Review of Research Designs - Descriptive and Analytical Studies (trans 2) Flashcards
EPIDEMIOLOGY from the Greek words:
Epi – upon
Demos – population
-logy – the study of
It is the study of factors that determine the occurrence and distribution of disease in a population
Two Categories of Epidemiological Studies
1) Descriptive
2. ) Analytic
Two Categories of Epidemiological Studies - Descriptive
activities related to characterizing the distribution of diseases within a population
measures risk, prevalence, and incidence
asks who, where, and when
Two Categories of Epidemiological Studies - Analytic
activities related to identifying possible causes for the occurrence of diseases including:
a) Surveillance
b) Diagnostic testing
c) Natural history of disease
d) Prognostic factors
e) Testing new treatments
Two Types of Research Design
- ) Observational
- Descriptive
a) Case report
b) Case series
c) Cross-sectional
- Analytic
a) Cross-sectional
b) Case-control
c) Cohort - ) Experimental
- Analytic
a) Field trial
b) Clinical Trial
Types of Research Design - CROSS-SECTIONAL STUDY
examines the occurrence of disease (or other health related characteristics) in a defined population at a particular point in time
may involve the measurement of current exposures and/or historical exposures
also used to study prevalence of risk factors and the frequency of prevalent cases of disease for a defined population (hence, sometimes classified as analytic)
the problem with cross-sectional studies, however, is it cannot establish temporality since data on risk factor and outcome is collected at the same time
Reasons for Doing a Cross-Sectional Study
1) To assess burden of disease in a population and to assess need for health services
- e.g. Dr. Tayag and his dance for awareness of metabolic diseases to promote healthy lifestyle
- ordering of drugs as to the demand by the population
2) To compare prevalence of disease in different population
* e.g. Medicines that are popular in Baguio (mostly drugs for iodine deficiency because of lack of seafood and other sources) are different in NCR.
3) To examine trends in disease prevalence or severity over time
* e.g. In the past, cancer and hypertension are considered as diseases of rich people but because of cross-sectional studies, it is proven that they can be manifested by everyone.
Computation in Cross Sectional Study POR (Prevalence Odds Ratio) POR (Prevalence Odds Ratio)
- Chronic diseases (long latency diseases with different follow-up periods for the subjects under observation)
- for regression estimates
- e.g. hypertension, diabetes
PRR (Prevalence Risk Ratio)
- Acute diseases with follow-up periods similar among subjects
- in other applications, we are interested in outcomes which are not strictly ‘diseases’
- duration of symptoms are likely to vary between exposure groups
Types of Research Design - CASE-CONTROL STUDY
a study design in which individuals with an event or condition of interest (CASES) are identified and then compared with regard to one or more exposures to individuals without the event or condition of interest (CONTROLS).
cases and controls need not to be comparable
**Diagram. We start with population at risk. From there, we select cases and controls. Controls are same with cases and the only difference is that controls don’t have the disease. Exposure to specific variables is also asked.
Types of Research Design - CASE-CONTROL STUDY
How is a Case-Control Study Done?
1) Develop a case definition
2) Identify new cases within a specified time period
3) Define and identify appropriate controls
4) Ensure that cases and controls arise from the same population at risk
5) Previous exposure for both cases and controls must be determined
Assessing Exposure in Case-Control Studies
exposure is determined in a retrospective manner, that is one must look back in time to assess exposure status before a person became a case.
e.g. For cancer, the researchers may ask if the subjects had frequent high fiber meals
data collectors must be unaware of whether subject is a case or control
data collectors should be unaware of the study hypothesis
- We tend to be aggressive when we are aware of the hypothesis.
Types of Research Design - CASE-CONTROL STUDY
Computation in Case-Control Study Odds Ratio (OR)
is the odds of exposure given disease divided by the odds of exposure given no disease
OR = ad/bc
Interpretation:
O.R. = 1 then exposure is NOT related to disease
O.R. > 1 then exposure is POSITIVELY related to disease
O.R.
Types of Research Design - CASE-CONTROL STUDY
Biases Usually Associated With Case-Control Studies
- ) Selection Bias
- ) Information Bias
- ) Recall Bias
Types of Research Design - CASE-CONTROL STUDY
Biases Usually Associated With Case-Control Studies - Selection Bias
a distortion in the relationship between exposure and outcome that results from selection of study participants
eg. When doing case-control study on tuberculosis in a hospital, the researchers would usually see severe cases of TB which is not representative of the population of TB cases. Most TB cases are treated at DOTS Facilities.
the relation between exposure and outcome is different for those who participate and those who do not participate but would theoretically be eligible for the study
Types of Research Design - CASE-CONTROL STUDY
Biases Usually Associated With Case-Control Studies - Recall Bias
differential recall of exposure between cases and controls in a study
e.g.Mothers of children with congenital malformations may remember details about possible exposures during pregnancy that mothers without malformations forget.
Types of Research Design - CASE-CONTROL STUDY
Advantages and Disadvantages of Case-Control Study Advantages
1) More economical in time and resources
2) May be used even in rare diseases
Disadvantages
1) Provides only indirect measure of risk
2) More bias of recall of exposure
3) Controls are difficult to assemble
Types of Research Design - COHORT STUDY
an epidemiologic design in which the incidence of a disease (or condition) is compared among exposed and unexposed individuals
Study Population
defines population at risk using inclusion criteria (characteristics that the subject should have in order to be included in the study)
individuals with outcome of interest at time of screening and enrollment ARE NOT eligible for study
sub-clinical presentation of diseases may present challenges in defining the cohort
Types of Research Design - COHORT STUDY
Measuring Exposure
measuring exposure is one of the fundamental activities of a cohort study
exposure measurement must be comparable for all members of the cohort
carefully defined in advance of study
specific attention should be given to the accuracy and precision of proposed measurements
o Pilot studies (small-scale preliminary studies) often needed
Outcome Definition
Primary outcome - main event that will be related to the exposure
o Failure-time outcomes (Death, Disease occurrence)
o Repeated measures (one/more outcome measures) Secondary outcomes - other events that are of interest and may corroborate the findings of the main outcome
Types of Research Design - COHORT STUDY
Potential Biases in Cohort Study
Potential Biases in Cohort Study
1) Detection bias
subjects with exposure are more (or less) closely evaluated for outcome
blinding to exposure status of individual reduces bias
2) Information bias
the quality of information is different between exposed and unexposed subjects
3) Non-response and loss to follow-up
selective loss of exposed (or unexposed) persons
Computation in Cohort Study Relative Risk (RR)
is the incidence of exposed divided by the incidence of unexposed
is a true or absolute measure of risk
Risk difference = [c/(c+d)]-[a/(a+b)]
Types of Research Design - COHORT STUDY
Advantages and Disadvantages of Cohort Study Design Advantages
1) Provides direct estimate of risk and with greater accuracy
2) Less bias of recall or exposure
3) Controls are easier to assemble
Disadvantages
1) More expensive
2) Inefficient, if not impossible, for rare diseases
Types of Research Design - EXPERIMENTAL STUDY
essentially cohort studies except that the groups being studied differ from each other only in the presence of a characteristic or exposure to some factor that is artificially induced
- ) CLINICAL TRIAL
- ) FIELD TRIALS
Types of Research Design:
EXPERIMENTAL STUDY - CLINICAL TRIAL
In clinical trials, patients are enrolled in a study and randomly assigned to one group, either the:
o Intervention group – receives the experimental treatment
o Control group - receives the non-experimental treatment (either placebo or standard method of treatment)
The process mentioned above, the random assignment or allocation of patients into a treatment group is called randomization, and is done especially in clinical trials.
Randomization is different from Random sampling.
o Random sampling is a sampling technique wherein all members of a group have an equal and independent chance of being selected/drawn. Also, random sampling is done before randomization.
o Randomization, esp. in clinical trials, is the process of allocation of subjects into treatment groups; the process of allocation is done by chance, that is, without any ability to predict who will be in which treatment group.
Types of Research Design:
EXPERIMENTAL STUDY - CLINICAL TRIAL
Issues on Clinical Trials
Clinical trial is considered as gold standard for studying interventions, specifically, Randomized Control Trial (RCT). Hence, it is the best study that can provide the strongest of evidence is the RCT.
Biases are only minimized but not totally eliminated.
Strategies employed in clinical trials are randomization and blinding/double-blinding.
Patients in a clinical trial should be given an informed consent. Informed consents satisfy ethical requirements of the study.
Drop-outs are threats to the accomplishment of the study.
Types of Research Design:
EXPERIMENTAL STUDY - FIELD TRIALS
Field trials are similar to clinical trials, except that, interventions in Field trials are preventive rather than of Clinical trials which are therapeutic
Types of Research Design: EXPERIMENTAL STUDY
Computations in Experimental Study Measures of Effect Used in Clinical Trials:
Cure Rate
Risk Ratio, Risk Difference Measures of Effect Used in Field Trials:
Protective value
Risk Ratio, Risk Difference
