The Role of Standardized Phase Angle in the Assessment of Nutritional Status and Clinical Outcomes in Cancer Patients: A Systematic Review of the Literature

Phase angle: A robust predictor of malnutrition and poor prognosis in gastrointestinal cancer

OBJECTIVES

The aim of this study was to investigate the relationship among phase angle (PA), malnutrition, and prognosis in patients with gastrointestinal cancer.

METHODS

In total, 870 patients with gastrointestinal cancer were enrolled. Kaplan-Meier curves and Cox proportional hazards models were used to evaluate the association between PA and survival risk. Restricted cubic spline regression was used for flexibility analysis to explore sex-specific associations between PA and survival. Logistic regression was used to assess the relationships among PA, malnutrition, and cachexia.

RESULTS

Low PA was closely associated with poor physical conditions, diminished quality of life, and malnutrition. Patients with low PA had a significantly worse prognosis than those with high PA (60.6% versus 72.8%; log-rank P < 0.001). PA was suitable for the prognostic assessment of patients with advanced-stage tumors. Regardless of sex, patients with lower PA showed significantly poorer survival rates. Cox proportional hazards models identified PA as an independent predictor of prognosis in patients with gastrointestinal cancer (hazard ratio (HR)=0.534; 95% confidence interval (CI)=0.409-0.696, P < 0.001). Subgroup analysis indicated that a high PA was an independent risk factor affecting the prognoses of patients with esophageal, liver, and intrahepatic bile duct cancers. Interestingly, variations in PA had a more significant prognostic effect on survival in men than in women. The logistic regression model confirmed that PA is a valuable indicator for assessing malnutrition and cachexia in patients with gastrointestinal cancer. Among all body composition indicators, PA demonstrated the highest accuracy for prognostic prediction.

CONCLUSIONS

PA was identified as a robust predictor of malnutrition and poor prognosis in patients with gastrointestinal cancer.

Bioimpedance formalism: A new approach for accessing the health status of cell and tissues

This manuscript describes a novel methodology for studying relaxation dynamics in tissues and cells using characteristic frequency of bioimpedance spectroscopy measurements. The Bioimpedance Formalism allows for the simultaneous study of bioelectrical parameters in the frequency and time domains, providing insight into possible relaxation processes occurring in the tissue or cell of interest. Results from the Cole-Cole analysis showed no multiple relaxation processes associated with heterogeneity, with a visible age group separation in males compared with females. The study of the relaxation dynamic in the time domain revealed that the β parameter can be used to analyse the charge carriers in tissues, cells, or cancer cells, potentially leading to new diagnostic and therapeutic approaches for cancer and other diseases. Overall, this approach presents a promising area of research for gaining insights into the electrical properties of tissues and cells using bioimpedance methods.

Bioimpedance-derived body composition parameters predict mortality and dose-limiting toxicity: the multicenter ONCO-BIVA study

BACKGROUND

In patients with cancer, lean body mass loss is frequent and associated with worse outcomes, including reduced treatment tolerance and survival. Bioelectrical impedance analysis (BIA) is a popular method for body composition assessment. We evaluated the value of BIA-derived body composition parameters in predicting mortality and, for the first time, dose-limiting toxicity (DLT).

PATIENTS AND METHODS

We conducted a prospective multicenter (n = 12) observational study in adult patients with solid neoplastic disease and receiving primary systemic treatment. We collected information on BIA-derived parameters: phase angle (PhA) <5th percentile of age and gender-specific normative values; standardized PhA (SPA) <-1.65; Nutrigram® <660 mg/24 h/m and <510 mg/24 h/m for males and females, respectively. The primary outcome and the key secondary were 1-year mortality and DLT (any-type severe toxicity requiring a delay in systemic treatment administration or a reduction of its dosage), respectively.

RESULTS

In total, 640 patients were included. At 12 months, death occurred in 286 patients (47.6%). All BIA-derived body composition parameters were independently associated with death: SPA, hazard ratio (HR) = 1.59 [95% confidence interval (CI) 1.30-1.95] (P < 0.001); PhA, HR = 1.38 (95% CI 1.13-1.69) (P = 0.002); Nutrigram®, HR = 1.71 (95% CI 1.42-2.04) (P < 0.001). DLT occurred in 208 patients (32.5%) and body composition parameters were associated with this outcome, particularly SPA: odds ratio = 6.37 (95% CI 2.33-17.44) (P < 0.001).

CONCLUSIONS

The study confirmed that BIA-derived body composition parameters are independently associated not only with survival but also with DLT. Although our findings were limited to patients receiving first-line systemic treatment, the evidence reported may have important practice implications for the improvement of the clinical work-up of cancer patients.

Predictive value of the random forest model based on bioelectrical impedance analysis parameter trajectories for short-term prognosis in stroke patients

BACKGROUND

The short-term prognosis of stroke patients is mainly influenced by the severity of the primary disease at admission and the trend of disease development during the acute phase (1-7 days after admission).

OBJECTIVE

The aim of this study is to explore the relationship between the bioelectrical impedance analysis (BIA) parameter trajectories during the acute phase of stroke patients and their short-term prognosis, and to investigate the predictive value of the prediction model constructed using BIA parameter trajectories and clinical indicators at admission for short-term prognosis in stroke patients.

METHODS

A total of 162 stroke patients were prospectively enrolled, and their clinical indicators at admission and BIA parameters during the first 1-7 days of admission were collected. A Group-Based Trajectory Model (GBTM) was employed to identify different subgroups of longitudinal trajectories of BIA parameters during the first 1-7 days of admission in stroke patients. The random forest algorithm was applied to screen BIA parameter trajectories and clinical indicators with predictive value, construct prediction models, and perform model comparisons. The outcome measure was the Modified Rankin Scale (mRS) score at discharge.

RESULTS

PA in BIA parameters can be divided into four separate trajectory groups. The incidence of poor prognosis (mRS: 4-6) at discharge was significantly higher in the "Low PA Rapid Decline Group" (85.0%) than in the "High PA Stable Group " (33.3%) and in the "Medium PA Slow Decline Group "(29.5%) (all P < 0.05). In-hospital mortality was the highest in the "Low PA Rapid Decline Group" (60%) compared with the remaining trajectory groups (P < 0.05). Compared with the prediction model with only clinical indicators (Model 1), the prediction model with PA trajectories (Model 2) demonstrated higher predictive accuracy and efficacy. The area under the receiver operating characteristic curve (AUC) of Model 2 was 0.909 [95% CI 0.863, 0.956], integrated discrimination improvement index (IDI), 0.035 (P < 0.001), and net reclassification improvement (NRI), 0.175 (P = 0.031).

CONCLUSION

PA trajectories during the first 1-7 days of admission are associated with the short-term prognosis of stroke patients. PA trajectories have additional value in predicting the short-term prognosis of stroke patients.

A Cross-Sectional Validation Study of Camry EH101 versus JAMAR Plus Handheld Dynamometers in Colorectal Cancer Patients and Their Correlations with Bioelectrical Impedance and Nutritional Status

BACKGROUND

Reduced muscle strength (dynapenia) and mass (atrophy) are prognostic factors in oncology. Measuring maximal handgrip strength with dynamometers is feasible but limited by the cost of the reference device (JAMAR).

METHODS

A cross-sectional study was conducted on colorectal cancer outpatients treated with chemotherapy or under active surveillance in our center from September 2022 to July 2023. Accuracy, reliability, and concordance were compared for two handheld dynamometers: the JAMAR Plus (the gold-standard device) and the Camry EH101 (a low-cost index device). A simultaneous nutritional diagnosis with GLIM criteria and bioelectrical impedance analysis (BIA) was carried out.

RESULTS

A total of 134 participants were included. The median of maximal strength for the JAMAR Plus had a non-significant difference of 1.4 kg from the Camry EH101. The accuracy and reliability of the devices were high. Bland-Altman analysis showed a 0.8 kg bias and -4.1 to 5.6 kg limits of agreement (LoA); a 0.1 kg bias and -5.3 to 5.4 kg LoA in men; a 1.5 kg bias and -2.2 to 5.3 kg LoA in women. In total, 29.85% of the participants were malnourished. Prevalence of dynapenia increased from 3.67% with the JAMAR Plus to 5.14% with the Camry EH101. Both devices had a moderate and significant correlation with BIA-estimated muscle mass.

CONCLUSIONS

The Camry EH101 was a cost-effective alternative to JAMAR Plus in our sample.

Predicting the Risk of Morbidity by GLIM-Based Nutritional Assessment and Body Composition Analysis in Oncologic Abdominal Surgery in the Context of Enhanced Recovery Programs : The PHase Angle Value in Abdominal Surgery (PHAVAS) Study

BACKGROUND

Preoperative nutritional status and body structure affect short-term prognosis in patients undergoing major oncologic surgery. Bioimpedance vectorial analysis (BIVA) is a reliable tool to assess body composition. Low BIVA-derived phase angle (PA) indicates a decline of cell membrane integrity and function. The aim was to study the association between perioperative PA variations and postoperative morbidity following major oncologic upper-GI surgery.

PATIENTS AND METHODS

Between 2019 and 2022 we prospectively performed BIVA in patients undergoing surgical resection for pancreatic, hepatic, and gastric malignancies on the day before surgery and on postoperative day (POD) 1. Malnutrition was defined as per the Global Leadership Initiative on Malnutrition criteria. The PA variation (ΔPA) between POD1 and preoperatively was considered as a marker for morbidity. Uni and multivariable logistic regression models were applied.

RESULTS

Overall, 542 patients with a mean age of 64.6 years were analyzed, 279 (51.5%) underwent pancreatic, 201 (37.1%) underwent hepatobiliary, and 62 (11.4%) underwent gastric resections. The prevalence of preoperative malnutrition was 16.6%. The overall morbidity rate was 53.3%, 59% in those with ΔPA < -0.5 versus 46% when ΔPA ≥ -0.5. Age [odds ratio (OR) 1.11; 95% confidence interval (CI) (1.00; 1.22)], pancreatic resections [OR 2.27; 95% CI (1.24; 4.18)], estimated blood loss (OR 1.20; 95% CI (1.03; 1.39)], malnutrition [OR 1.77; 95% CI (1.27; 2.45)], and ΔPA [OR 1.59; 95% CI (1.54; 1.65)] were independently associated with postoperative complications in the multivariate analysis.

CONCLUSIONS

Patients with preoperative malnutrition were significantly more likely to develop postoperative morbidity. Moreover, a decrease in PA on POD1 was independently associated with a 13% increase in the absolute risk of complications. Whether proactive interventions may reduce the downward shift of PA and the complication rate need further investigation.

Prognostic value of bioelectrical impedance analysis in head and neck cancer patients undergoing radiotherapy: a VALOR® study

Introduction

Bioelectrical impedance analysis (BIA) serves as a method to estimate body composition. Parameters such as phase angle (PA), standardized phase angle (SPA), body mass cell (BCM), BCM index (BCMI), and fat-free mass (FFM) might significantly impact the prognosis of head and neck cancer (HNC) patients. The present study aimed to investigate whether bioelectrical parameters can be used to predict survival in the HNC population and establish the optimal cutoff points for predictive accuracy.

Methods

A multicenter observational study was performed across 12 tertiary hospitals in Andalusia (a region from the south of Spain). A total of 494 patients diagnosed with HNC between 2020 and 2022 at different stages were included in this study, with a minimum follow-up period of 12 months. The BIA assessment was carried out during the first 2 weeks of radical radiotherapy treatment with chemotherapy or other systemic treatments. A multivariate logistic regression analysis of overall survival, complications, hospital admission, and palliative care and its relationship with BIA nutritional assessment was performed.

Results

Significant prognostic factors identified in the multivariable analysis encompassed phase angle (PA), standardized phase angle (SPA), body cell mass (BCM), and BCM index (BCMI). Lower PA and BCM values were significantly associated with adverse clinical outcomes. A BCM threshold above 17 kg/m2 was the most significant predictor for predicting survival within the overall HNC population. The PA values of <5.1° in male and <4.8° in female patients showed the best predictive potential for mortality. Increased PA (as a continuous variable) demonstrated a significantly reduced risk for mortality (OR, 0.64; 95% CI, 0.43-0.94; p < 0.05) and a decreased likelihood of hospital admission (OR, 0.75; 95% CI, 0.52-1.07; p < 0.05). Higher BCM correlated with a lower risk of mortality (OR, 0.88; 95% CI, 0.80-0.96; p < 0.01) and a diminished probability of hospital admission (OR, 0.91; 95% CI, 0.83-0.99; p < 0.05).

Conclusion

BIA is a crucial tool in the nutritional assessment of HNC patients. BCM and PA are the main bioelectrical parameters used to predict clinical outcomes in this population. Future studies are needed to validate BIA variables in a large cohort to ensure whether early intensification of nutritional treatment would improve survival.

Diagnostic Criteria and Measurement Techniques of Sarcopenia: A Critical Evaluation of the Up-to-Date Evidence

Sarcopenia, a geriatric syndrome characterized by progressive skeletal muscle mass and function decline, poses a significant health risk among the elderly, contributing to frailty, falls, hospitalization, loss of independence and mortality. The prevalence of sarcopenia varies significantly based on various factors, such as living status, demographics, measurement techniques and diagnostic criteria. Although the overall prevalence is reported at 10% in individuals aged 60 and above, disparities exist across settings, with higher rates in nursing homes and hospitals. Additionally, the differences in prevalence between Asian and non-Asian countries highlight the impact of cultural and ethnic factors, and variations in diagnostic criteria, cut-off values and assessment methods contribute to the observed heterogeneity in reported rates. This review outlines diverse diagnostic criteria and several measurement techniques supporting decision making in clinical practice. Moreover, it facilitates the selection of appropriate tools to assess sarcopenia, emphasizing its multifactorial nature. Various scientific groups, including the European Working Group of Sarcopenia in Older People (EWGSOP), the International Working Group on Sarcopenia (IWGS), the Asian Working Group on Sarcopenia (AWGS), the American Foundation for the National Institutes of Health (FNIH) and the Sarcopenia Definition and Outcomes Consortium (SDOC), have published consensus papers outlining diverse definitions of sarcopenia. The choice of diagnostic criteria should be aligned with the specific objectives of the study or clinical practice, considering the characteristics of the study population and available resources.

Flexibility and Strength Effects of Adapted Nordic Walking and Myofascial Exercises Practice in Breast Cancer Survivors and Analysis of Differences

Breast cancer treatments can elicit negative kinesiological side effects concerning both the posture and functional status of breast cancer survivors. As our body is functionally organized in myofascial meridians, physical exercise practice should favor a whole-body approach rather than a local one. The aim of the study was to investigate and compare the effects of two whole-body disciplines, i.e., adapted Nordic Walking and myofascial exercise, on the flexibility and strength performances in BCS. One hundred and sixty breast cancer survivors were trained three times per week for 12 weeks through adapted Nordic Walking or myofascial exercise. Handgrip, sit and reach, back scratch, and single leg back bridge tests and body composition were assessed at the beginning and completion of the training period. Linear mixed models showed no significant changes in body composition, whereas flexibility (p < 0.001), strength (p < 0.001), and muscle quality index (p = 0.003) changed independently from the treatment. When data modification has been analyzed according to sub-sample membership, no significant differences have been observed. Age, radiation therapy, and chemotherapy seem to have independent effects on several investigated variables. Twelve weeks of adapted myofascial exercise and Nordic Walking led to significant changes in flexibility, strength, and muscle quality in breast cancer survivors, with no apparent superiority of one approach over the other.

Effect of Regular Consumption of a Miraculin-Based Food Supplement on Taste Perception and Nutritional Status in Malnourished Cancer Patients: A Triple-Blind, Randomized, Placebo-Controlled Clinical Trial-CLINMIR Pilot Protocol

Taste disorders are common among cancer patients undergoing chemotherapy, with a prevalence ranging from 20% to 86%, persisting throughout treatment. This condition leads to reduced food consumption, increasing the risk of malnutrition. Malnutrition is associated not only with worse treatment efficacy and poor disease prognosis but also with reduced functional status and quality of life. The fruit of Synsepalum dulcificum (Daniell), commonly known as miracle berry or miracle fruit, contains miraculin, a taste-modifying protein with profound effects on taste perception. The CLINMIR Protocol is a triple-blind, randomized, placebo-controlled clinical trial designed to evaluate the regular consumption of a food supplement containing a miraculin-based novel food, dried miracle berry (DMB), on the taste perception (measured through electrogustometry) and nutritional status (evaluated through the GLIM Criteria) of malnourished cancer patients under active antineoplastic treatment. To this end, a pilot study was designed with 30 randomized patients divided into three study arms (150 mg DMB + 150 mg freeze-dried strawberries, 300 mg DMB, or placebo) for three months. Throughout the five main visits, an exhaustive assessment of different parameters susceptible to improvement through regular consumption of the miraculin-based food supplement will be conducted, including electrical and chemical taste perception, smell perception, nutritional and morphofunctional assessment, diet, quality of life, the fatty acid profile of erythrocytes, levels of inflammatory and cancer-associated cytokines, oxidative stress, antioxidant defense system, plasma metabolomics, and saliva and stool microbiota. The primary anticipated result is that malnourished cancer patients with taste distortion who consume the miraculin-based food supplement will report an improvement in food taste perception. This improvement translates into increased food intake, thereby ameliorating their nutritional status and mitigating associated risks. Additionally, the study aims to pinpoint the optimal dosage that provides maximal benefits. The protocol adheres to the SPIRIT 2013 Statement, which provides evidence-based recommendations and is widely endorsed as an international standard for trial protocols. The clinical trial protocol has been registered at the platform for Clinical Trials (NCT05486260).

Sarcopenia as a prognostic indicator in colorectal cancer: an updated meta-analysis

Background

Sarcopenia, often observed in the elderly, is associated with declining skeletal muscle mass and impaired muscle function. This condition has been consistently linked to a less favorable prognosis in various malignancies. Computed tomography (CT) is a frequently employed modality for evaluating skeletal muscle mass, enabling the measurement of the skeletal muscle index (SMI) at the third lumbar vertebra (L3) level. This measurement serves as a defining criterion for sarcopenia. The meta-analysis dealt with evaluating the promise sarcopenia held as a prognostic indicator in individuals with colorectal cancer.

Methods

Research relevant to the subject was determined by systematically searching PubMed, Embase, Web of Science, WANFANG, and CNKI (up to June 11, 2023, published studies). In this meta-analysis, the incidence of sarcopenia in individuals with colorectal cancer was combined to analyze the disease-free survival (DFS), overall survival (OS), and cancer-specific survival (CSS) of these individuals with and without sarcopenia. The included research was evaluated for quality per the Newcastle-Ottawa Scale (NOS) score. In the multivariate analysis of each study, the direct extraction of hazard ratio (HR) with a 95% confidence interval (CI) was executed. STATA 11.0 was applied to integrate and statistically analyze the data.

Results

Overall 20 articles participated in this meta-analysis. A 34% incidence of sarcopenia was noted in colorectal cancer. The presence of sarcopenia denoted a decrease in OS (HR=1.72,95% CI=1.45-2.03), DFS (HR=1.42,95% CI=1.26-1.60) and CSS (HR=1.48,95% CI=1.26-1.75) in individuals with colorectal cancer. In addition, the subgroup analysis depicted a pattern consistent with the overall analysis results.

Conclusion

CT-defined sarcopenia exhibits promise as an indicator of survival prognosis in individuals with colorectal cancer. Future studies need a more rigorous definition of sarcopenia to further verify these findings.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42023431435.

An analysis of phase angle and standard phase angle cut-off values and their association with survival in head and neck cancer patients undergoing radiotherapy

OBJECTIVE

The objective of this study is to identify the cutoff values for phase angle (PA) and standard phase angle (SPA) parameters, as determined by bioelectrical impedance analysis (BIA), for predicting malnutrition and investigating their association with overall survival in head and neck cancer (HNC) patients undergoing radiotherapy.

METHODS

In this study, nutritional assessment and follow-up of HNC patients undergoing radiotherapy (RT) between November 2017 and September 2022 were assessed. Nutritional assessment, body composition (BC), and PA results obtained from BIA (Tanita MC-980) were retrospectively evaluated. Statistical Package for Social Sciences (SPSS) version 25.0 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. The results were evaluated at a confidence interval of 95% and a significance level of p ≤ 0.05.

RESULTS

A total of 53 patients, including 37 (70%) men and 16 (30%) women, with a median age of 60 (23-87 years) were included. The median follow-up time was 51 (range 24-59) months. The mean PA of the patients was calculated as 4.99° (±0.92, 95% CI: 4.74-5.25). The PA of patients with malnutrition (4.66° ± 0.87) was lower than that of well-nourished patients (5.71° ± 0.56) (p < 0.001). As a result of the ROC analysis based on this finding, the ideal PA cut-off point for determining the presence of malnutrition was found to be 5.65, with a sensitivity of 85%, specificity of 79%, accuracy of 83%, and a model discrimination power of excellent level (AUC: 85%, p < 0.001). The median overall survival time of the patients was calculated as 51 months (24-59 months). The mortality rate during the follow-up period was 13%, while the 1-, 3-, and 5-year overall survival rates of the patients were 96.1%, 89.3%, and 86.8%, respectively. Patients with SPA values less than -1.65 had a 5-year overall survival rate of 77.4%, while those with SPA values greater than or equal to -1.65 had a 5-year overall survival rate of 100% (p = 0.030) CONCLUSION: Our study recommends using PA and SPA as standard criteria for detecting malnutrition in HNC patients undergoing RT, with cut-off points of 5.65 and -1.65 respectively, to prevent treatment interruptions and improve outcomes. Further research is needed to validate the SPA cut-off value and its relationship with clinical outcomes, as SPA may be a more effective predictor of malnutrition and overall survival than PA alone.

Recent Advances in Pancreatic Ductal Adenocarcinoma: Strategies to Optimise the Perioperative Nutritional Status in Pancreatoduodenectomy Patients

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy for which the mainstay of treatment is surgical resection, followed by adjuvant chemotherapy. Patients with PDAC are disproportionately affected by malnutrition, which increases the rate of perioperative morbidity and mortality, as well as reducing the chance of completing adjuvant chemotherapy. This review presents the current evidence for pre-, intra-, and post-operative strategies to improve the nutritional status of PDAC patients. Such preoperative strategies include accurate assessment of nutritional status, diagnosis and appropriate treatment of pancreatic exocrine insufficiency, and prehabilitation. Postoperative interventions include accurate monitoring of nutritional intake and proactive use of supplementary feeding methods, as required. There is early evidence to suggest that perioperative supplementation with immunonutrition and probiotics may be beneficial, but further study and understanding of the underlying mechanism of action are required.

Future lines of research on phase angle: Strengths and limitations

Bioelectrical impedance analysis (BIA) is the most widely used technique in body composition analysis. When we focus the use of phase sensitive BIA on its raw parameters Resistance (R), Reactance (Xc) and Phase Angle (PhA), we eliminate the bias of using predictive equations based on reference models. In particular PhA, have demonstrated their prognostic utility in multiple aspects of health and disease. In recent years, as a strong association between prognostic and diagnostic factors has been observed, scientific interest in the utility of PhA has increased. In the different fields of knowledge in biomedical research, there are different ways of assessing the impact of a scientific-technical aspect such as PhA. Single frequency with phase detection bioimpedance analysis (SF-BIA) using a 50 kHz single frequency device and tetrapolar wrist-ankle electrode placement is the most widely used bioimpedance approach for characterization of whole-body composition. However, the incorporation of vector representation of raw bioelectrical parameters and direct mathematical calculations without the need for regression equations for the analysis of body compartments has been one of the most important aspects for the development of research in this area. These results provide new evidence for the validity of phase-sensitive bioelectrical measurements as biomarkers of fluid and nutritional status. To enable the development of clinical research that provides consistent results, it is essential to establish appropriate standardization of PhA measurement techniques. Standardization of test protocols will facilitate the diagnosis and assessment of the risk associated with reduced PhA and the evaluation of changes in response to therapeutic interventions. In this paper, we describe and overview the value of PhA in biomedical research, technical and instrumental aspects of PhA research, analysis of Areas of clinical research (cancer patients, digestive and liver diseases, critical and surgical patients, Respiratory, infectious, and COVID-19, obesity and metabolic diseases, Heart and kidney failure, Malnutrition and sarcopenia), characterisation of the different research outcomes, Morphofunctional assessment in disease-related malnutrition and other metabolic disorders: validation of PhA with reference clinical practice techniques, strengths and limitations. Based on the detailed study of the measurement technique, some of the key issues to be considered in future PhA research. On the other hand, it is important to assess the clinical conditions and the phenotype of the patients, as well as to establish a disease-specific clinical profile. The appropriate selection of the most critical outcomes is another fundamental aspect of research.