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Presented at CRC course KFMC on January 26, 2020 11-12am by Prof Omar Hasan Kasule Sr Professor of Epidemiology and Bioethics, King Fahad Medical City.
TYPES OF OBSERVATIONAL STUDIES
• Cross-sectional: picture of disease and cause at a point in time
• Case-control: compare the cause in cases (have the disease) and controls (have no disease)
• Cohort/follow-up studies (follow up in the future 2 groups: with and without cause to see the occurrence of disease).
ADVANTAGES OF OBSERVATIONAL STUDIES
• Low cost
• Fewer ethical issues
DISADVANTAGES OF OBSERVATIONAL STUDIES
• Disease etiology is not studied directly because the investigator does not manipulate the exposures
• Unavailability of information
• Confounding
SOURCES OF SECONDARY DATA 1
• Secondary data is from decennial censuses, vital statistics, routinely collected data, epidemiological studies, and special health surveys.
• Census data is reliable. It is wide in scope covering demographic, social, economic, and health information. The census describes population composition by sex, race/ethnicity, residence, marriage, socio-economic indicators.
• Vital events are births, deaths, Marriage & Divorce, and some disease conditions.
SOURCES OF SECONDARY DATA 2
• Routinely collected data are cheap but may be unavailable or incomplete. They are obtained from medical facilities, life and health insurance companies, institutions (like prisons, army, schools), disease registries, and administrative records.
• Observational epidemiological studies are of 3 types: cross-sectional, case-control, and follow-up/cohort studies.
• Special surveys cover a larger population than epidemiological studies and maybe health, nutritional, or socio-demographic surveys.
PRIMARY DATA COLLECTION BY QUESTIONNAIRE 1
• Questionnaire design involves content, the wording of questions, format, and layout.
• The reliability and validity of the questionnaire as well as practical logistics should be tested during the pilot study.
• Informed consent and confidentiality must be respected.
• A protocol sets out data collection procedures.
PRIMARY DATA COLLECTION BY QUESTIONNAIRE 2
• Questionnaire administration by face-to-face interview is the best but is expensive.
• Questionnaire administration by telephone is cheaper.
• Questionnaire administration by mail is very cheap but has a lower response rate.
• computer-administered questionnaire is associated with more honest responses.
PHYSICAL PRIMARY DATA COLLECTION 1
• Data can be obtained by clinical examination, standardized psychological/psychiatric evaluation, measurement of environmental or occupational exposure, and an assay of biological specimens (endobiotic or xenobiotic) and laboratory experiments.
• Pharmacological experiments involve bioassay, quantal dose-effect curves, dose-response curves, and studies of drug elimination.
• Physiology experiments involve measurements of parameters of the various body systems.
PHYSICAL PRIMARY DATA COLLECTION 2
• Microbiology experiments involve bacterial counts, immunoassays, and serological assays.
• Biochemical experiments involve measurements of concentrations of various substances.
• Statistical and graphical techniques are used to display and summarize this data.
EXAMPLE OF OBSERVATIONAL STUDY 1
EXAMPLE OF OBSERVATIONAL STUDY 2
EXAMPLE OF OBSERVATIONAL STUDY 3
EXAMPLE OF OBSERVATIONAL STUDY 4
EXAMPLE OF OBSERVATIONAL STUDY 5