No description available.

The main objective of the thesis was to compare two methods of calculating adjusted attributable fractions and deaths as applied to smoking exposure and four health outcomes, lung cancer, ischaemic heart disease, chronic obstructive pulmonary disease, and cerebrovascular disease, for Canadians 30 years or older in the year 2005. An additional objective was to calculate variance estimates for the evaluation of precision. Such estimates have not been published for Canada to date. Attributable fractions were calculated using the fully adjusted method and the partial adjustment method. This method requires confounder strata specific (stratified) estimates of relative risk, along with accompanying estimates of variance. These estimates have not previously been published, and were derived from the Cancer Prevention Study II cohort. Estimates of the prevalence of smoking in Canada were obtained from the Canadian Community Health Survey 2005. Variance estimates were calculated using a Monte Carlo simulation. The fully adjusted method produced smaller attributable fractions in each of the eight disease-sex-specific categories than the partially adjusted method. This suggests an upwards bias when using the partial adjustment method in the attributable fraction for the relationship between cigarette smoking and cause-specific mortality in Canadian men and women. Summed across both sexes and the four smoking related causes of death, the number of deaths attributable to smoking was estimated to be 25,684 using the fully adjusted method and 28,466 using the partial adjustment method, an upward bias of over ten percent, or 2,782 deaths. It is desirable, theoretically, to use methods which can fully adjust for the effect of confounding and effect modification. Given the large datasets required and access to original data, using these methods may not be feasible for some who would wish to do so.

The main objective of the thesis was to compare two methods of calculating adjusted attributable fractions and deaths as applied to smoking exposure and four health outcomes, lung cancer, ischaemic heart disease, chronic obstructive pulmonary disease, and cerebrovascular disease, for Canadians 30 years or older in the year 2005. An additional objective was to calculate variance estimates for the evaluation of precision. Such estimates have not been published for Canada to date. Attributable fractions were calculated using the fully adjusted method and the partial adjustment method. This method requires confounder strata specific (stratified) estimates of relative risk, along with accompanying estimates of variance. These estimates have not previously been published, and were derived from the Cancer Prevention Study II cohort. Estimates of the prevalence of smoking in Canada were obtained from the Canadian Community Health Survey 2005. Variance estimates were calculated using a Monte Carlo simulation. The fully adjusted method produced smaller attributable fractions in each of the eight disease-sex-specific categories than the partially adjusted method. This suggests an upwards bias when using the partial adjustment method in the attributable fraction for the relationship between cigarette smoking and cause-specific mortality in Canadian men and women. Summed across both sexes and the four smoking related causes of death, the number of deaths attributable to smoking was estimated to be 25,684 using the fully adjusted method and 28,466 using the partial adjustment method, an upward bias of over ten percent, or 2,782 deaths. It is desirable, theoretically, to use methods which can fully adjust for the effect of confounding and effect modification. Given the large datasets required and access to original data, using these methods may not be feasible for some who would wish to do so.

Objective: This study attempts to estimate the proportion of incident cases of bladder cancer in Ontario, Canada that is due to exposure to occupational carcinogens. Methods: The population attributable risk approach is used to estimate the proportion of bladder cancer in Ontario that is due to occupation. Risk ratios were obtained from a review of epidemiologic literature using a priori inclusion and exclusion criteria. Summary risk estimates for each bladder carcinogen included were calculated using RevMan 4.2. The CAREX Canada database provided Ontario-specific estimates of the proportion of workers exposed to bladder carcinogens. Results: In Ontario, the proportion of bladder cancer due to occupational exposure is approximately 5.6% (95% CI 0.2% to 14%). Based on the incident number of bladder cancer cases in 2001 in Ontario, it is estimated that approximately 52 new cases of bladder cancer were due to occupational exposure to polycyclic aromatic hydrocarbons (PAHs), diesel exhaust, aromatic amines and 2-naphthylamine. An alternate interpretation is if these occupational exposures were eliminated, 52 cases of bladder cancer per year in Ontario alone could be avoided. Conclusion and Recommendations: The current study advances our knowledge of the extent to which specific occupational bladder carcinogens contribute to the overall bladder cancer burden in Ontario. The current study highlights the utility of the CAREX Canada database in advancing current knowledge on the burden of occupational cancer in Ontario. The methods used to estimate the proportion of bladder cancer attributable to occupational exposure in Ontario may be replicated to estimate the proportion of cancer in Ontario that is due to occupational exposure. / Thesis (Master, Community Health & Epidemiology) -- Queen's University, 2008-08-29 20:08:46.713

Campylobacter is currently the most common cause of acute bacterial diarrhoea in Australia among all the notified enteric pathogens with more than 15,000 cases each year. The incidence of notified campylobacteriosis has steadily increased during the past 15 years from 67.0/100,000 population in 1991 to 121.4/100,000 in 2005, though the factors contributing to this increase had not been studied. Adjusting for under-reporting there are, at this point in time, an estimated 225,000 infections occurring each year in Australia, most of which are sporadic in nature. Much of our knowledge in Australia about risk factors for sporadic disease has been based on overseas literature. Prior to the studies undertaken in this thesis, the epidemiology of Campylobacter infection had not been thoroughly studied in Australia, nor had there been any national studies examining risk factors for locally-acquired infection. The broad aim of this thesis was to examine in depth the descriptive epidemiology of Campylobacter infection in Australia, explore the reasons for the sustained increase in incidence of infection and to identify the major risk factors for locally acquired infection using a multi-centre case-control study design. The descriptive study of the epidemiology of campylobacteriosis in Australia was based on Australian notifiable disease surveillance data collected over a 15-year period between 1991 and 2005. This study described the key epidemiological characteristics of this disease in Australia and identified some significant differences in incidence trends across states and territories and among different age groups which had not been previously reported. The study identified gaps in our knowledge of this disease in Australia and made recommendations for future research including the investigation of factors associated with the decline in incidence of infection among children aged  4 years and further studies to identify age and sex-specific risk factors for infection. The issue of seasonality, transmission routes and infection was addressed and areas for further research were specified including longitudinal studies at a regional level that incorporate a comparison of human, animal and environmental genotypes. This study also provided strong compelling evidence to support the hypothesis that the increase in notification rates in Australia during this period represented a real increase in the incidence of infection and that the main driving force behind this rise has been the ongoing increase in chicken consumption among the Australian public. The multi-centre case-control study, involving 1,714 participants  5 years of age, identified the major foodborne and non-foodborne risk factors for Campylobacter infection among the general population in Australia. This study confirmed that chicken meat is a major source of sporadic infection in this country and is responsible for almost one-third of all cases that occur in the Australian community each year. Other independent risk factors for sporadic infection in Australia included consumption of offal and ownership of domestic dogs or chickens aged  6 months. The Nagelkerke R² value of 16% for the final multivariable model indicated a considerable proportion of our case-patients had unexplained risk factors. The combined population attributable risk (PAR) estimate for the independent foodborne risk factors in this study was 31%, which is considerably less than the 75% to 80% of cases in the general population which are thought to be caused through foodborne transmission. Possible explanations for these results include the likelihood that a proportion of foodborne transmission in Australia occurs through food vehicles other than chicken due to cross-contamination from raw products, and the likelihood that much of the population attributable risk that is unaccountered for, may in fact be due to inherent limitations of study design resulting in systematic errors (information bias) and possibly reduced estimates of effect. The burden of illness among the general population in Australia attributable to different independent risk factors was estimated using a novel method developed specifically for this study. Briefly, community incidence data was coupled with PAR data from the case-control study and simulation techniques were used to: (i) estimate the number of infections attributable to specific risk factors, and (ii) derive credible intervals for these estimates by modeling the uncertainty in each variable component. This model of using case-control data in conjunction with pre-existing surveillance data provides researchers with a simple but robust tool for conducting source attribution studies on enteric pathogens. In conclusion, the studies undertaken in this thesis have made important contributions to our understanding of the epidemiology of sporadic Campylobacter infection in Australia.

No description available.

This project discusses some of the methodologies developed over the years to estimate attributable risk among exposed persons and the attributable risk in the entire population (also called Etiologic Fraction). It provides a general framework for estimating attributable risk among the exposed (denoted lambda_e). By making use of the recent observation that the two measures of attributable risk can be linked through the prevalence of the risk factor among the cases (denoted V_x), an estimate of population attributable risk (denoted lambda) for matched case-control studies is determined. Using the methodology developed recently by Kuritz and Landis (1987), this project provides explicit formulas for estimating the attributable risk among the exposed and the population attributable risk, and their large sample variances. This has been done both in situations where exactly R controls have been matched to a case and for a variable number of controls per case. The methodologies are illustrated with data from some case-control studies reported in the literature. Asymptotic relative efficiencies of different matching designs computed in terms of the costs of gathering cases and controls, are presented, together with some recommendations on what design is considered optimal. / Thesis / Master of Science (MSc)

Introdução: O Acinetobacter spp. é um cocobacilo gram-negativo de grande importância nas infecções hospitalares, especialmente em pacientes internados em unidades de terapia intensiva (UTI); podendo levar a um aumento na morbidade e mortalidade desses pacientes. Há evidências sustentando associação entre infecção por Acinetobacter baumannii e aumento das taxas de mortalidade bruta e atribuível. Contudo, o papel desse agente como causa direta de mortalidade ainda não está suficientemente caracterizado. Dentre os fatores relacionados com o aumento da mortalidade estão: gravidade do paciente, infecção relacionada à A. baumannii multirresistente, tratamento com antimicrobiano inadequado, tempo de hospitalização com alta permanência, choque séptico e imunossupressão. Objetivos: Estimar a mortalidade bruta e atribuível às infecções hospitalares causadas pelo Acinetobacter baumannii resistente a antimicrobianos carbapenêmicos (CRAB) por meio de revisão sistemática e metanálise de estudos observacionais. Métodos: Foi desenvolvida uma revisão sistemática e metanálise de estudos observacionais publicados nas bases de dados: MEDLINE/Pubmed, CENTRAL/Cochrane Library, EMBASE/Elsevier, SCOPUS/Elsevier, Web of Science/Thomson Reuters e LILACS/BVS, para estimar a mortalidade bruta e atribuível à infecção hospitalar causada pela bactéria A. baumannii resistente a antimicrobianos carbapenêmicos em pacientes adultos e pediátricos internados em unidades de tratamento intensivo e nãointensivo. Os estudos incluídos caracterizaram fatores preditores de mortalidade associada à infecção por CRAB, comparando com pacientes infectados por A. baumannii sensível a carbapenêmicos (CSAB). Primeiramente, foi estimado um modelo de efeitos aleatórios para a medida agregada de mortalidade atribuível não ajustado a fim de avaliar a contribuição direta das infecções na morte. Na sequência, foram avaliados descritivamente os principais aspectos metodológicos necessários aos estudos observacionais, para a análise dos fatores de risco relacionados a mortalidade atribuível em pacientes infectados por CRAB, por meio de instrumento elaborado conforme recomendações internacionais - ORION, TREND, STROBE e CONSORT. Resultados: Com base nos 29 estudos incluídos na metanálise, observou-se um risco atribuível aumentado na mortalidade bruta em pacientes com infecção por CRAB comparativamente aos pacientes com infecção por CSAB (RA = 0,19 (IC95% = 0,14-0,24) com elevada heterogeneidade (I2 = 66,4%, p-valor < 0,001). Como fontes de heterogeneidade investigou-se o tempo de internação, sítio de infecção, gravidade da doença e uso de terapia inapropriada. Entre os estudos que avaliaram exclusivamente pacientes com bacteremia, o risco de mortalidade atribuível foi maior (RA = 0,27; IC95% = 0,19-0,34). Utilizando-se metarregressão foi observada relação linear positiva entre o risco atribuível de mortalidade e a diferença da média padronizada do escore de APACHE II. Para a investigação da presença de risco de viés e confundimento avaliou-se descritivamente os principais aspectos metodológicos necessários aos estudos observacionais que identificam os fatores de risco associados com a mortalidade atribuível em pacientes com infecções por CRAB. Observou-se nesta revisão que os estudos estão sujeitos a confundimento, incluindo a forma inadequada do ajuste para fatores de confusão de variáveis importantes (ex.: seleção de grupo controle, exposição prévia aos antimicrobianos, mensuração do tempo em risco e a gravidade), além da grande heterogeneidade entre os estudos, devido aos desenhos, unidades de análise e abordagens na medida de exposição e desfecho, tornando difícil a comparação e a sumarização das informações. Conclusões: Os dados dessa revisão sistemática fornecem evidências que a mortalidade atribuível relacionada à presença de infecção por CRAB é maior que em pacientes com infecção por CSAB. Contudo, a investigação da mortalidade atribuível apresenta muitas limitações e ainda não é conclusiva em razão da adequação do desenho do estudo aos seus objetivos; definições de medidas de exposição e desfecho; métricas utilizadas na aferição dos resultados; seleção de grupo controle e fatores de confusão. A consciência de todos esses elementos para a interpretação epidemiológica é vital na análise da mortalidade bruta e atribuível. / Introduction: Acinetobacter spp. is a gram-negative coccobacillus of great importance in hospital infections, especially in patients in intensive care units (ICUs); may lead to an increase in morbidity and mortality of these patients. There is evidence supporting association between infection by Acinetobacter baumannii and the increase in crude and attributable mortality rates. However, the role of this agent as a direct cause of death is not sufficiently characterized yet. Among the factors related to the increase of mortality are: severity of the patient, infection related to A. baumannii multidrug-resistant, inappropriate antimicrobial treatment, hospital stay with high permanence, septic shock and immunosuppression. Objectives: To estimate the crude and attributable mortality to hospital-acquired infections caused by carbapenem-resistant Acinetobacter baumannii through systematic review and meta-analysis of observational studies. Methods: A systematic review and metaanalysis of observational studies published in the databases has been developed: MEDLINE/PubMed, CENTRAL/Cochrane Library, EMBASE/Elsevier, SCOPUS/Elsevier, Web of Science/Thomson Reuters and LILACS/BVS to estimate the crude and attributable mortality to hospital infection caused by the bacterium carbapenem-resistant A. baumannii (CRAB) in adult and pediatric patients in intensive and non-intensive care units. The studies included characterized predictors of mortality associated to infection with CRAB, compared to patients infected with carbapenem-susceptible A. baumannii (CSAB). First, a random effects model was estimated for the aggregate measure of non-adjusted attributable mortality in order to assess the direct contribution of infections in death. Following were descriptively assessed the main methodological aspects necessary to observational studies for the evaluation of risk factors related to attributable mortality in patients infected with carbapenem-resistant A. baumannii through instrument designed according to international recommendations - ORION, TREND, STROBE and CONSORT. Results: Through the 29 studies included in the meta-analysis, there was an increased attributable risk in the crude mortality in patients with infections by CRAB compared to patients with infections by CSAB (RA = 0.19 (95% CI = 0.14 to 0.24) with high heterogeneity (I2 = 66.4%, p <0.001). As sources of heterogeneity, it was investigated the length of stay, the site of infection, disease severity and use of inappropriate therapy. Among the studies that evaluated only patients with bacteremia, the risk of attributable mortality was higher (RA = 0.27; 95% CI = 0.19 to 0.34). Using meta-regression was observed a positive linear relationship between the attributable mortality risk and the standardized mean difference of APACHE II score. For investigating the presence of bias and confounding risk was evaluated descriptively the main methodological aspects necessary to observational studies evaluating the risk factors associated with attributable mortality in patients with infections caused by carbapenem-resistant A. baumannii. It was observed in this review that these studies are subject to pitfalls, including the inappropriate mode for adjustment for confounding factors of important variables (eg.: control group selection, previous exposure to antimicrobials, measurement of time in risk and gravity); besides the great heterogeneity between studies due the drawings, units of analysis and approaches to the extent of exposure and outcome, making it difficult comparison and summarization of information. Conclusions: The data of this systematic review provide evidence that attributable mortality related to the presence of infection by CRAB is higher than in patients with infection by CSAB. However, the investigation of attributable mortality has many limitations and is not conclusive yet because of the design adequacy of the study to their goals, definitions of exposure and outcome measures, metrics used in measuring results, control group selection and confounding factors. The awareness of all these elements is vital in analyzing the crude and attributable mortality.

Introduction: Clostridium difficile infection (CDI) is a common hospital-acquired infection and a financial burden on the healthcare system. There is a need to reduce its impact on patients and the entire health system. More accurate estimates of the financial impact of CDI will assist hospitals in creating better CDI reduction strategies with limited resources. Previous research has not sufficiently accounted for the skewed nature of hospital cost data, baseline patient mortality risk, and the time-varying nature of CDI. Objective: We conducted a retrospective cohort study to estimate the cost impact of hospital-acquired CDI from the hospital perspective, using a number of analytical approaches. Method: We used clinical and administrative data for inpatients treated at The Ottawa Hospital to construct an analytical data set. Our primary outcome was direct costs and our primary exposure was hospital-acquired CDI. We performed the following analyses: Ordinary least square regression and generalized linear regression as time-fixed methods, and Kaplan-Meier survival curve and Cox regression models as time-varying methods. Results: A total of 49,888 admissions were included in this study (mean (SD) age of 64.6 ± 17.8 years, median (IQR) baseline mortality risk of 0.04 (0.01-0.14)). 360 (0.73%) patients developed CDI. Estimates of incremental cost due to CDI were substantially higher when using time-fixed methods than time-varying methods. Using methods that appropriately account for the time-varying nature of the exposure, the estimated incremental cost due to CDI was $8,997 per patient. In contrast, estimates from time-fixed methods ranged from $49,150 to $55,962: about a six fold difference. Conclusion: Estimates of hospital costs are strongly influenced by the time-varying nature of CDI as well as baseline mortality risk. If studies do not account for these factors, it is likely that the impact of hospital-acquired CDI will be overestimated.

Introdução: O Acinetobacter spp. é um cocobacilo gram-negativo de grande importância nas infecções hospitalares, especialmente em pacientes internados em unidades de terapia intensiva (UTI); podendo levar a um aumento na morbidade e mortalidade desses pacientes. Há evidências sustentando associação entre infecção por Acinetobacter baumannii e aumento das taxas de mortalidade bruta e atribuível. Contudo, o papel desse agente como causa direta de mortalidade ainda não está suficientemente caracterizado. Dentre os fatores relacionados com o aumento da mortalidade estão: gravidade do paciente, infecção relacionada à A. baumannii multirresistente, tratamento com antimicrobiano inadequado, tempo de hospitalização com alta permanência, choque séptico e imunossupressão. Objetivos: Estimar a mortalidade bruta e atribuível às infecções hospitalares causadas pelo Acinetobacter baumannii resistente a antimicrobianos carbapenêmicos (CRAB) por meio de revisão sistemática e metanálise de estudos observacionais. Métodos: Foi desenvolvida uma revisão sistemática e metanálise de estudos observacionais publicados nas bases de dados: MEDLINE/Pubmed, CENTRAL/Cochrane Library, EMBASE/Elsevier, SCOPUS/Elsevier, Web of Science/Thomson Reuters e LILACS/BVS, para estimar a mortalidade bruta e atribuível à infecção hospitalar causada pela bactéria A. baumannii resistente a antimicrobianos carbapenêmicos em pacientes adultos e pediátricos internados em unidades de tratamento intensivo e nãointensivo. Os estudos incluídos caracterizaram fatores preditores de mortalidade associada à infecção por CRAB, comparando com pacientes infectados por A. baumannii sensível a carbapenêmicos (CSAB). Primeiramente, foi estimado um modelo de efeitos aleatórios para a medida agregada de mortalidade atribuível não ajustado a fim de avaliar a contribuição direta das infecções na morte. Na sequência, foram avaliados descritivamente os principais aspectos metodológicos necessários aos estudos observacionais, para a análise dos fatores de risco relacionados a mortalidade atribuível em pacientes infectados por CRAB, por meio de instrumento elaborado conforme recomendações internacionais - ORION, TREND, STROBE e CONSORT. Resultados: Com base nos 29 estudos incluídos na metanálise, observou-se um risco atribuível aumentado na mortalidade bruta em pacientes com infecção por CRAB comparativamente aos pacientes com infecção por CSAB (RA = 0,19 (IC95% = 0,14-0,24) com elevada heterogeneidade (I2 = 66,4%, p-valor < 0,001). Como fontes de heterogeneidade investigou-se o tempo de internação, sítio de infecção, gravidade da doença e uso de terapia inapropriada. Entre os estudos que avaliaram exclusivamente pacientes com bacteremia, o risco de mortalidade atribuível foi maior (RA = 0,27; IC95% = 0,19-0,34). Utilizando-se metarregressão foi observada relação linear positiva entre o risco atribuível de mortalidade e a diferença da média padronizada do escore de APACHE II. Para a investigação da presença de risco de viés e confundimento avaliou-se descritivamente os principais aspectos metodológicos necessários aos estudos observacionais que identificam os fatores de risco associados com a mortalidade atribuível em pacientes com infecções por CRAB. Observou-se nesta revisão que os estudos estão sujeitos a confundimento, incluindo a forma inadequada do ajuste para fatores de confusão de variáveis importantes (ex.: seleção de grupo controle, exposição prévia aos antimicrobianos, mensuração do tempo em risco e a gravidade), além da grande heterogeneidade entre os estudos, devido aos desenhos, unidades de análise e abordagens na medida de exposição e desfecho, tornando difícil a comparação e a sumarização das informações. Conclusões: Os dados dessa revisão sistemática fornecem evidências que a mortalidade atribuível relacionada à presença de infecção por CRAB é maior que em pacientes com infecção por CSAB. Contudo, a investigação da mortalidade atribuível apresenta muitas limitações e ainda não é conclusiva em razão da adequação do desenho do estudo aos seus objetivos; definições de medidas de exposição e desfecho; métricas utilizadas na aferição dos resultados; seleção de grupo controle e fatores de confusão. A consciência de todos esses elementos para a interpretação epidemiológica é vital na análise da mortalidade bruta e atribuível. / Introduction: Acinetobacter spp. is a gram-negative coccobacillus of great importance in hospital infections, especially in patients in intensive care units (ICUs); may lead to an increase in morbidity and mortality of these patients. There is evidence supporting association between infection by Acinetobacter baumannii and the increase in crude and attributable mortality rates. However, the role of this agent as a direct cause of death is not sufficiently characterized yet. Among the factors related to the increase of mortality are: severity of the patient, infection related to A. baumannii multidrug-resistant, inappropriate antimicrobial treatment, hospital stay with high permanence, septic shock and immunosuppression. Objectives: To estimate the crude and attributable mortality to hospital-acquired infections caused by carbapenem-resistant Acinetobacter baumannii through systematic review and meta-analysis of observational studies. Methods: A systematic review and metaanalysis of observational studies published in the databases has been developed: MEDLINE/PubMed, CENTRAL/Cochrane Library, EMBASE/Elsevier, SCOPUS/Elsevier, Web of Science/Thomson Reuters and LILACS/BVS to estimate the crude and attributable mortality to hospital infection caused by the bacterium carbapenem-resistant A. baumannii (CRAB) in adult and pediatric patients in intensive and non-intensive care units. The studies included characterized predictors of mortality associated to infection with CRAB, compared to patients infected with carbapenem-susceptible A. baumannii (CSAB). First, a random effects model was estimated for the aggregate measure of non-adjusted attributable mortality in order to assess the direct contribution of infections in death. Following were descriptively assessed the main methodological aspects necessary to observational studies for the evaluation of risk factors related to attributable mortality in patients infected with carbapenem-resistant A. baumannii through instrument designed according to international recommendations - ORION, TREND, STROBE and CONSORT. Results: Through the 29 studies included in the meta-analysis, there was an increased attributable risk in the crude mortality in patients with infections by CRAB compared to patients with infections by CSAB (RA = 0.19 (95% CI = 0.14 to 0.24) with high heterogeneity (I2 = 66.4%, p <0.001). As sources of heterogeneity, it was investigated the length of stay, the site of infection, disease severity and use of inappropriate therapy. Among the studies that evaluated only patients with bacteremia, the risk of attributable mortality was higher (RA = 0.27; 95% CI = 0.19 to 0.34). Using meta-regression was observed a positive linear relationship between the attributable mortality risk and the standardized mean difference of APACHE II score. For investigating the presence of bias and confounding risk was evaluated descriptively the main methodological aspects necessary to observational studies evaluating the risk factors associated with attributable mortality in patients with infections caused by carbapenem-resistant A. baumannii. It was observed in this review that these studies are subject to pitfalls, including the inappropriate mode for adjustment for confounding factors of important variables (eg.: control group selection, previous exposure to antimicrobials, measurement of time in risk and gravity); besides the great heterogeneity between studies due the drawings, units of analysis and approaches to the extent of exposure and outcome, making it difficult comparison and summarization of information. Conclusions: The data of this systematic review provide evidence that attributable mortality related to the presence of infection by CRAB is higher than in patients with infection by CSAB. However, the investigation of attributable mortality has many limitations and is not conclusive yet because of the design adequacy of the study to their goals, definitions of exposure and outcome measures, metrics used in measuring results, control group selection and confounding factors. The awareness of all these elements is vital in analyzing the crude and attributable mortality.