Psychometric evaluation of the Danish version of the Pain Self-Efficacy Questionnaire in patients with subacute and chronic low back pain

Mette Errebo; Martin Oxfeldt; Heidi Tegner; Jan Christensen

doi:10.1515/sjpain-2024-0032

Article Open Access

Psychometric evaluation of the Danish version of the Pain Self-Efficacy Questionnaire in patients with subacute and chronic low back pain

Mette Errebo , Martin Oxfeldt , Heidi Tegner and Jan Christensen

Published/Copyright: October 4, 2024

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From the journal Scandinavian Journal of Pain Volume 24 Issue 1

Abstract

Objective

The Pain Self-Efficacy Questionnaire (PSEQ) is a widely used patient-reported outcome measure designed to assess the level of pain self-efficacy in patients with low back pain (LBP). Although the PSEQ has been translated into Danish, its measurement properties remain unknown in patients with subacute and chronic LBP in Danish outpatient clinics. The aim of this study was to investigate the construct validity, internal consistency, test–retest reliability, and measurement error of the Danish version of the PSEQ in a group of Danish patients with subacute and chronic LBP in a hospital outpatient setting.

Methods

Patients with LBP referred to two Danish outpatient clinics were recruited for this study. Two days after the consultation, the participants were emailed a link to a survey that included the following outcome measures: the PSEQ, the Oswestry Disability Index, the Numeric Pain Rating Scale, and the Tampa Scale of Kinesiophobia. Five days after completion of the survey, a new survey that included the PSEQ was sent to the participants.

Results

In total, 109 participants were included for the analysis of construct validity and internal consistency, with 94 participants included for the analysis of test–retest reliability and measurement error. Construct validity was found to be high and internal consistency was acceptable, with Cronbach’s alpha = 0.93 (95% confidence interval [CI] = 0.91–0.93). Test–retest reliability was found to be good, with an intraclass correlation coefficient (ICC_2.1) of 0.89 (95% CI = 0.82–0.92). The standard error of measurement was calculated to be 4.52 and the smallest detectable change was 12.5 points.

Conclusions

The Danish version of the PSEQ showed acceptable measurement properties in terms of construct validity, internal consistency, and test–retest reliability in a group of patients with subacute and chronic LBP. However, further studies are needed to investigate other aspects of the measurement properties.

Keywords: pain self-efficacy; low back pain; measurement properties; reliability; validity

1 Introduction

Globally, low back pain (LBP) is a common condition, with a prevalence of 568.4 million in 2019 [1]. It is the leading cause of years lived with disability [1,2] and affects a range of dimensions in a patient’s life, such as decreased physical function and reduced work ability, thereby affecting the personal financial situation and health-related quality of life [3,4]. Many factors, such as depression, anxiety, catastrophizing, and self-efficacy, have been linked to the transition from acute to chronic LPB and to the development of persistent disability [3].

Self-efficacy is a psychological construct that describes the confidence or belief in one’s own capacity to achieve goals and specific tasks [5]. According to a systematic review and meta-analysis by Lee et al., self-efficacy is a significant mediator influencing the relationship between pain and disability and therefore is important to target in a rehabilitation setting [6]. In a systematic review from 2018, Martinez-Calderon et al. found that the prognosis of patients with musculoskeletal pain (including LBP patients) is affected by the level of self-efficacy. A higher degree of self-efficacy is associated with higher physical function and work/health status, whereas a lower degree is associated with disability and pain [7]. Moreover, Martinez-Calderon et al. recommend that clinicians should assess the patient’s level of self-efficacy to tailor individualized rehabilitation [7].

Pain self-efficacy is based on self-efficacy and reflects the patient’s confidence in achieving specific goals and everyday activities despite pain [8]. High degrees of pain self-efficacy were associated with higher function (less impairment), lower pain intensity, and less fear of movement in a group of patients with chronic LBP [9]. Pain self-efficacy was among several psychological domains found to be one of the four strongest predictors for disability in a group of patients with LBP, 6 months after a consultation with their general practitioner [10]. Furthermore, pain self-efficacy was found to be an independent predictor for decreased health-related quality of life for a group of patients with chronic LBP attending a 6-month rehabilitation program [11].

Many different self-efficacy questionnaires have been developed and translated into various languages [12]. Among these questionnaires, the Pain Self-Efficacy Questionnaire (PSEQ) is one of two frequently used to measure pain self-efficacy. An expert group concluded that the PSEQ and PSEQ-2 are the most suitable questionnaires to measure pain self-efficacy when measurement properties, feasibility, and personal experience are taken into account [13]. Investigating the measurement properties of outcome measures is important before use in clinical practice and research because psychometric properties might vary across different population samples, settings, and cultural environments [14,15].

The PSEQ was cross-culturally translated into Danish [16] in 2016 and, subsequently, its psychometric properties have been evaluated in Danish patients with chronic LBP (pain for >12 months), finding a high test–retest reliability, with an intraclass correlation coefficient (ICC) of 0.83 [17]. The measurement properties of the PSEQ have not yet been investigated specifically for subacute and chronic LBP patients in a Danish hospital outpatient clinic, thus the aim of this study was to evaluate the psychometric properties of the Danish version of the PSEQ among Danish patients with subacute and chronic LBP in a hospital setting. Specifically, the study focused on evaluating construct validity in relation to functional disability, pain intensity, and kinesiophobia, as well as examining the test–retest reliability, measurement error, and internal consistency of the PSEQ.

2 Methods and materials

2.1 Design

We conducted a measurement properties study using taxonomy and terminology aligned with COSMIN (Consensus-based Standards for the selection of health status Measurement Instruments) [18].

2.2 Setting

LBP patients were identified and screened for eligibility in two Danish outpatient hospital clinics at Rigshospitalet and the Bispebjerg and Frederiksberg Hospital, both part of the Copenhagen University Hospital.

2.3 Participants

Participants had to be ≥18 years of age and with a diagnosis of subacute or chronic LBP for at least 6 weeks to be included in the study.

The exclusion criteria were as follows:

A diagnosis of active cancer, multiple sclerosis, rheumatic inflammatory disease, spinal fracture <3 months, fibromyalgia, complex regional pain syndrome, or other musculoskeletal disorders as a primary diagnosis;
Referred to back surgery;
Not able to read, understand, or fill in the patient-reported outcome measures in Danish; and
Declined to use electronic correspondence.

2.4 Procedure

Eligibility of participants was screened by physiotherapists as part of clinical practice, with possible participants being approached after their first consultation. Oral and written information about the project was given before the patients gave informed consent to participate. If the patients consented to participate, sociodemographic data, including age, sex, pain duration, and recurrency of pain, were obtained.

Two days after the consultation at the hospital, an automatically generated email was sent to the participants’ digital inbox containing a link to a survey (Survey 1) with the following patient-reported outcome measures: the PSEQ, the Oswestry Disability Index (ODI), the Numeric Pain Rating Scale (NPRS), and the Tampa Scale of Kinesiophobia (TSK-11). Furthermore, the survey included questions regarding comorbidity, level of education, work status, smoking status, and anthropometry, from the perspective that the samples can be compared with other samples in future research.

Five days after completion of the first survey, a new survey (Survey 2) with the PSEQ was automatically generated and sent to the participants’ digital inbox. In the case of non-respondence to Survey 1 and Survey 2, automatically generated reminders were sent on the 2 following days. In the case of non-respondence to the generated reminders to Survey 2, the participants received a phone call from the author or a student assistant. The test–retest period was set to 5 days. The authors agreed that this was an appropriate test–retest period because the participants were not exposed to any intervention between Survey 1 and Survey 2 and had suffered pain for ≥6 weeks.

2.5 Patient-reported outcome measures

2.5.1 Pain self-efficacy questionnaire (PSEQ)

The PSEQ measures the degree of pain self-efficacy [8] and consists of ten items that address the patients’ perceived beliefs in their ability to perform different everyday activities and life situations despite pain. Each item is rated on a seven-point Likert scale from zero (not at all confident) to six (completely confident). The ten items form a unidimensional scale, where zero indicates a low degree of pain self-efficacy and 60 indicates a high degree of pain self-efficacy [8]. The Danish version of the PSEQ has shown good test–retest reliability for patients with LBP for >12 months (ICC = 0.83) [17].

2.5.2 Oswestry disability index (ODI)

The ODI is developed to measure the degree of disability in patients with LBP and consists of ten items reflecting different functions in the patient’s life. Each item is rated on a five-point Likert-scale where zero indicates a high degree of functional level and five indicates a low degree [19]. The Danish version of the ODI has an excellent test–retest reliability (ICC = 0.91) in patients with LBP [20].

2.5.3 Pain intensity (NPRS)

The NPRS is a patient-reported outcome, developed to assess the pain intensity, where patients rate their average of experienced pain during the last 24 h on a Likert scale from zero (no pain) to ten (worst imaginable pain) [21,22].

2.5.4 Tampa scale of kinesiophobia (TSK-11)

The TSK-11 is developed to measure fear of movement/(re)-injury [23]. Each item is rated on a four-point Likert scale ranging from one (strongly disagree with the statement) to four (strongly agree with the statement). The TSK-11 has been translated and culturally adapted to Danish for a group of chronic pain patients (unpublished data) [24], and the test–retest reliability has been found to be good ICC_2,1 = 0.87 [25].

2.6 Statistics

All data were analyzed to assess whether it was normally distributed. Normally distributed continuous data was expressed as the mean and standard deviation (SD), with non-normally distributed data expressed as the median and interquartile range. Categorical and dichotomous data were presented as the frequency and percentage of the total.

2.6.1 Floor or ceiling effects

The PSEQ data from Survey 1 was used to calculate possible floor or ceiling effects. The percentages of patients who scored zero (floor effect) or the maximum of 60 (ceiling effect) were calculated. If more than 15% of the patients scored either zero or 60, the data were interpreted as floor or ceiling effects, respectively [26].

2.6.2 Internal consistency

Data from Survey 1 was used to estimate the internal consistency for the PSEQ. Cronbach’s alpha was calculated for the unidimensional scale that included all ten items. A Cronbach’s alpha correlation of >0.7 was interpreted as acceptable [14,26].

2.6.3 Construct validity

Construct validity was assessed by hypothesis testing to evaluate the convergent validity. Data from Survey 1 was used, and Pearson’s correlation coefficient was used to estimate the correlations. While there is no definitive measure of pain self-efficacy to which the PSEQ can be compared, other constructs were chosen to measure the construct validity, based on previous research [9,27]. A negative moderate to strong correlation between ODI and pain self-efficacy was expected, because according to the self-efficacy theory, patients with low self-efficacy may lack the confidence to perform specific tasks, leading them to avoid everyday activities [8]. A negative moderate to low correlation between the PSEQ and the NPRS was set up based on previous findings [27], and because every item in PSEQ encompasses the pain. A negative moderate to low correlation between PSEQ and TSK-11 was expected, based on previous findings on kinesiophobia [9] and based on the fear avoidance model, which describes that, if the pain is perceived as threatening, it can lead to anxiety and fear of engaging in physical activity [23]. As the patients engage in less physical activity, they may start to feel less capable of managing their pain and performing daily tasks, leading to lower pain self-efficacy.

Construct validity was rated in terms of the percentage agreement of the hypotheses with the results: high, ≥75%; moderate, 50–74%; and low, <50% [26].

2.6.4 Test–retest reliability

Test–retest reliability for the PSEQ was evaluated by calculating the ICC_2.1 with a 95% confidence interval (CI). Test–retest reliability was interpreted according to Koo and Li [28] as follows: poor, <0.5; moderate, ≥0.5 to <0.75; good, ≥0.75 to ≤0.90; and excellent, >0.90.

2.6.5 Measurement error

Measurement error was estimated by calculating the standard error of measurement (SEM), using the formula SEM_agreement = SD × √1 − ICC [29]. Furthermore, the SEM was used to calculate the smallest detectable change (SDC), using the formula SDC₉₅ = 1.96 × √2 × SEM [29].

All statistical analyses were conducted using STATA 17 statistical software (StataCorp, College Station, TX, USA).

3 Results

In total, 141 LBP participants consented to participate in the project. However, 27 participants failed to answer Survey 1; a further three participants were excluded due to a self-reported pain period of less than 6 weeks and two were excluded due to missing values in the PSEQ. Hence, in total, 109 participants were included for analysis of internal consistency and construct validity (see Figure 1).

Figure 1

Flowchart of participants’ inclusion.

Of the 109 participants, 15 participants were excluded from the test–retest study due to the following reasons: failure to answer Survey 2 (n = 8); an unacceptable test–retest period of more than 10 days (n = 4); and missing values in the PSEQ (n = 3). Hence, in total, 94 participants were included in the test–retest study (see Figure 1). On average, there were 4.2 days between recruitment and Survey 1 and 6.5 days between Survey 1 and Survey 2 (test–retest period).

Participants’ characteristics are shown in Table 1. In the sample included for analysis in relation to test–retest reliability, 67% of the participants were women and the mean age was 45.1 (15.9) years. Of the included participants, 42.6% had pain for >2 years.

Table 1

Characteristics of the participants

	Non responders (n = 32)	Included for analysis on construct validity and internal consistency (n = 109)	Included for analysis on test–retest reliability and measurement error (n = 94)
Sex (female)
n (%)	13 (40.62)	72 (66.06)	63 (67.02)
Age, years
Mean (SD)	43.66 (13.78)	44.39 (15.49)	45.14 (15.87)
Pain duration, n (%)
0–6 weeks	3 (9.38)	—	—
7–12 weeks	5 (15.62)	7 (6.42)	5 (5.32)
3–12 months	6 (18.75)	40 (36.70)	35 (37.23)
1–2 years	4 (12.50)	16 (14.68)	14 (14.89)
>2 years	14 (43.75)	46 (42.20)	40 (42.55)
Recidiv of LBP, n (%)
Yes	23 (71.88)	62 (56.88)	54 (57.45)
No	9 (28.12)	47 (43.12)	40 (42.55)
BMI, Kg/m ²
Mean (SD)		25.52 (3.90)	25.66 (4.05)
Education, n (%)
Low education		4 (3.67)	4 (4.25)
Medium education		33 (40.37)	26 (38.3)
High education		54 (49.54)	49 (52.13)
Others		7 (6.42)	5 (5.32)
Work Status, n (%)
Employed		50 (45.87)	43 (45.74)
Student		6 (5.5)	4 (4.26)
Employed with sick report		6 (5.50)	5 (5.32)
Sick report full time		19 (17.43)	14 (14.89)
Social benefit (Unemployed, work ability enhancement program, incapacity benefit)		15 (7.34)	13 (9.57)
Age related pension		12 (11.01)	12 (12.76)
Others		7 (6.42)	7 (7.45)
Comorbidity, n (%)
Osteoarthritis		31 (28.44)	29 (30.85)
Hypertension		13 (11.93)	13 (13.83)
Persistent abdominal pain		4 (3.67)	3 (3.19)
Osteoporosis		6 (5.50)	6 (6.38)
Cardiovascular diseases		3 (2.75)	3 (3.19)
Diabetes		6 (5.50)	6 (6.38)
Atrial fibrillation		6 (5.50)	6 (6.38)
Depression		12 (11.01)	11 (11.70)
Astma		15 (13.76)	15 (15.96)
Others		23 (22.55)	19 (21.59)
Smoker, n (%)
Daily		14 (12.84)	12 (12.77)
Sometimes		8 (7.34)	6. (6.38)
No		87 (79.82)	76 (80.85)

n = number of participants, SD = standard deviation, BMI = body mass index.

The mean sum scores of the PSEQ, ODI, NPRS, and TSK-11 are shown in Table 2.

Table 2

The mean sum score of the following questionnaires: Pain Self-Efficacy Questionnaire, Oswestry Disability Index, Numeric Pain Rating Scale, and Tampa Scale of Kinesiophobia

Sum score	Included for analysis on construct validity and internal consistency	Included for analysis on test-retest reliability and measurement error
Sum score	Survey 1	Survey 1	Survey 2
Pain Self efficacy, PSEQ
Scale (0–60)
mean (SD)	35.75 (13.14) (n = 109)	35.32 (13.04) (n = 94)	35.32 (12.52) (n = 94)
Disability, ODI
Scale (0–50)
mean (SD)	15.85 (7.58) (n = 99)
Pain Intensity, NPRS
Scale (0–10)
mean (SD)	4.80 (1.66) (n = 106)
Kinesiophobia, TSK-11
Scale (11–44)
mean (SD)	27.15 (4.57) (n = 109)

The mean sum score of the following questionnaires: PSEQ = Pain Self-Efficacy Questionnaire, ODI = Oswestry Disability Index, NPRS = Numeric Pain Rating Scale, TSK-11 = Tampa Scale of Kinesiophobia, SD = standard deviation. Survey 1 = the first time the participants reply to the PSEQ. Survey 2 = the second time the participants reply to the PSEQ.

3.1 Interpretability and internal consistency

No floor (0%) or ceiling (0%) effects were found in the PSEQ and the internal consistency was acceptable (r = 0.93; 95% CI = 0.9–0.93).

3.2 Construct validity

Construct validity between the PSEQ and the ODI, NPRS, and TSK-11, respectively, is shown in Table 3. The correlation between the PSEQ and the ODI was found to be strongly negative. This indicates that when a patient has a low degree of disability, it is likely that the patient has a high degree of pain self-efficacy. A moderate negative correlation was found between the PSEQ and the NPRS and between the PSEQ and the TSK-11, indicating that when a patient reports a low degree of pain intensity or has a low degree of kinesiophobia, the patient may have a high degree of pain self-efficacy. The hypotheses were thereby met, and the construct validity was found to be high.

Table 3

Construct validity

	PSEQ
	Hypothesized correlation	Estimated correlation	Hypothesis acceptance (yes or no)
ODI	Moderate-to-high negative correlation (>−0.6)	−0.8235	Yes
NPRS	Moderate-to-low negative correlation (>−0.3)	−0.4524	Yes
TSK-11	Moderate-to-low negative correlation (>−0.3)	−0.5145	Yes

Hypothesized and estimated correlation between Pain Self-Efficacy Questionnaire (PSEQ) and disability measured with Oswestry Disability Index (ODI), Pain Self-Efficacy Questionnaire (PSEQ), and pain intensity measured with Numeric Pain Rating Scale (NPRS) (24 h average pain), Pain Self-Efficacy Questionnaire (PSEQ), and kinesiophobia measured with Tampa Scale of Kinesiophobia (TSK-11).

Bold values are significant of P < 0.001.

3.3 Test–rest reliability

The PSEQ demonstrated good test–retest reliability, with ICC_2.1 = 0.89 (95% CI = 0.82–0.92).

3.4 Measurement error

The SEM_agreement was calculated to be 4.52 and the SDC₉₅ was 12.52 points.

4 Discussion

In summary, this study demonstrates acceptable test–retest reliability and internal consistency of the Danish version of the PSEQ among patients suffering from subacute and chronic LBP, treated in a hospital outpatient clinic. No floor or ceiling effects were observed for the specific sample. Furthermore, high construct validity was found between the PSEQ and ODI, NPRS, and TSK-11 respectively. The test–retest reliability was found to be good, which is in line with the results of a systematic review that included 10 studies and found an overall good test–retest reliability of the PSEQ (weighted mean ICC = 0.86, range = 0.75–0.93) in patients with chronic musculoskeletal pain, including subacute and chronic LBP [28]. Only two studies have investigated the measurement properties of the Danish version of the PSEQ [16,17]. One study investigated a group of chronic LBP patients (n = 92) and found good test–retest reliability of the PSEQ, with an ICC of 0.83 (95% CI = 0.75–0.88) [17]. The other study was conducted in a patient group diagnosed with fibromyalgia (n = 74), again finding good test–retest reliability of the PSEQ, with an ICC of 0.89 (95% CI = 0.83–0.93) [16]. Overall, the interpretation of these results is similar to our findings. Only minor differences in the estimates were observed, possibly due to differences in the included patient group, sample size or the slightly longer test–retest period (14 days) [16]. Additionally, Rasmussen et al. [16] and Vejlgaard et al. [17] did not describe the specific ICC model utilized, which hinders direct comparison and could explain the minor disparities.

The SEM_agreement found in the present study is in line with previous findings reported for the Danish version of the PSEQ, where the SEM was found to be 4.57 and the SDC₉₅ to be 12.67 [17]. In the Italian version, slightly higher SEM_agreement (5.66) and SDC₉₅ (15.96) values were found [9]. In comparison, the English version’s SEM and SDC₉₅ seem to be slightly lower, with SEM = 3.95 and SDC₉₅ = 10.9 [30]. In a Yoruba version of the PSEQ, low SEM (1.2) and SDC₉₅ (3.3) values were reported [31]; however, the methods used for calculation were not described, making the results slightly incomparable and possibly explaining the differences.

In line with previous studies, the internal consistency was found to be excellent [27], which indicates that the Danish PSEQ exhibits a commendable level of internal consistency.

A strong negative correlation between the PSEQ and disability measured by the ODI was found in the present study. Two previous studies have investigated the construct validity between PSEQ and disability in LBP patients, where slightly lower correlation coefficients were observed [9,32]. However, both studies used the Roland–Morris Disability Questionnaire as a disability outcome and are therefore not completely comparable with the present study. An additional factor contributing to variation in the correlation coefficients could be differences between patient groups across the present study and the two previous studies. In the studies by Chiarotto et al. [9] and Yang et al. [32], patients with specific LBP diagnoses were excluded. Furthermore, there are differences in the level of disability, as participants in the current study are less disabled compared to the two other studies [9,32]. Additionally, differences in the duration of LBP and variation in the environmental setting could further contribute to the observed differences. One possible explanation of the observed strong correlation between the ODI and the PSEQ is that patients with low self-efficacy may not have the confidence to perform everyday tasks, which might result in avoiding everyday activities. Consequently, these patients might gradually become increasingly inactive and disabled over time. Conversely, patients with high self-efficacy are likely to continue engaging in activities and therefore might not become increasingly disabled [8].

A moderate negative correlation was found between the NPRS and the PSEQ. These findings are consistent with previous findings [9]. However, in the Chinese version of the PSEQ presented in a validation study by Yang et al. [32], the correlation between the PSEQ and pain intensity was found to be lower, with a correlation coefficient of r = −0.29. Yang et al. used the Brief Pain Inventory to measure pain intensity [32] and, therefore, the results are not completely comparable with the present study, which might explain the differences. In the PSEQ, patients are explicitly instructed to indicate their confidence in performing a range of activities and tasks despite pain. Therefore, it was expected that there would be a negative correlation between the PSEQ and the pain intensity, as the pain is taken into account throughout the PSEQ. However, pain self-efficacy is a psychological construct, comprised of the patient’s beliefs and self-control regarding pain and not a measure of perceived pain intensity. Therefore, in line with our a priori hypothesis, a stronger correlation between the PSEQ and the NPRS was not expected. In the present study, we found a moderate negative correlation between the PSEQ and the TSK-11. This is consistent with previous findings [9]. Kinesiophobia is defined as the most extreme form of fear of movement [23], whereas pain self-efficacy is defined as the patient’s perceived confidence in performing specific tasks despite pain. Hence, we a priory expected a moderate negative correlation between these two constructs, because we expected that patients with high kinesiophobia would experience less confidence in performing everyday tasks. In a previous study, it has been suggested that there are overlaps between the two psychological constructs, kinesiophobia, and pain self-efficacy [33]. Our findings suggest that the two constructs are related, but they remain two distinct constructs. Previous research also found that pain self-efficacy mediates the relationship between pain and disability more than kinesiophobia does. Pain self-efficacy might be a more significant factor than kinesiophobia in understanding the relationship between pain and disability [34].

When investigating reliability, it is crucial that the patients are stable between the two tests on the construct to be measured [35]. To reduce the risk of a possible effect on pain self-efficacy from the hospital visit, participants received the first assessment 2 days after their appointment. This was considered an appropriate timeframe to “wash out” the experiences from the hospital.

The test–retest period was set to 5 days to minimize the potential risk that the participants could be in contact with other health professionals who could possibly affect the participants’ pain self-efficacy. At the same time, the test–retest period should not be too short to prevent recall bias. Nonetheless, many of the patients answered Survey 1 more than 2 days after their first appointment (on average, 4.2 days after). This subsequently resulted in Survey 2 being completed an average of 9.2 days after the assessment at the hospital rather than the planned 7 days. Due to the prolonged time period, contacts with the healthcare, that could possibly have influenced the participant’s pain self-efficacy, cannot be ruled out. Therefore, to minimize this risk, we excluded patients with a test–retest period of >10 days. Initially, we discussed developing a Global Rating Scale for pain self-efficacy to check for the stability between Survey 1 and Survey 2. However, as concluded by others [17], this was not feasible because no golden standard for pain self-efficacy exists; thus, we concluded that it was not possible to formulate one item containing the entire construct of pain self-efficacy.

Out of the 141 participants who consented to participate in our study, 27 did not answer Survey 1. Interestingly, the non-responders were predominantly males; therefore, the sample that responded may not accurately reflect all patients who receive a referral to an outpatient clinic. However, other studies have shown that the prevalence and incidence of LBP are higher among females [1]. From that perspective, the included group is similar to the population group. Furthermore, among the non-responders, 15% reported that they had subacute LBP, whereas in the included group, this percentage was only about 5%. A possible reason for this difference could be that patients with subacute LBP might be less affected by their pain and therefore less interested in participating in research.

4.1 Strengths and limitations

The fact that patients have been recruited from two different locations is regarded as a strength of this study, indicating that it is highly likely that our results may be applicable to other hospitals in Denmark. Furthermore, only five patients (4.5%) were excluded from the analysis because of missing items in the PSEQ, which is below the acceptable upper limit of 15% [15].

Another notable strength is that it was possible to make phone calls in cases where patients did not respond to Survey 2. Without this capability, the dropout from Survey 1 to Survey 2 could have been substantially higher. It is also seen as a methodical strength that both Survey 1 and Survey 2 were completed in the same settings.

A limitation of the present study is that we cannot prove that all patients were stable over the entire test period, and hence we could only assume this according to the methodical precautions that have been taken. Furthermore, the minimal clinically important difference has not been investigated in the present study and remains unknown. Another limitation is that the sample size was not considered adequate to evaluate structural validity and hence the unidimensionality of the Danish PSEQ remains unknown.

4.2 Implications

The initial evaluation of the measurement properties of the PSEQ reported in the present study in a sample of subacute and chronic LBP patients shows promising results. Thus, the PSEQ can now be considered for use in clinical practice and in further research in Danish settings. However, additional evaluation of the measurement properties of the PSEQ is still needed.

In our study, we conclude that if a patient changes more than 13 points on the PSEQ scale we can be 95% sure that the change is due to a real change in pain self-efficacy. Since the range of the scale is 0–60 points, it might be argued that an SDC₉₅ of 13 points is a large value, and this should be taken into account when the PSEQ is utilized as an outcome measurement in a treatment session. Knowing the SDC₉₅ value in clinical practice is highly relevant, particularly when the instrument is utilized as an outcome measurement (to monitor treatment effect). What constitutes a meaningful change for the patients is still unknown; therefore, further studies to evaluate the responsiveness and the minimal clinically important difference are necessary.

In conclusion, the Danish version of the PSEQ demonstrated high construct validity with ODI, NPRS, and TSK-11. Furthermore, it exhibited acceptable internal consistency, good test–retest reliability, and an SDC₉₅ of 12.52 points. These findings indicate that the Danish version of the PSEQ is suitable for use among subacute and chronic LBP patients in outpatient clinics.

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Acknowledgments

We want to thank all the physiotherapists in the back pain clinics at Copenhagen University Hospital – Rigshospitalet and Bisbebjerg and Frederiksberg Hospital, for including patients and collecting data.

Research ethics: The research involving human subjects complied with all the relevant national regulations and institutional policies and is in accordance with the tenets of the Helsinki Declaration. According to Danish legislation and the Act on Biomedical Research Ethics Committee System in Denmark, research using questionnaires does not require approval from an ethics committee. The study was approved by the Danish Data Protection Agency (P-2020-1157).
Informed consent: Informed consent has been obtained from alls individuals included in this study.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Research funding: None declared.
Data availability: The raw data can be obtained on request from the corresponding author.
Artificial intelligence/Machine learning tools: Not applicable.

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Received: 2024-04-11

Revised: 2024-08-22

Accepted: 2024-08-29

Published Online: 2024-10-04

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/sjpain-2024-0032

Keywords for this article

pain self-efficacy; low back pain; measurement properties; reliability; validity

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