Bone mineral density and risk of cardiovascular disease in men and women: the HUNT study
AbstractThe association between bone mineral density (BMD) and cardiovascular disease (CVD) is not fully understood. We evaluated BMD as a risk factor for cardiovascular disease and specifically atrial fibrillation (AF), acute myocardial infarction (AMI), ischemic (IS) and hemorrhagic stroke (HS) and heart failure (HF) in men and women. This prospective population cohort utilized data on 22 857 adults from the second and third surveys of the HUNT Study in Norway free from CVD at baseline. BMD was measured using single and dual-energy X-ray absorptiometry in the non-dominant distal forearm and T-score was calculated. Hazard...
Source: European Journal of Epidemiology - September 13, 2021 Category: Epidemiology Source Type: research

Low and high pancreatic amylase is associated with pancreatic cancer and chronic pancreatitis
AbstractIncidences of pancreatic cancer and acute and chronic pancreatitis are rising globally, and often no curative treatment is available at the time of diagnosis. We tested the hypothesis that low and high plasma concentrations of pancreatic amylase are associated with increased risk of pancreatic cancer, acute pancreatitis, and chronic pancreatitis in the general population. We included 101,765 individuals (55% women) aged 20 –100 years from the Copenhagen General Population Study with baseline measurements of plasma pancreatic amylase. After recruitment in 2004–2015 during a median 9 years of fo...
Source: European Journal of Epidemiology - September 5, 2021 Category: Epidemiology Source Type: research

Alcohol intake and risk of glioma: results from three prospective cohort studies
ConclusionThese results provide evidence against a positive association between alcohol intake and glioma risk. Alcohol intake was associated with reduced risk of glioma in both men and women. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - September 4, 2021 Category: Epidemiology Source Type: research

Methodical considerations on adjusting for Charlson Comorbidity Index in epidemiological studies
In conclusion, the choice of CCI adjustment strategy impacts mitigation of bias in this simulation study, and suboptimal adjustment strategies can cause an observable bias, althoug h of quite limited magnitude of only a few percent in this simulation example. Researcher should be careful when deciding on the adjustment strategies applied to ensure that the desired mitigation of bias sources is achieved. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - September 4, 2021 Category: Epidemiology Source Type: research

Alcohol intake and risk of glioma: results from three prospective cohort studies
ConclusionThese results provide evidence against a positive association between alcohol intake and glioma risk. Alcohol intake was associated with reduced risk of glioma in both men and women. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - September 4, 2021 Category: Epidemiology Source Type: research

Methodical considerations on adjusting for Charlson Comorbidity Index in epidemiological studies
In conclusion, the choice of CCI adjustment strategy impacts mitigation of bias in this simulation study, and suboptimal adjustment strategies can cause an observable bias, althoug h of quite limited magnitude of only a few percent in this simulation example. Researcher should be careful when deciding on the adjustment strategies applied to ensure that the desired mitigation of bias sources is achieved. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - September 4, 2021 Category: Epidemiology Source Type: research

Consumption of red meat and processed meat and cancer incidence: a systematic review and meta-analysis of prospective studies
AbstractRed meat and processed meat consumption has been hypothesized to increase risk of cancer, but the evidence is inconsistent. We performed a systematic review and meta-analysis of prospective studies to summarize the evidence of associations between consumption of red meat (unprocessed), processed meat, and total red and processed meat with the incidence of various cancer types. We searched in MEDLINE and EMBASE databases through December 2020. Using a random-effect meta-analysis, we calculated the pooled relative risk (RR) and 95% confidence intervals (CI) of the highest versus the lowest category of red meat, proce...
Source: European Journal of Epidemiology - August 29, 2021 Category: Epidemiology Source Type: research

Exploring domains, clinical implications and environmental associations of a deep learning marker of biological ageing
AbstractDeep Neural Networks (DNN) have been recently developed for the estimation of Biological Age (BA), the hypothetical underlying age of an organism, which can differ from its chronological age (CA). Although promising, these population-specific algorithms  warrant further characterization and validation, since their biological, clinical and environmental correlates remain largely unexplored. Here, an accurate DNN was trained to compute BA based on 36 circulating biomarkers in an Italian population (N = 23,858; age ≥ 35 years; 51.7% women) . This estimate was heavily influenced...
Source: European Journal of Epidemiology - August 28, 2021 Category: Epidemiology Source Type: research

The origin of Modern Epidemiology, the book
(Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - August 28, 2021 Category: Epidemiology Source Type: research

Exploring domains, clinical implications and environmental associations of a deep learning marker of biological ageing
AbstractDeep Neural Networks (DNN) have been recently developed for the estimation of Biological Age (BA), the hypothetical underlying age of an organism, which can differ from its chronological age (CA). Although promising, these population-specific algorithms  warrant further characterization and validation, since their biological, clinical and environmental correlates remain largely unexplored. Here, an accurate DNN was trained to compute BA based on 36 circulating biomarkers in an Italian population (N = 23,858; age ≥ 35 years; 51.7% women) . This estimate was heavily influenced...
Source: European Journal of Epidemiology - August 28, 2021 Category: Epidemiology Source Type: research

The origin of Modern Epidemiology, the book
(Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - August 28, 2021 Category: Epidemiology Source Type: research

Suicide in prison and after release: a 17-year national cohort study
ConclusionThere is a high risk of suicide during the immediate first period of incarceration and after release. Convictions for severe violent crime, especially homicide, are associated with increased suicide risk, both in prison and after release. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - August 24, 2021 Category: Epidemiology Source Type: research

Rationale, design and population description of the CREDENCE study: cardiovascular risk equations for diabetes patients from New Zealand and Chinese electronic health records
AbstractThe cardiovascular risk equations for diabetes patients from New Zealand and Chinese electronic health records (CREDENCE) study is a unique prospectively designed investigation of cardiovascular risk in two large contemporary cohorts of people with type 2 diabetes from New Zealand (NZ) and China. The study was designed to derive equivalent cardiovascular risk prediction equations in a developed and a developing country, using the same epidemiological and statistical methodology. Two similar cohorts of people with type 2 diabetes were identified from large general population studies in China and New Zealand, which h...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Alcohol consumption in relation to cardiovascular diseases and mortality: a systematic review of Mendelian randomization studies
We reported the direction of the studied associations. Our search yielded 24 studies that were eligible for inclusion. A full instrumental variable analysis was performed in 17 studies (71%) and 13 out of 24 studies (54%) validated all three key assumptions. Five studies (21%) assessed potential non-linearity. In general, null associations were reported for genetically predicted alcohol consumption with the primary outcomes cardiovascular disease (67%) and diabetes (75%), while the only study on all-cause mortality reported a detrimental association. Considering the heterogeneity in methodological quality of the included M...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Prevalence of SARS-CoV-2 antibodies in Denmark: nationwide, population-based seroepidemiological study
We present results of consecutive population-based seroprevalence surveys performed in Denmark in 2020. In spring, late summer and autumn/winter of 2020, invitation letters including a questionnaire covering symptoms were sent to representative samples of the population above 12  years and to parents of children below 18 years in the sample. Blood samples were analysed for total Ig and seroprevalence estimates per population segment were calculated and compared to other surveillance parameters. Based on 34 081 participants (participation rate 33%), seroprevalence estimate s increased from 1.2% (95%CI: 0.3–1...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Maternal exposure to airborne polychlorinated biphenyls (PCBs) and risk of adverse birth outcomes
AbstractHuman health effects of airborne lower-chlorinated polychlorinated biphenyls (LC-PCBs) are largely unexplored. Since PCBs may cross the placenta, maternal exposure could potentially have negative consequences for fetal development. We aimed to determine if exposure to airborne PCB during pregnancy was associated with adverse birth outcomes. In this cohort study, exposed women had lived in PCB contaminated apartments at least one year during the 3.6  years before conception or the entire first trimester of pregnancy. The women and their children were followed for birth outcomes in Danish health registers. Logis...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Rationale, design and population description of the CREDENCE study: cardiovascular risk equations for diabetes patients from New Zealand and Chinese electronic health records
AbstractThe cardiovascular risk equations for diabetes patients from New Zealand and Chinese electronic health records (CREDENCE) study is a unique prospectively designed investigation of cardiovascular risk in two large contemporary cohorts of people with type 2 diabetes from New Zealand (NZ) and China. The study was designed to derive equivalent cardiovascular risk prediction equations in a developed and a developing country, using the same epidemiological and statistical methodology. Two similar cohorts of people with type 2 diabetes were identified from large general population studies in China and New Zealand, which h...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Alcohol consumption in relation to cardiovascular diseases and mortality: a systematic review of Mendelian randomization studies
We reported the direction of the studied associations. Our search yielded 24 studies that were eligible for inclusion. A full instrumental variable analysis was performed in 17 studies (71%) and 13 out of 24 studies (54%) validated all three key assumptions. Five studies (21%) assessed potential non-linearity. In general, null associations were reported for genetically predicted alcohol consumption with the primary outcomes cardiovascular disease (67%) and diabetes (75%), while the only study on all-cause mortality reported a detrimental association. Considering the heterogeneity in methodological quality of the included M...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Prevalence of SARS-CoV-2 antibodies in Denmark: nationwide, population-based seroepidemiological study
We present results of consecutive population-based seroprevalence surveys performed in Denmark in 2020. In spring, late summer and autumn/winter of 2020, invitation letters including a questionnaire covering symptoms were sent to representative samples of the population above 12  years and to parents of children below 18 years in the sample. Blood samples were analysed for total Ig and seroprevalence estimates per population segment were calculated and compared to other surveillance parameters. Based on 34 081 participants (participation rate 33%), seroprevalence estimate s increased from 1.2% (95%CI: 0.3–1...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Maternal exposure to airborne polychlorinated biphenyls (PCBs) and risk of adverse birth outcomes
AbstractHuman health effects of airborne lower-chlorinated polychlorinated biphenyls (LC-PCBs) are largely unexplored. Since PCBs may cross the placenta, maternal exposure could potentially have negative consequences for fetal development. We aimed to determine if exposure to airborne PCB during pregnancy was associated with adverse birth outcomes. In this cohort study, exposed women had lived in PCB contaminated apartments at least one year during the 3.6  years before conception or the entire first trimester of pregnancy. The women and their children were followed for birth outcomes in Danish health registers. Logis...
Source: European Journal of Epidemiology - August 22, 2021 Category: Epidemiology Source Type: research

Prediction or causality? A scoping review of their conflation within current observational research
AbstractEtiological research aims to uncover causal effects, whilst prediction research aims to forecast an outcome with the best accuracy. Causal and prediction research usually require different methods, and yet their findings may get conflated when reported and interpreted. The aim of the current study is to quantify the frequency of conflation between etiological and prediction research, to discuss common underlying mistakes and provide recommendations on how to avoid these. Observational cohort studies published in January 2018 in the top-ranked journals of six distinct medical fields (Cardiology, Clinical Epidemiolog...
Source: European Journal of Epidemiology - August 15, 2021 Category: Epidemiology Source Type: research

Association between body mass index, its change and cognitive impairment among Chinese older adults: a community-based, 9-year prospective cohort study
AbstractTo examine the association of baseline body mass index (BMI) and BMI change with cognitive impairment among older adults in China. The study included data from the Chinese Longitudinal Healthy Longevity Study, a national community-based prospective cohort study from 2002 to 2018. Baseline BMI and BMI change were available for 12,027 adults aged older than 65  years. Cognitive impairment was defined as Chinese version of the Mini Mental State Examination score lower than 18. Multivariable Cox proportional hazard model was used. Among 12,027 participants (mean age was 81.23 years old and 47.48% were ma...
Source: European Journal of Epidemiology - August 9, 2021 Category: Epidemiology Source Type: research

The association between meat and fish consumption and bladder cancer risk: a pooled analysis of 11 cohort studies
AbstractEvidence on the effects of meat consumption from different sources on the risk of bladder cancer (BC) is limited and controversial. Therefore, this study aimed to evaluate the associations between meat consumption and BC risk using a pooled data approach. Individual data from 11 prospective cohorts comprising 2848 BC cases and 515,697 non-cases with a total of 5,498,025 person-years of follow-up was pooled and analysed to investigate the potential associations between total red meat and products, red meat, processed meat, poultry and total fish and BC risk. Hazard ratios (HRs), with corresponding 95% confidence int...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

Systemic inflammation markers and cancer incidence in the UK Biobank
This study estimated associations between pre-diagnostic systemic inflammation markers and cancer risk in the prospective UK Biobank cohort of approximately 440,000 participants recruited between 2006 and 2010. We assessed associations between four immune-related markers based on blood cell counts: systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), and risk for 17 cancer sites by estimating hazard ratios (HR) using flexible parametric survival models. We observed positive associations with risk for seven out of 17 cancers w...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

Vegetable nitrate intake, blood pressure and incident cardiovascular disease: Danish Diet, Cancer, and Health Study
AbstractWhether the vascular effects of inorganic nitrate, observed in clinical trials, translate to a reduction in cardiovascular disease (CVD) with habitual dietary nitrate intake in prospective studies warrants investigation. We aimed to determine if vegetable nitrate, the major dietary nitrate source, is associated with lower blood pressure (BP) and lower risk of incident CVD. Among 53,150 participants of the Danish Diet, Cancer, and Health Study, without CVD at baseline, vegetable nitrate intake was assessed using a comprehensive vegetable nitrate database. Hazard ratios (HRs) were calculated using restricted cubic sp...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

Comparative effectiveness and safety of direct acting oral anticoagulants in nonvalvular atrial fibrillation for stroke prevention: a systematic review and meta-analysis
AbstractPurpose:To systematically review available evidence of indirect comparisons from RCTs and direct comparisons from observational studies regarding the comparative effectiveness and safety of DOACs in patients with AF.Methods: Electronic databases including EMBASE, MEDLINE, and PUBMED were searched up to June 5th, 2020. Primary endpoints included effectiveness (stroke or systemic embolism [SE]) and safety (major bleeding) outcomes. Bucher methods and random-effects models were conducted for indirect and direct comparisons among DOACs, respectively. Ranking probability analyses and the number needed to treat for net e...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

Parental age and birth defects: a sibling study
AbstractHigher parental age at childbearing has generated much attention as a potential risk factor for birth disorders; however, previous research findings are mixed. Existing studies have exploited variation in parental age across families, which is problematic because families differ not only in parental age but also in genetic and environmental factors. To isolate the effects of parental age, holding many genetic and environmental factors constant, we exploit the variation in parental age within families and compare outcomes for full siblings. The study data were retrieved from the Medical Birth Registry of Norway, whi...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

Sedentary behaviour in relation to ovarian cancer risk: a systematic review and meta-analysis
AbstractSedentary behaviour is an emerging risk factor for several site-specific cancers. Ovarian cancers are often detected at late disease stages and the role of sedentary behaviour as a modifiable risk factor potentially contributing to ovarian cancer risk has not been extensively examined. We systematically searched relevant databases from inception to February 2020 for eligible publications dealing with sedentary behaviour in relation to ovarian cancer risk. We conducted a systematic review and meta-analysis, calculating summary relative risks (RR) and 95% confidence intervals (CI) using a random-effects model. We cal...
Source: European Journal of Epidemiology - August 1, 2021 Category: Epidemiology Source Type: research

When intuition falters: repeated testing accuracy during an epidemic
AbstractWidespread, repeated testing using rapid antigen tests to proactively detect asymptomatic SARS-CoV-2 infections has been a promising yet controversial topic during the COVID-19 pandemic. Concerns have been raised over whether currently authorized lateral flow tests are sufficiently sensitive and specific to detect enough infections to impact transmission whilst minimizing unnecessary isolation of false positives. These concerns have often been illustrated using simple, textbook calculations of positivity rates and positive predictive value assuming fixed values for sensitivity, specificity and prevalence. However, ...
Source: European Journal of Epidemiology - July 28, 2021 Category: Epidemiology Source Type: research

Over- and under-estimation of COVID-19 deaths
AbstractThe ratio of COVID-19-attributable deaths versus “true” COVID-19 deaths depends on the synchronicity of the epidemic wave with population mortality; duration of test positivity, diagnostic time window, and testing practices close to and at death; infection prevalence; the extent of diagnosing without testing documentation; and the ratio of ove rall (all-cause) population mortality rate and infection fatality rate. A nomogram is offered to assess the potential extent of over- and under-counting in different situations. COVID-19 deaths were apparently under-counted early in the pandemic and continue to be...
Source: European Journal of Epidemiology - July 28, 2021 Category: Epidemiology Source Type: research

When intuition falters: repeated testing accuracy during an epidemic
AbstractWidespread, repeated testing using rapid antigen tests to proactively detect asymptomatic SARS-CoV-2 infections has been a promising yet controversial topic during the COVID-19 pandemic. Concerns have been raised over whether currently authorized lateral flow tests are sufficiently sensitive and specific to detect enough infections to impact transmission whilst minimizing unnecessary isolation of false positives. These concerns have often been illustrated using simple, textbook calculations of positivity rates and positive predictive value assuming fixed values for sensitivity, specificity and prevalence. However, ...
Source: European Journal of Epidemiology - July 28, 2021 Category: Epidemiology Source Type: research

Prevalence of SARS-CoV-2 RNA on inanimate surfaces: a systematic review and meta-analysis
AbstractCoronavirus disease (COVID-19) is a respiratory disease affecting many people and able to be transmitted through direct and perhaps indirect contact. Direct contact transmission, mediated by aerosols or droplets, is widely demonstrated, whereas indirect transmission is only supported by collateral evidence such as virus persistence on inanimate surfaces and data from other similar viruses. The present systematic review aims to estimate SARS-CoV-2 prevalence on inanimate surfaces, identifying risk levels according to surface characteristics. Data were obtained from studies in published papers collected from two data...
Source: European Journal of Epidemiology - July 27, 2021 Category: Epidemiology Source Type: research

Socioeconomic inequalities in dementia risk among a French population-based cohort: quantifying the role of cardiovascular health and vascular events
This study aimed to investigate the role of cardiovascular health (CVH) and vascular events as potential contributors to socioeconomic inequalities in dementia using causal mediation analyses. We used data from the Three-City Cohort, a French population-based study with 12  years of follow-up, with active search of dementia cases and validated diagnosis. Individual socioeconomic status was assessed using education, occupation and income. A CVH score as defined by the American Heart Association and incident vascular events were considered separately as mediators. We p erformed multi-level Cox proportional and Aalen add...
Source: European Journal of Epidemiology - July 25, 2021 Category: Epidemiology Source Type: research

Dementia risk in the general population: large-scale external validation of prediction models in the AGES-Reykjavik study
AbstractWe aimed to evaluate the external performance of prediction models for all-cause dementia or AD in the general population, which can aid selection of high-risk individuals for clinical trials and prevention. We identified 17 out of 36 eligible published prognostic models for external validation in the population-based AGES-Reykjavik Study. Predictive performance was assessed withc statistics and calibration plots. All five models with ac statistic  >  .75 (.76–.81) contained cognitive testing as a predictor, while all models with lowerc statistics (.67 –.75) did not. Calibration ranged ...
Source: European Journal of Epidemiology - July 25, 2021 Category: Epidemiology Source Type: research

Socioeconomic inequalities in dementia risk among a French population-based cohort: quantifying the role of cardiovascular health and vascular events
This study aimed to investigate the role of cardiovascular health (CVH) and vascular events as potential contributors to socioeconomic inequalities in dementia using causal mediation analyses. We used data from the Three-City Cohort, a French population-based study with 12  years of follow-up, with active search of dementia cases and validated diagnosis. Individual socioeconomic status was assessed using education, occupation and income. A CVH score as defined by the American Heart Association and incident vascular events were considered separately as mediators. We p erformed multi-level Cox proportional and Aalen add...
Source: European Journal of Epidemiology - July 25, 2021 Category: Epidemiology Source Type: research

Dementia risk in the general population: large-scale external validation of prediction models in the AGES-Reykjavik study
AbstractWe aimed to evaluate the external performance of prediction models for all-cause dementia or AD in the general population, which can aid selection of high-risk individuals for clinical trials and prevention. We identified 17 out of 36 eligible published prognostic models for external validation in the population-based AGES-Reykjavik Study. Predictive performance was assessed withc statistics and calibration plots. All five models with ac statistic  >  .75 (.76–.81) contained cognitive testing as a predictor, while all models with lowerc statistics (.67 –.75) did not. Calibration ranged ...
Source: European Journal of Epidemiology - July 25, 2021 Category: Epidemiology Source Type: research

Improving the reporting of non-inferiority trials by incorporating non-efficacy benefits: not all on-inferiority trials are created equal
AbstractNon-inferiority trials are used to test if a novel intervention is not worse than a standard treatment by more than a prespecified amount, the non-inferiority margin ( ΔNI). The ΔNI indicates the amount of efficacy loss in the primary outcome that is acceptable in exchange for non-efficacy benefits in other outcomes. However, non-inferiority designs are sometimes used when non-efficacy benefits are absent. Without non-efficacy benefits, loss in efficacy cannot b e easily justified. Further, non-efficacy benefits are scarcely defined or considered by trialists when determining the magnitude of and provid...
Source: European Journal of Epidemiology - July 19, 2021 Category: Epidemiology Source Type: research

Marital status and prostate cancer incidence: a pooled analysis of 12 case –control studies from the PRACTICAL consortium
AbstractWhile being in a committed relationship is associated with a better prostate cancer prognosis, little is known about how marital status relates to its incidence. Social support provided by marriage/relationship could promote a healthy lifestyle and an increased healthcare seeking behavior. We investigated the association between marital status and prostate cancer risk using data from the PRACTICAL Consortium. Pooled analyses were conducted combining 12 case –control studies based on histologically-confirmed incident prostate cancers and controls with information on marital status prior to diagnosis/interview....
Source: European Journal of Epidemiology - July 18, 2021 Category: Epidemiology Source Type: research

Re: Hofmann et al. Overdiagnosis, one concept, three perspectives, and a model
AbstractIt is with great interest we have read the article “Overdiagnosis: one concept, three perspectives, and a model” by Hofmann and colleagues. We share the authors’ ambition of understanding what overdiagnosis is and what it isn’t. In our research, we define overdiagnosis on the basis of two interrelated phenomena: overdetection and overdefinit ion. Overdetection is the labelling of a person with a disease or abnormal condition, that would not have caused the person harm, e.g., symptoms or death, if left undiscovered. Overdefinition is the creation of new diagnoses by overmedicalising ordinary ...
Source: European Journal of Epidemiology - July 18, 2021 Category: Epidemiology Source Type: research

Authors ’ reply to Grundtvig Gram et al.
(Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - July 18, 2021 Category: Epidemiology Source Type: research

Design, implementation and initial findings of COVID-19 research in the Rotterdam Study: leveraging existing infrastructure for population-based investigations on an emerging disease
This article provides an overview of the rationale, design, and implementation of this sub-st udy nested within the Rotterdam Study. Finally, initial results on participant characteristics and prevalence of COVID-19 in this community-dwelling population are shown. (Source: European Journal of Epidemiology)
Source: European Journal of Epidemiology - July 17, 2021 Category: Epidemiology Source Type: research