Lecture 6 Flashcards
Epidemiologic
(population health &
clinical)
Studies can be split into two groups
Observational and
experimental
Observational Studies can be split into two groups
Descriptive
Analytic
Descriptive Studies
Case Reports
Case Series
Ecological
Cross-Sectional
Analytic Studies
-Ecological
-Cross-sectional
-Case-Control
Cohort
Experimental Studies can be split into two groups
Randomized controlled trial
Community trial
Descriptive health research
No hypothesis
Not looking to prove or disprove anything
1. To monitor the public’s health
2. To evaluate the success of
intervention programs
3. To generate hypotheses about causes of disease
Analytic
Evaluate hypothesis about the causes of disease
To evaluate the success of
intervention programs
Components of a Study
- Population
- Exposure
- Outcome
- Potential Confounders
- Analysis
- Communication of Findings
Differences between Selection bias and Generalizability/external validity (ON EXAM)
Selection bias is a flaw in the sampling process that can affect the validity of study results even within the sample itself.
Generalizability is about how well the results of the study can be applied beyond the study sample.
Exposure
Determinant of interest upon which an outcome depends;
can be constitutional, environmental, or behavioral
➢ Genetic polymorphism, female sex, short stature
➢ Fluoridated water, air pollution, passive cigarette smoke
➢ Cigarette smoker, fitness enthusiast, high fiber diet
The goal of knowing exposures
to minimize errors
Potential Confounders
Extraneous risk factor for an outcome;
can be constitutional, environmental, or behavioral
Analysis
examination of your study data;
estimation of measures of disease frequency and association
Communication of Findings
Tell the appropriate persons or community
what you found even if you found no association
examples
➢Peer-reviewed journals
➢Conferences and meetings
➢Government reports
➢What about popular and social media?
Hierarchy of evidence from least to highest
In vitro (test tube research)
Animal research
Ideas, editorial, opinions
Case reports
Case series
Case control studies
Cohort studies
Randomized controlled double blind studies
Systemic Reviews and meta analysis
What kind of evidence is good for formulating research questions, theory generating
Ideas, editorial, opinions
Case reports
Case series
What kind of evidence is used in most health research
Case control studies
Cohort studies
Randomized controlled double blind studies
Systemic Reviews and meta analysis
Evidence that is a good starting point more in the domain of biology
In vitro (test tube research)
Animal research
There is no good or bad TYPE of design but
poorly vs. properly conducted studies
Case report:
a report of a health issues in one patient, A disease, a disorder, or undergoing a procedure
Case series:
a report that describes a group of individuals who have the same health issue
The history of AIDS
Was identified in SanFran
(Was everywhere in the world)
Very rare type of skin cancer caused by immune deficiency
Was originally thought to be related to homosexuality due to discrimination
Case Report and Case Series
No theory, no research question, goal is not researching, only reporting
Often done by clinicians. They do not want to prove a theory only wish to report.
➢ May generate ideas for research questions
The main scientific part of Case report and case series:
defining the case
Sign vs Symptom
Sign: an objective indication of disease that can be clinically observed, such as a rash, cough, fever, or elevated blood pressure
Symptom: a subjective indication of illness that is experienced by an individual but cannot be directly
observed by others
Several coding systems
➢ International Classification of Diseases (ICD)
➢ Diagnostic and Statistical Manual of Mental Disorders (DSM)
Case Report and Case Series
➢ Mostly in medical settings but data collection usually
with standard questionnaires
➢ Ethical issues should be respected
➢ Privacy
➢ Sometimes a group will be labeled unjustly because of the
original case series
➢ Few or no data analysis is required
➢ Clinical discussion dominates the report
Types of Analytic
Studies
Experimental
Observational
Experimental
Investigator actively
manipulates which
groups receive
agent under study
-Clinical Trial
-Community Trial
Observational
Investigator
observes as nature
takes its course
-Cross-sectional
-Cohort Study
-Case-Control Study
Differences btwn Observational and experimental
Data: Collect vs Create
Exposure assessment:
Inquiry vs Random Assignment
Outcome assessment
Inquiry vs Inquiry
Analysis of the
association
Depends, …. vs Complex but more
straightforward
In cohort studies you call this formula (a / (a+b)) / (c / (c+d))
relative risk
In cross sectional study you call the same formula, as the relative risk formula in cohort studies a: (refer to slides if you are confused)
prevalence ratio
In prevalence ratio formula(a / (a+b)) / (c / (c+d))
high is over the low
Limitations of Cross-sectional Studies
Because a cross-sectional study has no time dimension, it cannot be used to assess causality
In cross sectional study An exposure can be said to be “associated” or “related” to a disease,
but a cross-sectional
study cannot show that an exposure caused a disease
Repeated cross-sectional study:
a series of cross-sectional studies that re-sample and re-survey representatives from the same source population at two or more different time points
> does not track the same New set of participants is sampled from the source population for each round of data
collection
Correlational Studies
In these studies, the unit of analysis is the group, not the
individual. The group, or ecological unit, represents an
aggregate of individuals
Terminology:
➢ Correlational studies
➢ Ecological studies
➢ Aggregate studies
The same
Ecological Fallacy
The incorrect assumption that individuals follow the trends observed in population-level
data, not a methodological error or bias
> The experience of individuals in a population may vary significantly from the
population average
