Research and Methodology Prof Dr : Sameh Zaytoun Head of Community Medicine Department

Epidemiologic Studies

Epidemiologic Studies: The primary concern of the epidemiologist is to study Disease Occurrence among people, so he uses carefully designed research strategies to explore disease etiology. These strategies are of three main types: Descriptive Studies Analytical Studies Intervention Studies

Epidemiologic Studies: Descriptive Studies Clinical studies (Case report & Case series) Correlation studies Cross sectional studies (Distribution or Prevalence studies)

Epidemiologic Studies: Analytical Studies Case – Control Studies Cohort Studies

Epidemiologic Studies: Intervention Studies Preventive trials Clinical trials. Population trials

Descriptive Studies: Types of Descriptive Studies: Descriptive studies describe patterns of disease occurrence, factors related to agent, environment and exposure susceptibility. Types of Descriptive Studies: 1- Clinical Studies: A- Case Report: It describes the experience with one case (i.e. one patient). Its aim is: To describe clinical observation in a case with interesting or unusual variation of disease (e.g. atypical presentation). To report results of a new treatment. To report unexpected findings or results of investigation.

Descriptive Studies: B- Case series report: It describes unusual characteristics of a number of similar cases with a given disease, these cases are considered atypical in their presentation or response to treatment. Its aim is: I. To describe variation of a disease. II. It can generate a hypothesis.

Descriptive Studies: 2- Correlation studies: Correlation study uses data of the entire population to compare disease frequency between different groups during the same period of time or at different time periods. It does not use specific samples it uses Records. Its aim is to describe disease morbidity or mortality in relation to e.g. utilization of services, diet consumption, smoking, environmental exposure…etc.

Descriptive Studies: Advantages of Correlation studies: Use already available information It can generate a hypothesis It is Cheap and Quick to perform Disadvantages of correlation studies: It represents averages and not individual values. It is impossible to link exposure with the outcome (disease) in particular individuals. It can not test a hypothesis. It can not control confounding factors.

Descriptive Studies: Uses: 3- Cross Sectional Studies: (Distribution or Prevalence) “It describes the health problem at one point of time where exposure and disease status are assessed at the same time”. i.e. Simultaneous measurement of the Cause and the Effect, and both measurements are related to the same point of time. Uses: It Provides information of disease prevalence. It can evaluate health experiences and programs (vaccination coverage, days lost from work….etc.). It can identify personal demographic characteristics, health related habits, knowledge, attitudes, practices…etc.).

Descriptive Studies: Advantages of Cross Sectional studies: It can detect cases and show the case load (prevalence) It could show the association between exposure and outcome development It could generate a hypothesis Quick and cheap to perform. Disadvantages of Cross Sectional studies: Not useful to describe the load of events (degree of exposure) It deals with survivors only. It does not test hypothesis.

Person:(Age, Sex, Marital Status, and Social Class): Characteristics examined in Descriptive studies: (Person, Place & Time) Person:(Age, Sex, Marital Status, and Social Class): Age: Age distribution of disease shows the following: Certain diseases are more frequent in certain age groups e.g. congenital anomalies during infancy, measles in early childhood, STD in young adults, cancer in old age. This difference among age groups may be due to: - Stage of the Development. - Degree of exposure. - Susceptibility to infection and degree of immunity gained. - Hormonal changes. - Cumulative effect of exposure to a harmful environment.

Characteristics examined in Descriptive studies: (Person, Place & Time) 2. There may be two separate peaks in the age incidence curve of a certain disease (Bimodal) e.g. Leukemia. 3. Patient age my determine the clinical type of a disease. e.g. Cretinism in childhood and Myxoedema in adults. 4. Age can affect the severity of a disease e.g. fracture neck of femur is more serious in the old age, measles more commonly associated with complications in adults rather than children.

Characteristics examined in Descriptive studies: (Person, Place & Time) Sex: Certain diseases are more frequent in males or females (e.g Lung cancer and IHD in males, SLE in females), variation may be due to: Anatomical difference (Cancer prostate in males and cancer cervix in females). Sex linked genetic inheretance (e.g. haemophilia). Hormonal influence (e.g. estrogen protection against IHD in females in the pre-menopausal period). Difference in habits, social relations and other aspect of life style (e.g. males are more prone to chronic bronchitis due to the smoking habits).

Marital Status: Social Class: Characteristics examined in Descriptive studies: (Person, Place & Time) Marital Status: Difference in marital status can affect the nature of a disease: Mental illness are less frequent in married individuals. Breast cancer more frequently affect females who remain single or marry late Social Class: Offspring usually develop the same diseases (e.g. TB, IHD) because they live under the same dietary, social, psychological and environmental influence.

Place: Variation in place distribution of disease may be: Characteristics examined in Descriptive studies: (Person, Place & Time) Place: Variation in place distribution of disease may be: International variation (the pattern of disease is not the same all over the world) National variation (variation of the disease occurrence in the same country) Rural – Urban variation (zoonotic diseases, soil-transmitted diseases and schistosomiasis are more frequent in the Rural areas) Local variation (disease occurrence may be more seen in certain sectors of the city as in slum areas).

Time: Three kind of time trends of fluctuation of disease: Characteristics examined in Descriptive studies: (Person, Place & Time) Time: Three kind of time trends of fluctuation of disease: Short term fluctuation (Epidemics): occurrence of an illness at a community or region with cases in excess of its normal expectation. Periodic fluctuation: Diurnal rhythm, seasonal variation. Long term or secular trends: is the increase or decrease of disease over decades of time.

Thank You BMC2013