Lecture 3
Epidemiological Studies
Dr. Lamya Al-Azzzawi
Types of Epidemiological studies
1.Observational epidemiology 1. Descriptive study a. Case- report, Case
series, and Incidence,
2. Analytical study
a. Cohort study
b. Case control study
2.. Experimental epidemiology
a. Randomized control trials
b. Field trials
c. Community trials
Descriptive study
This type of study considered the first phase of any epidemiological investigation. Descriptive study designs include:
• case reports
• case series
• incidence studies
Case Reports
It generally describes an injury or injuries to one or two individuals that have been identified in a medical situation.
Generally, report a new or unique finding.
• e.g. previous undescribed disease.
• e.g. unexpected link between diseases.
• e.g. unpredicted new therapeutic effect.
Case Series
In a case series, several events are described. These events usually have been observed over a set period (such as one year) and are identified from one reporting source (e.g. a hospital
• Experience of a group of patients with a similar diagnosis.
• Assesses prevalent disease.
• Cases may be identified from a single or multiple sources.
• Generally, report on new/unique condition.
Prevalence or Incidence study
This type of studies commonly used for comparison between two or more or between the same population
Analytical studies
It is most often used to determine the etiology of the disease.
a. Case –control study
b. Cohort study
Case-Control studies represent one form of analytic study that provides information on the relationship between causal factors and injuries
Cases: Diseases
Control: No diseases
Case-Control Study
Strengths
• Less expensive and time consuming
• Efficient for studying rare diseases
Limitations
• Inappropriate when disease outcome for a specific exposure is not known at start of study
• Exposure measurements taken after disease occurrence
• Disease status can influence selection of subjects
• Case control studies provide low cost answers to health questions
Cohort study. This study is conducted on general population that is followed through time to see which members develop the disease. The sequence of cause and effect may be clearly seen in prospective study
Time frame of Studies
Retrospective Study - “to look back”, looks back in time to study events that have previously happened
Study begins here
Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future.
Study begins here
Differences between case –control and Cohort studies
Case- control study
Cohort Study
• Disease has already occurred
• Presence of exposure in cases and controls compared
• Relatively easy to carry out
• Useful for rare cases
• Relatively less costly
• No failures
• Can only have one outcome • Disease is expected to occur in future
• Development of disease in exposed and non-exposed compared
• Time consuming and difficult to carry out.
• Suitable for common disease
• Expensive
• Dropout rate higher
• Can have multiple outcome
Experimental Studies
• investigator can “control” the exposure like laboratory experiments except living populations are the subjects
• generally, involves random assignment to groups
• clinical trials are the most well-known experimental design
• the ultimate step in testing causal hypotheses
• Experimental studies are stronger in determining the etiology of disease than descriptive studies.
• treatment and exposures occur in a “controlled” environment.
• planned research designs.
• Community trials use nonrandom data.
Randomized Controlled Trials (RCTs)
• A design with subjects randomly assigned to “treatment” and “comparison” groups
• Provides most convincing evidence of relationship between exposure and effect
• Not possible to use RCTs to test effects of exposures that are expected to be harmful, for ethical reasons
Randomized Controlled Trials (RCTs)
the “gold standard” of research designs provides most convincing evidence of relationship between exposure and effect.
It is not unexpected to find that observational studies find different results than for clinical trials. For example, there have been 100s of observational studies demonstrating that hormone replacement was protective for women. However, when this was put to a clinical trial, the surprising result was that hormone replacement was not protective
Randomized Controlled Trials
Disadvantages
• Very expensive
• Not appropriate to answer certain types of questions
• it may be unethical, for example, to assign persons to certain treatment or comparison groups
Field Trails (randomized uncontrolled)
1.Preventive trials: It is used to estimate the effect of preventive
techniques
2.Risk factor trials: It is used when specific risk factors are prevented in
groups of populations, like dietary pattern.
Community trials (non-randomized controlled
Such studies are the only way in which a general intervention like fluoridation must be tried out for reducing dental caries. Control communities in the neighborhood can be selected for comparison
Ethical issues
Basic Principles of ethics when practicing epidemiology.
1. All proposals for epidemiological studies should be submitted to institutional ethics committees before start working.
2. Epidemiologist must respect personal privacy and confidentiality always
3. Informed consent must be obtained from participants in studies and they must retain the right to withdraw at any time.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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