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Dich te moi truong dai hoc
 

Dich te moi truong dai hoc

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DH Y DUOC TP.HCM

DH Y DUOC TP.HCM
KHOA YTCC
BM DICH TE HOC
GIANG VIEN: TS. DO VAN DUNG

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  • Basic Study Designs Type of study Unit of study Descriptive studies Individuals or populations Analytical studies Ecological Populations Cross-sectional Individuals Cohort Individuals Case–control Individuals Experimental studies Randomized controlled trial Patients Field trials Healthy people Community trials Communities Descriptive Studies • Description of the health status of a population (community, nation, etc.) – Person, place, and time • No formal attempt to test hypothesis or link exposure and health outcome • Generally based on existing data – Birth or death statistics – Hospital discharge data – Health surveys
  • Descriptive Studies • Description of the health status of a population (community, nation, etc.) – Person, place, and time • No formal attempt to test hypothesis or link exposure and health outcome • Generally based on existing data – Birth or death statistics – Hospital discharge data – Health surveys
  • Ecological Studies • Unit of analysis is group or population, rather than individuals – Schools, factories, counties, or nations • Compare aggregate measure of health outcome with aggregate measure of exposure and covariates across groups – Spatial or temporal patterns • Generally based on existing data
  • Ecological Studies • Advantages – Can be done quickly and inexpensively, often using already available information – May be able to identify associations by examining greater range in exposure – May be able to evaluate ecological or contextual effects
  • Ecological Studies • Disadvantages – Quality of existing data may be limited – Cannot link exposure with disease in individuals • Ecological fallacy: pattern in aggregate data does not reflect relationships at individual level • Average exposure and disease data may mask more complex associations – Difficult to control for confounding effects and bias
  • Design of Cross-Sectional Study • Choose sampling frame for selecting study participants • Measure exposure and health outcome status of the study participants – Health outcomes are based on prevalence, not incidence of conditions
  • Cross-sectional Study of Respiratory Symptom Prevalence and Exposure to Automobile Exhaust Distance from Chronic No chronic roadside wheeze wheeze < 20 m 56 514 20–150 m 24 554 Odds ratio = 2.5
  • Limitations of Cross-Sectional Studies • Distinguishing incident versus prevalent cases • Interpreting temporal sequence • Selective survival of study subjects
  • Steps in a Cohort Study • Identify and select study population • Classify study population according to exposure status and other risk factors • Follow cohort members over time to determine health outcome occurrence by exposure status sub-groups
  • Examples of Cohort Studies • Populations exposed to radiation – Japanese populations who experienced WW II nuclear bomb explosions – Children who underwent radiation treatment for an enlarged thymus – Women treated with radiation for post-partum mastitis – Communities who were affected by the Chernobyl nuclear accident
  • Examples of Cohort Studies • Environmental poisoning episodes – Yusho Disease - due to ingestion of rice oil contaminated with polychlorinated biphenyls – Minamata - children living near Minamata who were exposed to methyl mercury • Populations exposed to acute releases of toxic chemicals from industrial facilities – Pesticide factory in Bhopal, India, from which methyl-isocynate leakage killed more than 2000 people and poisoned 200,000 others in 1984
  • Cohort Studies • Advantages – Can determine incidence rates and attributable risk directly – Exposure can be determined with less potential for bias than if outcome were already known – Can be efficient for studying rare exposures
  • Cohort Studies • Advantages – Can determine incidence rates and attributable risk directly – Exposure can be determined with less potential for bias than if outcome were already known – Can be efficient for studying rare exposures
  • Cohort Studies • Disadvantages – Inefficient, because must follow many more subjects than will experience the event of interest – Expensive – Results not available for long time – Bias due to attrition or loss to follow-up
  • Steps in a Case–Control Study • Establish a case definition • Identify sampling frame for selecting cases and controls • Assess prior exposure status and other risk factors for cases and controls • Compare prior exposure experiences of cases and controls in order to estimate association between exposures and health outcome
  • Examples of Case-Control Studies • Lung cancer and residential exposure to radon • Lung cancer and indoor air pollution in China • Leukemia in individuals exposed to radioactive fallout from nuclear testing facilities in the USA
  • Case-Control Studies • Advantages – Relatively efficient and inexpensive. Especially efficient for rare diseases – Useful for studying diseases with long latencies – Can assess the potential effects of several exposures on disease
  • Disadvantages – Difficulty selecting appropriate comparison group – Potential bias in measuring exposure: • Outcome may affect subject's recollection of the exposure • Outcome may affect the measurement or recording of the exposure – Cannot directly estimate attributable risk
  • Experimental Studies • “ Natural Experiments” – Monitor changes in health outcomes associated with change in environmental condition or regulation • Controlled human exposure studies – Respiratory and neurobehavioral effects of exposure to air pollutants or solvents – Reproductive hormone and immune mediators changes • Community trials
  • Community Trial : Permanent Teeth Decayed, Missing, or Filled (DMF) per 100 Children, Ages 6–16, Based on Clinical and Roentgenographic Examination Ten Years After Start of Fluoridation — New York, 1954–55 6–9 708 913 98.4 233.7 -57.9 10–12 521 640 328.1 698.6 -53 13–14 263 441 610.1 1170.3 -47.9 15–16 109 119 975.2 1648.7 -40.9
  • Outcome Nhiều hơn Ít hơn Như cũ Tỉ số Nhức đầu 25 16 31 1.6 Khô mũi 22 15 35 1.5 Xung huyết mũi 20 18 34 1.1 Ban 10 9 53 1.1 Chảy mũi 14 19 40 0.7 Ngủ gà 11 12 49 0.9
  • Experimental Studies Strengths Most definitive study design because investigators “assign” exposure Possible to evaluate effects of dose Able to study temporal relationships Weaknesses Limited to study of short-term, reversible effects of potentially harmful agents, or of treatment or preventive interventions. Generalizability when studying volunteers Potential high cost and lost to follow-up
  • Common Study Designs for Environmental Epidemiology • Community-based cross-sectional and case-control studies – Cancer studies using registry • Ecological studies – Spatial and temporal patterns • Increasing use of spatial mapping (GIS) • Time series studies – Ecological time-series – Panel studies
  • Time-series Studies • Correlation between changes in exposure over time with changes in outcome over time • Strengths – Communities or persons serve as their own controls (reduces confounding) • Weaknesses – Can study only reversible effects in individuals – Requires sophisticated statistical analysis • Time-series modeling (GEE, GAM) • Case-crossover analysis
  • Examples of Time-Series Studies • Ecological Studies – Variation in mortality, hospitalizations, and emergency room visits with changes in air pollution using aggregate data in major cities • Panel Studies – Variation in asthma symptoms, medication use, and peak flow with changes in exposure to air pollutants and fungal spores, measured via air and personal monitoring – Heart rate variability and exposure to ultrafine particles
  • Common Study Designs for Environmental Epidemiology • Community-based cross-sectional and case-control studies – Cancer studies using registry • Ecological studies – Spatial and temporal patterns • Increasing use of spatial mapping (GIS) • Time series studies – Ecological time-series – Panel studies
  • Time-series Studies • Correlation between changes in exposure over time with changes in outcome over time • Strengths – Communities or persons serve as their own controls (reduces confounding) • Weaknesses – Can study only reversible effects in individuals – Requires sophisticated statistical analysis • Time-series modeling (GEE, GAM) • Case-crossover analysis
  • Examples of Time-Series Studies • Ecological Studies – Variation in mortality, hospitalizations, and emergency room visits with changes in air pollution using aggregate data in major cities • Panel Studies – Variation in asthma symptoms, medication use, and peak flow with changes in exposure to air pollutants and fungal spores, measured via air and personal monitoring – Heart rate variability and exposure to ultrafine particles
  • - In summary, case crossover design is used when a brief exposure causes a transient change in risk of an acute onset event. The event can be the onset of type I diabetes, a motor vehicle accident, or an injury. The “exposure” can be another disease or certain activity, such as having an infectious disease, conducting a certain unusual task, or using a certain device. There is a hazard period associated with the event onset and the exposure information in the hazard period is compared with the control data from a selected control period. - In the next few slides I will formally introduce hazard period, effect period and control data.

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