KHYBER MEDICAL UNIVERSITY, PESHAWAR Pharmacokinetic profile of Carbamazepine and valproic acid therapy in management of epilepsies with reference to single nucleotide polymorphisms in EPHX1, SCN1A and SCN2A genes in population of Khyber Pakhtunkhwa Principal Investigator: Dr. Niaz Ali
Validity of four pain intensity rating scalesPAINÒ 152 (2011) 2399–2404 Validity of four pain intensity rating scales Maria Alexandra Ferreira-Valente , José Luís Pais-Ribeiro , Mark P. Jensen a Faculdade de Psicologia e Ciências da Educação da Universidade do Porto, Porto, Portugalb Portuguese Foundation for Science and Technology, Lisbon, Portugalc Unidade de Investigação em Psicologia e Saúde (Psychology and Health Unit), Lisbon, Portugald Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, WA, USA Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
The Visual Analogue Scale (VAS), Numerical Rating Scale (NRS), Verbal Rating Scale (VRS), and the Faces Received 22 February 2011 Pain Scale-Revised (FPS-R) are among the most commonly used measures of pain intensity in clinical and Received in revised form 25 June 2011 research settings. Although evidence supports their validity as measures of pain intensity, few studies Accepted 11 July 2011 have compared them with respect to the critical validity criteria of responsivity, and no experimenthas directly compared all 4 measures in the same study. The current study compared the relative validityof VAS, NRS, VRS, and FPS-R for detecting differences in painful stimulus intensity and differences between men and women in response to experimentally induced pain. One hundred twenty-seven sub- jects underwent four 20-second cold pressor trials with temperature order counterbalanced across 1°C, ValidityNumerical Rating Scale 3°C, 5°C, and 7°C and rated pain intensity using all 4 scales. Results showed statistically signiﬁcant dif- Visual Analogue Scale ferences in pain intensity between temperatures for each scale, with lower temperatures resulting in higher pain intensity. The order of responsivity was as follows: NRS, VAS, VRS, and FPS-R. However, there Verbal Rating Scale were relatively small differences in the responsivity between scales. A statistically signiﬁcant sex maineffect was also found for the NRS, VRS, and FPS-R. The ﬁndings are consistent with previous studies sup-porting the validity of each scale. The most support emerged for the NRS as being both (1) most respon-sive and (2) able to detect sex differences in pain intensity. The results also provide support for thevalidity of the scales for use in Portuguese samples.
Ó 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
ﬁndings suggest that no single measure is consistently moreresponsive than any of the other measures , The Visual Analogue Scale (VAS), Numerical Rating Scale (NRS), although the responsivity of the VAS, NRS, VRS, and FPS-R has Verbal Rating Scale (VRS), and Faces Pain Scale-Revised (FPS-R) are yet to be directly compared in the same study. Also, the validity among the most common measures of pain intensity used by of these scales has never been examined in a sample of individuals clinicians and researchers. Evidence supports the reliability and from Portugal. Evaluations of common pain measures in samples validity of each of these measures across many populations from different countries and cultures can help establish the . However, each measure has strengths and weaknesses.
cross-cultural generalizability of validity ﬁndings.
For example, research indicates that VASs have more ratio scale Perhaps the most important validity criterion for a pain measure qualities than other pain intensity scales for groups of patients is its ability to detect changes in pain with pain treatment or proce- (but not necessarily for individuals) , although some dures known to produce pain. One method for doing this would be to authors note that VASs scales do not always have linear qualities use an experimental design in which the amount of stimulation is and are not always normally distributed Pain scales with highly controlled The cold-pressor test is an experimental more response levels (eg, the VAS or 0–10 NRS relative to the 6- method for inducing pain that is thought to reﬂect many (but not point FPS-R or 4-point VRS) have the potential to be more sensitive all) of the critical components of clinical pain , and its advantages although more response categories do not necessarily are discussed in the literature . Moreover, an increase translate to more responsivity Furthermore, research in pain intensity as water temperature decreases is well docu-mented, with small variations in water temperature resulting in sig-niﬁcant differences in pain intensity ⇑ Corresponding author. Address: Rua 25 de Abril, n° 5, Idanha – Belas, Belas A number of studies have examined the inﬂuence of sex on pain 2605-119, Portugal. Tel.: +351 969082988.
perceptions and pain response to experimental pain with E-mail address: (M.A. Ferreira-Valente).
0304-3959/$36.00 Ó 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
M.A. Ferreira-Valente et al. / PAINÒ 152 (2011) 2399–2404 normally menstruating women usually being more sensitive topainful stimuli than men . Laboratory pain experi-ments that include both men and women provide an opportunityto compare the ability of pain ratings to detect these well-estab-lished sex differences.
The primary aim of the current study was to compare the relative validity of VAS, NRS, VRS, and FPS-R for detecting differences in pain-ful stimulation and for detecting sex effects in response to painfulstimulation. Based on previous research, we hypothesized that all4 scales would be able to detect a sex effect and differences in painresulting from 4 temperatures (1°C, 3°C, 5°C, and 7°C). Given the lar-ger number of response levels of the VAS and NRS, we also antici-pated that these would evidence greater responsivity than the VRSor FPS-R. Finally, this study also sought to evaluate the validity ofthe pain intensity rating scales in a Portuguese sample.
Fig. 1. The Numerical Rating Scale, Visual Analogue Scale, Faces Pain Scale – 2.1. Participants Revised, and Verbal Rating Scale; Faces Pain Scale – Revised, copyright Ó2001,International Association for the Study of Pain, reproduced with permission, Participants were 127 volunteer university students. Exclusion criteria included: (1) being under 18 years of age; (2) reporting a his-tory of any of the following diagnoses or medical problems: muscu- with the end points ‘‘No pain'' and ‘‘Worst imaginable pain'' placed loskeletal problems, cancer, heart disease, stroke, epilepsy, diabetes at each end of the line. Respondents are asked to make a mark on or Raynaud syndrome; (3) having an open wound, cut, or fracture in the line that best represents the level of pain intensity that they are any of the upper limbs; (4) having a cognitive or physical disability experiencing. The NRS is an 11-point scale consisting of integers that could prevent participation; or (5) refusal to participate.
from 0 through 10; 0 representing ‘‘No pain'' and 10 representing Of the 127 subjects who expressed an interest in participating in ‘‘Worst imaginable pain.'' Respondents select the single number the study, 112 were eligible and completed the entire experimental that best represents their pain intensity. Although validity studies procedures. Of the 112 completers, 3 subjects were excluded from for the Portuguese versions of these measures have not been pub- the analyses because they were unable to understand how to use lished, to our knowledge, both the VAS and the NRS used in this the VAS. Thus, complete data were available for 109 subjects, 56 of study have been previously used in research with Portuguese sam- whom were female (51.4%). The ages of the participants ranged from ples , and are recommended for use by the Portuguese 18 to 40 years old (M = 22.27, SD = 3.92; Female: M = 21.24, Ministry of Health (Normative Circular n° 9/DGCG of June 14, SD = 3.45; Male: M = 23.34, SD = 4.13). Most of the sample had their 2003). The VRS is a 5-point scale consisting of a list of phrases permanent residence in an urban area (74.3%), and the remainder (no pain, mild pain, moderate pain, intense pain, maximum pain) (25.7%) lived in a rural area. Ninety-nine participants were under- that describe increasing levels of pain intensity. Respondents select graduate college students (33.0%, 17.4%, 21.1%, 11.0%, and 8.3% in the single phrase that best characterizes their pain intensity. The their ﬁrst, second, third, fourth, and ﬁfth year, respectively). Ten VRS used in this study is commonly used by Portuguese research- (9.2%) of the participants were in graduate school.
ers (eg, The FPS-R is a 6-point scale, with 6 differentfaces that represent increasing levels of pain intensity. Respon- dents are asked to select the one expression that best characterizeshis or her pain intensity, from the left-most face (‘‘No pain''), to the The cold-pressor apparatus used consisted of 4 thermal insu- right-most face (‘‘Very much pain''). Each illustration corresponds lated containers with 18.1 L of capacity containing water chilled to a numeric score (0, 2, 4, 6, 8, or 10). Research supports the valid- to 4 different temperatures. The apparatus was capable of main- ity of each of the pain measures used in this study as measures of taining water temperatures within ±0.5°C of the desired tempera- pain intensity . Although the FPS-R was ini- tures throughout the experimental procedures. Each container tially developed for use with children, researchers also use the had 2 compartments separated by a metal ﬁlter, one of which held measure in samples of individuals with cognitive and communica- water, ice, and a water pump, and the other (the immersion tank) tion impairment. The Portuguese (Portugal) translation of the FPS- contained water alone with an armrest; the participants' hands R was performed by Batalha and is available online therefore never came in direct contact with the ice. Four water pumps (JAD, model SP-602, 200 L/h, Guangdong, China) made thewater ﬂow continuously between the 2 compartments of each con- tainer to prevent warm water pockets from forming near the partic-ipants' hands The temperature of the hand and water was The cold-pressor procedures closely followed the guidelines for monitored and controlled by asking the participants to hold a mer- this task described in the literature, and were adapted to ﬁt the cury thermometer in the palm of their hands and immersing a ther- study aims The study had Institutional Review Board mometer in the water, respectively. One extra thermal insulated approval. The study procedures were described to all potential par- container without divisions contained an armrest and tepid water.
ticipants and each was given a written consent form to read andsign before any measures were administered. After signing the consent form, participants completed a demographic and medicalhistory questionnaire in order to identify potential medical condi- presents all the pain intensity rating scales used in this tions that would prevent participation. Participants who met any study. The VAS consists of a horizontal line 100 mm in length, of the exclusion criteria were then excluded from participation.
M.A. Ferreira-Valente et al. / PAINÒ 152 (2011) 2399–2404 The nondominant hand temperature was measured in all par- Pain ratings, as measured by VAS, NRS, VRS, and FPS-R, showed ticipants, followed by hand washing to the wrist. The nondominant normal distributions for each of the 4 temperatures (Sk <1 and Ku hand was then immersed to the wrist in the container with tepid <1). However, for each measure, we noted a violation of the water (36°C ± 1°C) for 2 minutes, in order to reduce preexisting dif- ferences in hand temperature Hand temperature was again p < 0.001; NRS: W = 0.59, X2 (5) = 55.53, p < 0.001; VRS: W = 0.82, measured, and participants were instructed to immerse the hand X2 (5) = 20.54, p < 0.01; FPS-R: W = 0.81, X2 (5) = 21.74, p < 0.01].
to the wrist in the ﬁrst cold water container for 20 seconds. Partic- We therefore used Huynh-Feldt epsilon to determine the degrees ipants were also told they could take the hand from the cold water of freedom in the analyses .
at any moment if it felt too uncomfortable to continue. For each of As hypothesized, there were statistically signiﬁcant tempera- the 4 study conditions, only 3 participants took their hands out ture main effects for each of the 4 scales used in the study [VAS: of the water before the established tolerance time (20 seconds).
FHuynh-Feldt(2.48, 265.24) = 85.74; p < 0.001, g2 = 0.45; p = 1; NRS: After the 20-second cold immersion, when we anticipated that FHuynh-Feldt(2.28, 243.64) = 93.49; p < 0.001, g2 = 0.47; p = 1; VRS: pain would be at its most intense, we administered paper-and- g2 = 0.42; p = 1; pencil versions of the 4 pain measures (VAS, NRS, VRS, and FPS- FHuynh-Feldt(2.70, 286.42) = 72.62; p < 0.001, g2 = 0.32; R). The measures were presented in a random order using a Latin p = 1]. Moreover, all of the effect sizes associated with the temper- Square design. After a 3-minute break, the participants were asked ature main effects in the omnibus ANOVAs for each measure were to immerse his or her hand into the tepid warm water again for large. Effect sizes for the comparisons for each pair of temperature 2 minutes, and hand temperature was again assessed. Participants differences ranged from medium (0.17) to large (0.59), consistent underwent 4 trials with 4 different water temperatures (1°C, 3°C, with the differences between temperatures. These differences also 5°C, and 7°C), in counterbalanced order, as proposed by Mitchell follow the same pattern for each scale (and ).
and colleagues Each participant experienced each water tem- Statistically signiﬁcant sex main effects emerged for the NRS perature only once, and provided ratings using each of the 4 scales [F(1, 107) = 4.40; p < 0.05, g2 = 0.04; p = 0.55], VRS [F(1, 107) = for each temperature; thus, each participant provided 16 ratings.
8.38; p < 0.01, g2 = 0.07; p = 0.82], and FPS-R [F(1, 107) = 14.13; Participants were not given any information regarding the water p < 0.001, g2 = 0.12; p = 0.96], and a nonsigniﬁcant trend emerged temperature in each container.
for the main effect of gender on pain ratings on VAS[F(1, 107) = 3.49; p = 0.07, g2 = 0.03; p = 0.46], with women report- 2.4.1. Data analysis ing higher pain ratings in every experimental condition.
We ﬁrst computed medians, means, and SDs for demographic Post hoc Fisher's least signiﬁcant difference paired tempera- and study variables for descriptive purposes. We next computed tures comparisons for each pain scale found statistically signiﬁcant Pearson correlations between the VAS, NRS, FPS-R, and VRS, for differences between all observations (p < 0.001). As would be ex- descriptive purposes. In order to compare the ability of VAS, NRS, pected, in every case, lower temperatures resulted in higher pain FPS-R, and VRS to detect differences in pain stimuli resulting from intensity ratings for all 4 scales.
4 different temperatures, as well as the hypothesized sex main ef- The NRS and VAS evidenced slightly higher effect sizes (0.47 fect on pain intensity ratings, we then performed 4 mixed-design and 0.44, respectively) and higher F statistics (93.49 and 85.74, repeated-measures analyses of variance (ANOVAs), with the pain respectively) than VRS (0.42 effect size and F statistic of 76.36) intensity ratings as the dependent variables, and sex and temper- and FPS-R (0.32 effect size and F statistic of 72.62). Power analyses ature as the independent variables. Prior to these analyses, we based on these effect sizes indicated that the number of partici- evaluated test assumptions, namely normality and sphericity of pants needed to be able to detect an overall difference between the variance–covariance matrix, by analysing skewness (Sk) and temperatures, as tested by an ANOVA, would be 5, 5, 5, and 7 for kurtosis (Ku), with values of Sk and Ku lower than 1 indicating ab- the NRS, VAS, VRS, and FPS-R, respectively. Power analyses to sence of severe violation of normality assumption and Mauchlytest, respectively . If a violation of the assumption of spheric-ity was found, we planned to use Huynh-Feldt epsilon to set the Table 1Means and SDs of the pain ratings for each temperature condition.
degrees of freedom In the event that a signiﬁcant tempera-ture effect was found, we planned to perform between-tempera- ture comparisons using post hoc Fisher's least signiﬁcant difference tests. Effect sizes were estimated using g2, and, along with P values and F statistic magnitudes, were used to compare the hypothesized differences in responsivity of the 4 pain mea- sures, with larger g2 and F statistics, as well as smaller P values, indicating greater sensitivity Finally, we performed power analyses to determine the sample size required to obtain signiﬁcant effects for each of the 4 measures, both for the omnibus ANOVA and for each planned temperature paired comparison. Al- pha was set at 0.05 and power at 0.95 for these analyses. Statistical analyses were computed using software PASW Statistics 18 (v. 18, SPSS Inc. Chicago, IL, USA) and G⁄Power (v. 3.1) .
lists the descriptive statistics of the study variables, and presents the correlation coefﬁcients between the pain mea- sures. As can be seen, the pain scales showed strong to very strong and statistically signiﬁcant inter-scale correlations (rs ranging VAS, Visual Analogue Scale; NRS, Numerical Rating Scale; FPS-R, Faces Pain Scale- from 0.79 to 0.96) for all 4 water temperatures.
Revised; VRS, Verbal Rating Scale.
M.A. Ferreira-Valente et al. / PAINÒ 152 (2011) 2399–2404 Table 2Inter-scale correlation coefﬁcients between the VAS, NRS, FPS-R, and VRS.
VAS, Visual Analogue Scale; NRS, Numerical Rating Scale; FPS-R, Faces Pain Scale-Revised; VRS, Verbal Rating Scale.
Table 3Effect sizes (and number of participants required to obtain signiﬁcant effects) for the VAS, NRS, FPS-R, and VRS.
VAS, Visual Analogue Scale; NRS, Numerical Rating Scale; FPS-R, Faces Pain Scale-Revised; VRS, Verbal Rating Scale.
Fig. 2. Average pain intensity ratings across temperatures. Error bars represent SD.
compute the number of participants needed to detect differences and FPS-R. This is consistent with previous studies demonstrating between each pair of temperatures for each of the pain scales are the superiority of VAS and NRS responsiveness, due perhaps to the presented in , and range from 5 to 19. These are consistent larger number of response levels that these 2 scales provide with the distance between temperatures, with larger distances In our study, the NRS has shown to be slightly more (and effect sizes) corresponding to fewer participants needed.
responsive than the VAS, as indicated by its larger effect size and Fstatistic value. This is consistent with a group of studies showing a similar sensitivity between the NRS and VAS or a slight superiorityof the NRS over the VAS . Nevertheless, the results of The results of this study provide strong support for the validity power analyses to determine the number of subjects needed to de- of all 4 scales studied for detecting changes in pain intensity in Por- tect a signiﬁcant effect indicate that the 4 measures have very sim- tuguese university students. All of the scales were able to detect ilar levels of responsivity, with very small differences between differences in pain resulting from 4 different temperatures, with scales in the numbers of subjects needed to detect differences. This variations in temperature resulting in statistically signiﬁcant dif- ﬁnding is consistent with the strong to very strong associations we ferences in pain intensity ratings, and lower temperatures result- found among the study measures (a ﬁnding also consistent with ing in higher pain ratings for each of the 4 scales studied. These previous research, eg, indicating that all 4 measures results are consistent with previous studies that support each tap into the same overall dimension (ie, pain intensity).
scale's validity and show that small variations Thus, the results indicate that all else being equal, any of the 4 in water temperature result in signiﬁcant differences in pain inten- scales could be used for detecting changes in pain, although the sity ratings .
NRS and VAS might be considered ﬁrst when particularly sensitive As predicted, we found some differences in the relative respon- and responsive measures of pain intensity are needed. Based on sivity, with NRS being the most responsive, followed by VAS, VRS, other considerations, however, researchers and clinicians may M.A. Ferreira-Valente et al. / PAINÒ 152 (2011) 2399–2404 elect to choose the NRS over the VAS in many settings. First, the pain is not associated with any tissue damage, whereas pa- although the NRS has not consistently been shown to have ratio tients with clinical pain cannot always be so sure of this. For these properties its scores can provide data for parametric anal- reasons, clinical pain has an emotional signiﬁcance and quality-of- ysis . Also, the NRS has been shown to be at least as life implications that may inﬂuence pain perception There- sensitive as the VAS, whether a 0–10 NRS or a 0–100 NRS is used fore, the study ﬁndings do not necessarily generalize to patients . Third, the NRS is preferred over the VAS by patients with clinical pain conditions. It would be useful to examine the rel- and clinicians for its relative simplicity and ease of administration ative responsivity of the 4 pain measures in response to treatments or procedures known to impact clinical pain conditions to help Fourth, the VAS tends to have higher failure rates determine their generalizability.
than the NRS or VRS, probably because both the NRS and the VRS Nevertheless, the ﬁndings provide support for the validity and sensitivity of all 4 pain scales studied, with the exception that it . This latter point was also supported in the might be best to avoid the use of VAS in studies seeking to examine current study, given our ﬁnding that the only participants excluded sex effects. The ﬁndings also suggest that the NRS may be (very) from the sample for not being able to understand the measures slightly more sensitive than the other measures in our sample of were excluded because they were unable to understand the VAS.
individuals from Portugal; a ﬁnding consistent with some other The VRS is a categorical measure that might not have ratio prop- studies that have compared the NRS to other pain measures, and erties As a result, VRSs do not necessarily have equal intervals supporting their cross-cultural reliability. Research is needed to between levels, which limits the conclusions that can be drawn compare these measures in clinical settings to conﬁrm the general- about the magnitude of differences over time or between patient izability of the current ﬁndings to clinical populations.
groups Also, when differences in responsivity are found,VRSs, as well as the FPS-R, tend to be less sensitive than VAS and Conﬂict of interest statement NRS, consistent with the results from our study. This lower levelof responsivity may be related to the lower number of response None of the authors have any conﬂicts of interest with respect categories of these measures. However, we did ﬁnd that both of to this study.
these scales were able to detect changes in pain associated withdifferences in water temperature, indicating that they are valid and could be used when responsivity is not a critical issue. Also, statisticians note that it is possible to draw va- The authors gratefully acknowledge José Elísio Pereira for his lid conclusions using parametric analysis with ordinal data, such as contribution in the construction of the apparatus, and to Rita Ferre- data from VRSs, especially if number of categories in the scale is 5 ira and Vera Melo for their assistance in data collection. M. Alexan- or more Thus, the VRS can be considered a viable choice dra Ferreira-Valente received PhD grant SFRH/BD/40956/2007 in in settings with patients or research subjects who might be less the past year from the Portuguese Foundation for Science and able to use the NRS (eg, very young individuals or individuals with Technology. José L. Pais Ribeiro received a sabbatical grant from signiﬁcant cognitive impairment). Likewise, our ﬁndings provide FCT (SFRH/BSAB/982/2010) between January and April 2010. Mark support for the validity of the FPS-R in adults, supporting its use P. Jensen received research support, consulting fees, or honoraria in in clinical and research settings. Although the FPS-R has been the past year from Analgesic Research, Consultants in Behavioral developed for use with children and proven useful with people Research, Endo, Fralex, Medtronic, Merck, Pﬁzer, Smith & Nephew, with cognitive and communication disabilities, there may be situ- US Department of Education, US Department of Veterans Affairs, ations or settings in which it might be useful for other populations.
and the US National Institutes of Health.
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