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8 principle of epidemiology 11 community medicine

Epidemiologic methods are used to identify disease risk factors and determine optimal treatments. There are two main types of epidemiologic studies: observational studies and experimental studies. Observational studies include descriptive studies, which observe disease distribution, and analytical studies like cohort and case-control studies, which analyze associations between exposures and disease. Experimental studies include randomized controlled trials, which randomly assign participants to test interventions, and non-randomized trials.

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8 Community Medicine Principle of Epidemiology 11 Methods of Epidemiology Dr. Siham Gritly University of Bahri Dr. Siham Gritly 1
Dr. Siham Gritly 2 Epidemiologic methods are used for the identification of risk factors for disease and determination of optimal treatment approaches used in clinical practice
Methods of Epidemiology • Epidemiologic methods are used for; • -the identification of risk factors for disease • -and determination of optimal treatment approaches used in clinical practice. Dr. Siham Gritly 3
• In the study of communicable and chronic diseases, the work of epidemiologists involves; • study design, • data collection • and statistical analysis Dr. Siham Gritly 4
Epidemiological studies classified in two categories • 1-observational studies (non experimental studies) • A) descriptive studies • B) Analytical studies • 2-experimental studies (intervention studies) • A) Randomized Controlled trial or clinical trail • B) 2-non randomized or non-experimental trials Dr. Siham Gritly 5
1-observational studies • researcher observes association between exposure and disease, estimates and tests it • 1-observational studies Include; • A) descriptive studies • B) Analytical studies Dr. Siham Gritly 6
A) descriptive studies • Descriptive studies are usually the first phase of an epidemiological investigation • Observing the distribution of disease or health related characteristics in human population Dr. Siham Gritly 7
• In Descriptive studies questions should be asked such as; • When is the disease occurring----time distribution • Where it is occurring------place distribution • Who is getting the disease----persons distribution Dr. Siham Gritly 8
Procedures in Descriptive studies • 1-defining the population to be studied • 2-defing disease under study • 3-describing the disease by; • -time • Place • Person Dr. Siham Gritly 9
• 4-measurement of disease • 5-comparing with known indices • 6-formulation of an aetiological hypothesis Dr. Siham Gritly 10
• 1-defining the population to be studied • Descriptive study are investigation of population not individual; include total number • Sex • Age • Occupation • cultural Dr. Siham Gritly 11
• 2-defing disease under study; • Specified the disease to be investigated • The main objective to obtain accurate estimate of disease in a population Dr. Siham Gritly 12
• 3-describing the disease by; • The main primary objective of descriptive epidemiology is to describe the occurrence and distribution of disease by • Time-- • Place • person Dr. Siham Gritly 13
• 4-measurement of disease • The information should be available in terms of • Mortality • Morbidity (incidence and prevalence) • distribution Dr. Siham Gritly 14
• 5-comparing with known indices • Making comparisons between different population, this is to ; identify groups who are at risk for certain diseases Dr. Siham Gritly 15
• 6-formulation of an aetiological hypothesis • Hypothesis should formulated in a manner that that it can be tested Dr. Siham Gritly 16
• Hypothesis should specify the following • -the population- the characteristics of the persons to whom the hypothesis to be applied • -the specific cause being considered • -the expected outcome • -the dose-response relationship • -the time-response relationship (time between exposure to the cause observed) Dr. Siham Gritly 17
B) Analytical studies • Analytical studies are the second major type of epidemiological studies • In contrast to descriptive studies which look for the whole population the analytical studies look for individual within the population • Main types of observational studies are; • Case control study • Cohort study Dr. Siham Gritly 18
Cohort or follow up cohort study (prospective) ; -individual exposed to particular factors Presence or absence of particular diseaseIndividual unexposed to particular factors Dr. Siham Gritly 19 Typical analytical study designs: Cohort or follow up with individual as a unit of study. An example ; investigation of a cohort of smokers and non-smokers over time to estimate the incidence of lung cancer (prospective) ;
case-control or case-references Cases (disease present) Control (disease absent) Suspected or risk factors Individuals with particular disease Individual without particular disease Dr. Siham Gritly 20 case-control or case-references with individual as a unit of study select subjects based on their disease status. It is a retrospective study. -factors present or absent---Observational
• Cross-sectional or prevalence with individual as a unit of study • Ecological or correlation with population as unit of study Dr. Siham Gritly 21
Dr. Siham Gritly 22
2-experimental studies or Interventional: • Experimental studies are of two types • A-Randomized Controlled trial or clinical trail • B-non randomized or non-experimental trials • -field trials or community intervention studies • -Community trial Dr. Siham Gritly 23
A)-Randomized Controlled trial or clinical trail • A study design that randomly assigns participants into an experimental group or a control group. • As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied. Dr. Siham Gritly 24
• Design of randomized control trial; • The protocol; • Selecting reference and experimental population (make necessary exclusions) • Randomize of two • 1-experimental group • 2-control group • Follow up • assessment Dr. Siham Gritly 25
• Advantages • No population bias • Results can be analyzed with well known statistical tools • Populations of participating individuals are clearly identified Dr. Siham Gritly 26
• Disadvantages • Expensive in terms of time and money • biases: the population that participates may not be representative of the whole • Does not reveal causation • Loss to follow-up Dr. Siham Gritly 27
B-Non-randomized controlled trial • An experimental study in which people are allocated to different interventions using methods that are not random. Dr. Siham Gritly 28
Study Designs: Types • Qualitative • Quantitative Dr. Siham Gritly 29
Qualitative Quantitative Definition a systematic subjective approach used to describe life experiences and give them meaning a formal, objective, systematic process for obtaining information about the world. A method used to describe, test relationships, and examine cause and effect relationships. Goals To gain insight; explore the depth, richness, and complexity inherent in the phenomenon. To test relationships, describe, examine cause and effect relations Dr. Siham Gritly 30
Qualitative Quantitative Characteristic •Soft science •Focus: complex & broad •Subjective •Basis of knowing: meaning & discovery •Develops theory •Shared interpretation •Communication & observation •Basic element of analysis: words •Individual interpretation Hard science Focus: concise & narrow Objective Basis of knowing: cause & effect, relationships Tests theory Control Instruments Basic element of analysis: numbers Statistical analysis GeneralizationDr. Siham Gritly 31
Objective vs Subjective • Objective is a statement that is completely unbiased. • It is confirmable by looking up facts or performing mathematical calculations. • scientific facts are objective as are mathematical proofs; essentially anything that can be backed up with solid data. Dr. Siham Gritly 32
• Subjective is a statement that has been colored by the character of the speaker or writer. • It often has a basis in reality, • It cannot be verified using concrete facts and figures • Subjective : opinions, interpretations, and any type of marketing presentation are all subjective. Dr. Siham Gritly 33
references • Park's Textbook of Preventive and Social Medicine 21 Edition, by K. PARK Dr. Siham Gritly 34