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Salis Z, Gallego B, Sainsbury A. Researchers in rheumatology should avoid categorization of continuous predictor variables. BMC Med Res Methodol 2023; 23:104. [PMID: 37101144 PMCID: PMC10134601 DOI: 10.1186/s12874-023-01926-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Accepted: 04/18/2023] [Indexed: 04/28/2023] Open
Abstract
BACKGROUND Rheumatology researchers often categorize continuous predictor variables. We aimed to show how this practice may alter results from observational studies in rheumatology. METHODS We conducted and compared the results of two analyses of the association between our predictor variable (percentage change in body mass index [BMI] from baseline to four years) and two outcome variable domains of structure and pain in knee and hip osteoarthritis. These two outcome variable domains covered 26 different outcomes for knee and hip combined. In the first analysis (categorical analysis), percentage change in BMI was categorized as ≥ 5% decrease in BMI, < 5% change in BMI, and ≥ 5% increase in BMI, while in the second analysis (continuous analysis), it was left as a continuous variable. In both analyses (categorical and continuous), we used generalized estimating equations with a logistic link function to investigate the association between the percentage change in BMI and the outcomes. RESULTS For eight of the 26 investigated outcomes (31%), the results from the categorical analyses were different from the results from the continuous analyses. These differences were of three types: 1) for six of these eight outcomes, while the continuous analyses revealed associations in both directions (i.e., a decrease in BMI had one effect, while an increase in BMI had the opposite effect), the categorical analyses showed associations only in one direction of BMI change, not both; 2) for another one of these eight outcomes, the categorical analyses suggested an association with change in BMI, while this association was not shown in the continuous analyses (this is potentially a false positive association); 3) for the last of the eight outcomes, the continuous analyses suggested an association of change in BMI, while this association was not shown in the categorical analyses (this is potentially a false negative association). CONCLUSIONS Categorization of continuous predictor variables alters the results of analyses and could lead to different conclusions; therefore, researchers in rheumatology should avoid it.
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Affiliation(s)
- Zubeyir Salis
- The University of New South Wales, Centre for Big Data Research in Health, Kensington, NSW, Australia
| | - Blanca Gallego
- The University of New South Wales, Centre for Big Data Research in Health, Kensington, NSW, Australia
| | - Amanda Sainsbury
- School of Human Sciences, The University of Western Australia, Crawley, Perth, WA, 6009, Australia.
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Souto LR, Serrão PRMDS, Pisani GK, Tessarin BM, da Silva HF, Machado EDM, de Oliveira Sato T, Serrão FV. Immediate effects of hip strap and foot orthoses on self-reported measures and lower limb kinematics during functional tasks in individuals with patellofemoral osteoarthritis: protocol for a randomised crossover clinical trial. Trials 2022; 23:746. [PMID: 36064729 PMCID: PMC9446757 DOI: 10.1186/s13063-022-06676-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Accepted: 08/20/2022] [Indexed: 11/10/2022] Open
Abstract
Background Elevated patellofemoral joint stress has been associated with patellofemoral osteoarthritis (PFOA). Changes in lower limb kinematics, such as excessive femoral adduction and internal rotation and excessive rearfoot eversion during the stance phase of functional activities, may increase patellofemoral stress. There is a lack of studies that assess the effects of interventions for controlling femur and subtalar joint movements during functional activities on self-reported measures in individuals with PFOA. Thus, the primary aim of the study is to determine the immediate effects of the hip strap and foot orthoses during level-ground walking and the single-leg squat test on self-reported outcomes. The secondary aim is to investigate whether the hip strap and foot orthoses result in the kinematic changes that these devices are purported to cause. Methods Twenty-nine individuals with PFOA aged 50 years or older will take part in the study. The main outcome is pain intensity. The secondary outcomes are other self-reported measures (global rating of change, acceptable state of symptoms, ease of performance, and confidence) and lower limb kinematics (peak femoral adduction and internal rotation, and peak rearfoot eversion). These outcomes will be assessed during functional tasks performed under three conditions: (i) control condition, (ii) hip strap intervention, and (iii) foot orthoses intervention. To investigate whether these interventions result in the lower limb kinematic changes that they are purported to cause, three-dimensional kinematics of the femur and rearfoot will be captured during each task. Linear mixed models with two fixed factors will be used to test associations between the interventions (control, hip strap, and foot orthoses) and conditions (level-ground walking and single-leg squat test) as well as interactions between the interventions and conditions. Discussion To the best of the authors’ knowledge, this is the first study to evaluate the immediate effects of the hip strap and foot orthoses on self-reported measures and lower limb kinematics during functional tasks in individuals with PFOA. The findings of this study will enable future trials to investigate the effects of these interventions in rehabilitation programmes. Trial registration ClinicalTrials.gov NCT04332900. Registered on 3 April 2020. Supplementary Information The online version contains supplementary material available at 10.1186/s13063-022-06676-0.
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Affiliation(s)
- Larissa Rodrigues Souto
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil.
| | | | - Giulia Keppe Pisani
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
| | - Bruna Mariana Tessarin
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
| | - Hygor Ferreira da Silva
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
| | - Eliane de Morais Machado
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
| | - Tatiana de Oliveira Sato
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
| | - Fábio Viadanna Serrão
- Department of Physical Therapy, Federal University of São Carlos, Rod. Washington Luís, Km 235, São Carlos, SP, CEP 13565-905, Brazil
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