Items (questionnaire questions) for the RCPQ were carefully generated using consensus statements regarding findings from treatment outcome studies of patients with chronic pain or after surgery, literature review of the books, and published articles about chronification of the pain. This process is in line with the recommendations by Cronbach and Meehl that advised researchers to articulate the theoretical concept of an instrument before developing and testing it empirically [17]. We intended to adapt the concept of overinclusiveness, so we did not significantly restrict the number of items to be included in a final version. In total, 27 items were generated, focused on depressiveness, anxiousness, somatic symptoms of anxiety, genital difficulties, pain symptoms, repeated negative medical outcomes, and heartburn. All proposed items were thoroughly discussed with a group of experts possessing multi-professional expertise in acute and chronic pain treatments, psychology, anesthesia, and psychiatry, among others. The proposed version of the questionnaire was tested in cognitive interviews. The instrument was composed of two separate parts: (1) The statements of each item (e.g., “Have you ever experienced any severe pain?”), (2) “If yes, how much was it uncomfortable for you? (0—Not at all, 1—Slightly, 2—Moderately, 3—Very, 4—Extremely)”. Those who did not have experiences listed in the statements left the answer unresponded. We decided to exclude the possibility of answering “no” to make the process of filling out the instrument easier and faster for older patients, who are more frequent in ambulances for pain treatment where we were gathering data. Those who did not experience statements described in the items did not have to answer. Moreover, items 2, 21, and 27 had very specific but similar expressions for the second part of each item (for example: “If yes, how much did your perception of the new pain get worse?”).

The data were collected from September 2022 to October 2023. Respondents were invited to participate in the research during their first visit of the chronic pain out-patient clinic for pain treatment. The patients were informed about the research and had to fill out The Risk of Pain Chronification Questionnaire (RPCQ) and the short form of The Brief Pain Inventory (BPI-SF) while waiting for a medical doctor and the pain treatment. The process of filling out the questionnaires did not significantly prolong the time for receiving a standard treatment. Immediately after the first visit and completing the RPCQ and BPI-SF, respondents were asked to visit an ambulance in half a year for the second time to fill BPI-SF again to see if the treatment had effect. The criteria for participation included (a) age over 18 years and (b) having experienced pain. The patients were not paid for participation.

We obtained data from 230 respondents. Out of this number, only 207 respondents finished the whole RPCQ and were suitable for an exploratory factor analysis. At the start of performing the regression analysis, applying student t tests and repeated analysis of variance, we excluded 114 respondents from those analyses because they did not finish at least 75% of the items for each individual evaluation factor defined as a subgroup of items specific for corresponding factor. Descriptives of the samples are presented in the results of each analyses.

The Brief Pain Inventory (BPI-SF) contains 9 items that are self-administered and used to evaluate the severity of the patient’s pain and the impact of this pain on the patient’s daily functioning. The patient is asked to rate their worst, least, average, and current pain intensity; list current treatments and their perceived effectiveness; and rate the degree that pain interferes with walking ability, work, mood, relations with other persons, enjoyment of life, sleep, and general activity, on a ten-points scale. Inventory was translated and adapted to numerous languages including Chinese, Italian, German, Greek, Norwegian, Japanese, Spanish, and Slovak [18]. According to some authors, BPI-SF can be considered as a reliable instrument. Moreover, some studies already tested construct validity of the BPI-SF by confirmatory factor analysis. In the literature, there were proposed two factor solutions. The first solution operated with three factors named as pain intensity, activity interference, and affective interference; meanwhile, the second solution considered affective interference as an independent factor from the previous two. Atkinson et al. support the conclusion that both solutions are usable for HIV/AIDS and cancer populations [19]. Moreover, Lapane et al. and Tan et al. reported that the second solution has greater validity for patients with non-cancer pain [18, 20]. We decided to use the Slovak version of BPI-SF and its two-factor solution in our study. The first factor is called pain severity. This first factor measures the experiencing of different forms of pain. The second factor is called interference, and its items measure how much pain interferes with daily function of the patients. We decided to call the second factor in our study “a functional ability.”

All analyses were conducted using JASP software version 0.18.1.0. (https://jasp-stats.org/). In the first step, we performed exploratory factor analysis (EFA) with principal axis factoring to determine the validity and factor structure of the instrument. This kind of factor analysis is suitable for assessing theoretical interesting latent constructs rather than to test specific hypotheses. For an EFA, it is appropriate to operate with interval or at least quasi-interval data, which can be assumed for data that we collected. For extracting the number of factors, we implemented oblimin rotation. According to Browne, an oblique rotation permits factors to be correlated, which orthogonal rotation does not, and is thus more representative for data where it is reasonable to assume that different factors in the same instrument in fact correlate to some degree [21]. Also, we performed the Kaiser-Meyer Olkin (KMO) measure of sampling adequacy and the Bartlett’s Test of Sphericity, which indicates if the correlations between items are significantly different from zero, as well as the determinant, checking for a reasonable level of correlation. The scree test was performed to visually inspect the number of factors that precedes the last major drop in eigenvalues. Parallel analysis was implemented in JASP to compare the obtained factor solution with one derived from data that is produced at random with the same number of cases and variables. The final number of factors was decided based on parallel analysis, scree plot, and Kaiser’s rule, as well as the interpretability of the factor solution.

In the second step, we computed the mean subscale scores for the two BPI-SF subscales—severity of the pain (computed items 3, 4, 5, and 6) and functional ability (computed items 10, 11, 12, 13, 14, 15, and 16) and mean subscale scores for four factors of our RPCQ (severe pain and sensitization, visceral somatization, health-related anxiousness, and health-related depressiveness). Into analyses, we included only respondents who answered at least 75% of items for each scale. We estimated the multiple linear regression model and used age and four RPCQ factors as predictors for severity of the pain severity and functional ability of the patients after 6 months of standard treatment. Multiple linear regressions (Enter method) were used to identify the significant predictors. Standardized regression coefficients were obtained using the JASP (soft. version 0.18.1.0). Multicollinearity was controlled by means of tolerance (TOL < 0.10) and variance inflation factor (VIF > 10). On the basis of these criteria, none of the analyzed variables showed multicollinearity.

In the third step, we performed two student t tests of two paired samples and several repeated measures of variance. In the first place, we performed two student t tests to verify if there was a statistically significant difference between pre-test and post-test after 6 six months of standard care for two subscales of BPI-SF: pain severity and functional ability. After that, we performed several repeated analyses of variance to check if there is a statistically significant difference in scores of pain severity and functional ability between pre-test and post-test (after 6 months of standard treatment) according to higher or lower overall score of RPCQ and its factors (2 × 2 repeated measures). These two samples were defined from the overall score of RPCQ and its factors (22 items proposed by EFA). The first sample consisted of respondents who scored ≥ 25th percentile of overall RPCQ score or its four factors, while the second sample consisted of respondents who scored ≤ 75th percentile of overall RPCQ score or its four factors.