarding smoking habits was used. The items were 
translated after the BACE original protocol (3). Sleep quality was assessed by two items from the 
Pittsburg Sleep Quality Index (PSQI, item 5 and 6) (42).  

Protocol for the BACE-N registered 9th January 2020 
 
Several aspects of emotional and cognitive functions are assessed: Kinesiophobia or fear 
avoidance behaviour is assessed by the Fear Avoidance Beliefs Questionnaire, physical activity 
subscale (FABQ-PA) (43). The FABQ-PA consists of four questions aimed towards physical 
activity, scored on a 7-point ordinal scale, which are summed up to a sum score, ranging from 0 
(no fear) to 24 (maximum fear). The questionnaire has been translated into Norwegian and has 
shown acceptable psychometric properties in Norwegian patients with low back pain (44). The 
Pain Catastrophising Scale (PCS) includes 13 items that focus on thoughts and feelings about 
pain (45). A Norwegian version tested on patients with back pain has demonstrated acceptable 
psychometric properties (46). The Back Beliefs Questionnaire was developed by Symonds TL et 
al. (47), and consists of 14 items regarding beliefs about the inevitable consequences of back 
pain. BBQ has been used to predict recovery rate from back pain (48, 49), and in population 
studies assessing public attitudes and effectiveness of educational campaigns (50, 51, 52). The 
Norwegian version has been translated by Grotle M og Munk R, and demonstrated acceptable 
test-retest reliability and good construct validity when used in elderly patients with back pain 
(53). Emotional well-being is assessed by the depression scale of Center for Epidemiologic 
Studies Depression Scale (CES-D), which has been widely used in studies of late-life depression. 
Psychometrick properties are generally favourable (54). The Norwegian version of the CES-D 
has been used among elderly patients in order to measure depression symptoms (55). Keele 
StarT Back Screening Tool, developed by Hill JC et al in 2008 (56), is a brief 9-item tool, 
designed to screen primary care patients with low back pain for prognostic indicators that are 
relevant to initial deceision making. The tool was translated by Storheim K og Grotle M in 2012, 
and has shown to have an acceptable accuracy in distinguishing between low back pain patients 
who have recovered or not after 1 year of follow-up (57). In addition, two items on expectations 
are included: one on recovery and one on return-to-work; both assessed on a 5-point scale. The 
items are translated after the BACE original protocol (3).  
 
Finally, health-related quality-of-life by the SF-36, which is a self administered questionnaire 
containing 36 items. It measures health on eight multi-item dimensions, covering physical 
functioning, social functioning, role limitations (physical problems), role limitations (emotional 
problems), mental health, vitality, pain, and overall evaluation of health (12). The Norwegian 
version of the SF-36 was was included only at baseline due to the length of this questionnaire, 
and also due to good data showing that data-completeness in the general population in Norway 
strongly declined with increasing age (58). The authors, Loge and Kaasa, emphasized that 
caution should be exercised when assessing subjective health or employing the norms among 
subjects aged 70 years or over.  
 
f. Cohort study sample size 
The sample size calculation is based on current data from the BACE-N, which involves 269 
patients with completed 12-months follow-up. Our primary outcome measure, RMDQ, has a 
mean score of 5.2 (SD 5.4). A total of 110 patients (41%) have a score of >5 on the 0-24 RMDQ 
scale, which is often used as a cut-off for persistent disability. Assuming the current proportions 
of persistent disability is stable throughout the data collection, a sample size of 360 patients will 
yield approximately 140 participants with persistent disability at 12 months. If we estimate a 
drop-out rate of 20%, we need a total sample size of 450 participants. Thus, a sample size of 450 
participants will allow for 14 prognostic variables in a multivariate logistic regression analyses if 

Protocol for the BACE-N registered 9th January 2020 
we use the “10 events per 1 variable” rule-of-thumb, or 9 variables for the more conservative 15 
events per variable.  The different strategies for variable selection will vary between the different 
planned studies and are further discussed in the Statistical Analysis Plans of the individual 
studies. 
 
g. Statistical analyses 
Weekly checking for completion of data forms in the electronic data system is used to ensure 
quality of the data. The relevant independent and dependent variables for each publication listed 
in Table 1 will be analysed using descriptive statistics. Furthermore, the research questions 
related to overall prognosis research (Type I in PROGRESS) (4), prognostic factor research 
(Type II) (6), and prognostic model research (Type III) (7) will be analysed in accordance with 
recommendations from the PROGRESS framework. For the research questions concerning 
overall prognosis (Type I), defined as describing and explaining future outcomes in relation to 
current diagnostic and treatment practices, the clinical course of our primary (disability by the 
RMDQ) and secondary outcomes (pain, cost of  healthcare utilization , falls and loss of 
independence) will be presented according to type of variable. For example, continuous variables 
as the RMDQ and pain intensity (Numerical rating scale) will be presented by mean and standard 
deviation (SD) for each measurement timepoint, whereas categorical variables such as 
proportions with persistent and/or recurrent pain at follow-ups will be presented by number and 
proportions. When possible we will analyse continuous factors on continuous scales in order to 
increase power (as recommended by the PROGRESS). Further, if we use cut-off points for 
continuous scales the rationale for this decision will be provided.  
 
The overall prognosis of our primary and secondary outcomes will be described in relation to 
time, place and context. We expect the descriptive results from overall prognosis papers in the 
BACE-N to be important for informing patients, clinicians, policy makers, developing (clinically 
meaningful) disease subsets, interpretation and screening research, design and interpretation of 
Type II  and III prognosis research, as well as in design and interpretation of intervention studies, 
including Type IV prognosis research. Research questions concerning assessing prognosis across 
certain subgroups, for example health professionals in primary care (GP, PT, and chiropractors), 
psychosocial profiles («yellow flags») or other phenotypes, will be considered as Type II study 
in the PROGRESS, a prognostic factor type of prognosis study. A prognostic factor is defined as 
any measure that, among people with a given health condition, is associated with a subsequent 
clinical outcome. The repeated measures of the relevant outcomes will be presented for each 
subgroup visually, and will be analysed by GLM analysis for continuous outcome measures and 
logistic regression models for categorical outcome measures. For logistic regression the 
unadjusted and adjusted odds ratio or relative risk with a CI will be presented in order to 
estimate the magnitude of prognostic effect on the outcome.  
 
Further, it will be distinguished between the different phases of prognostic factor research. Many 
of our analyses will involve exploratory prognostic factor research in which many candidates for 
prognostic factors and their association with outcome will be assessed (see Table 1). Identifying 
potential prognostic factors is one of the main objectives for the BACE study, so all candidate 
prognostic factors in the BACE-N are presented in Table 3. For a few specific prognostic factors 
we will carry out both exploratory and confirmatory prognostic research. These concern well-
known and established prognostic factors in the back pain literature such as the impact of co-

Protocol for the BACE-N registered 9th January 2020 
morbidity and psychosocial profile (yellow flags) on back-related disability and persistent and/or 
recurrent pain.  
 
Confirmatory analyses will be carried out in the Dutch BACE material. Analyses of specific 
prognostic factors will be based upon aprior defined hypotheses and a statistical analysis plan 
(SAP) including description of potential confounding factors.  
 
For Type I and II prognosis research conducted in the BACE-N risk of bias will be assessed by 
using the tool Quality In Prognosis Studies (QUIPS) (59). This tool includes questions covering 
6 important criteria when evaluating validity and bias of studies on prognostic factors; study 
participation (does the study sample represent the population of interest?); study attrition (did 
data from participants not lost to follow-up accurately represent the sample?); risk factor 
measurement (is the risk factors similarly measured for all study participants?); outcome 
measurement (is the outcome similarly measured for all the study participants?), confounding 
measurement (are there important potential confounding factors accounted for in the regression 
analyses?), and analyses (is the statistical analyses appropriate and is the primary outcome 
reported?).   
 
Research questions concerning prognostic model research (Type III) is defined to utilise multiple 
prognostic factors in combination to predict the risk of future clinical outcomes in individual 
patients. The prognostic model research aims to provide accurate predictions in order to inform 
patients and caregivers, to support clinical research and to allow more informed decisions to 
improve outcome (ref). For prognostic model analyses we will use predictive models appropriate 
to the type of data each prognostic outcome represents. For example, the repeated pain and 
disability outcomes will be analysed using linear mixed models. Logistic regression models with 
no more than 1 variable per 10 events will be used to develop prognostic models with a 
dichotomous outcome. Multivariate analysis will identify the predictive prognostic factors within 
the predefined domains (e.g. demographic, physical, social and psychological domains). The 
number of factors that will be entered in the multivariate analysis will be condensed by 
univariate pre-testing and omitting highly correlated factors. The prognostic value of both single 
and combined variables will be addressed by calculating sensitivity, specificity, positive and 
negative likelihood ratios in a standard way.  
 
Costs of the provided treatments in primary and secondary health care incurred due to back pain 
will be valued at standard rates published by the relevant professional body or third party payer. 
Costs of community services (e.g. home visits, gym attendance) and other out-of-pocket costs 
(e.g. purchase of a lumbar belt) will be based on the self-reported costs of participants.  
 
In order to explore latent subgroups or clusters in the BACE-N material, we will use Latent Class 
Factor Analysis (LCA). LCA aims to identify subgroups of people who share common 
characteristics in such a way that people within the subgroups have a similar scoring pattern in 
the measured variables, while the difference in scoring patterns between the subgroups are as 
distinctly different as possible (60). Each individual belongs to one subgroup on the basis of the 
highest posterior probability of belonging tothis particular subgroup. In our case, latent class 
modeling seeks the smallest number of subgroups that account for associations of variables such 
as pain and function levels, demographic factors, psychological and behaviour factors measured 

Protocol for the BACE-N registered 9th January 2020 
at baseline. The identified subgroups will then be examined in terms of care-seeking behavior 
and pain development (trajectories) at 3,6, and 12 months. Trajectories identified in previous 
publications will be explord also in these data. Finally, the subgroups will be used to identify 
combinations of prognostic factors for the pain trajectories.  
 
 
Discussion  
This protocol has provided a comprehensive plan for the Norwegian BACE cohort study, the 
BACE-N, including the overall statistical analysis plan for responding to the specific research 
questions outlined in this protocol. Papers published from the BACE-N material will provide 
new knowledge on prognosis of back-related disability and pain in elderly people who seek help 
in the primary healthcare, the clinical course of back pain over two follow-up years, including a 
thorough description of healthcare utilisation and their costs, and prognostic factors that 
influence good or poor prognosis for these people. The BACE-N aims to be a multidisciplinary 
study, involving both general practitioners, physiotherapists and chiropractors, as well as patient 
representatives. 
 
The main strength is that the BACE-N follows standardised methodology for large cohort 
studies, established by the BACE Consortium in 2010 (3). This also implies to share data from 
the BACE-N cohort with other members in the BACE Consortium. Due to the shared and 
standardized methods used in the BACE, this provides researchers of BACE cohorts a unique 
opportunity to validate their findings in BACE materials from other countries. This is far too 
seldom done, and is strongly encouraged by the international group behind the PROGRESS 
framework (4, 6, 7). Furthermore, all plans for the statistical analyses in the BACE-N adhere to 
recommendations from the PROGRESS and the methodological studies are conducted in line 
with the COSMIN recommendations (61). Another strength with the BACE-N study is that we 
aim to recruit patients from the three main back pain health professionals; general practitioners, 
physiotherapists and chiropractors. This provides us an opportunity to compare characteristics, 
clinical course and prognostic factors across these health care providers. The broad network of 
clinicians and researchers involved in the BACE-N, including patient representatives, is 
considered an advantage in order to ensure the clinical importance of the BACE-N along with 
the emphasis on high-quality research methods. The clinical network and patient representatives 
have been participated to establish BACE-N in Norway and the analysis plans, and will 
participate in the interpretation, communication and implementation of findings from the BACE-
N. 
 
The major limitation is that the BACE includes a rather extensive questionnaire, which takes 
approximately 60 minutes to fill in at baseline. The follow-up questionnaires are shorter. This 
might lead to a risk of lack of response and missing items, and hence, low data quality. However 
a pilot study of the first 100 included patients showed a response rate of 88, 87, 80 and 75 % 
respectively at 3, 6, 12 and 24 months follow-up. Another limitation is that we plan many 
articles, leading to many analyses on the same material. This is the main reason why we publish 
this BACE-N protocol. We want to openly address these limitations so the readers of future 
papers from the BACE-N material can make their own assessments of strengths and weaknesses 
of future findings.  

Protocol for the BACE-N registered 9th January 2020 
 
 
Acknowledgments 
 
We thank the initiative takers forming the international BACE consortium: Professor Chris 
Maher, director of the Musculoskeletal Division at The George Institute of Global Health, 
Sydney/ University in Sydney, and Professor Bart Koes, research director of the Department of 
General Practice, Erasums University Medical Center, Rotterdam, conceived the idea of an 
international consortium of cohort studies of Back Pain in the Elders (BACE). We also thank 
professor Manuela Ferreira, University in Sydney, who contributed in the development of the 
BACE protocol as well as in discussions around issues related to existing BACE cohorts. We 
thank the Oslo Metropolitan University, the The Norwegian Fund for Post-Graduate Training in 
Physiotherapy, Norway, and the Research Unit of the Norwegian Chiropractic Asssociation 
(ELIB) for the financial support of the BACE-N. 
 
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