Chapter 8 Flashcards
A branch of science that investigates the frequency and distribution of diseases in a defined population in an attempt to determine their causes, to discover ways to alleviate them, and to prevent their reoccurrences
Epidemiology
What is the main feature of epidemiology?
Observe people in their natural setting over a specific period of time, at one point in time, or retrospectively. The objective is to describe specific traits that may be present among members of a population
One group was exposed and the other was not exposed to a variable. Question asks if the exposed group develop a higher incidence of the disease
Risk factors or predictor variables.
-Valuble type of study because it is unethical for researchers to ask patients to do or take something known to be harmful.
T/F Epidemologic studies are considerd observational
True
-Data are collected via surverys, revie, or medical records, etc. and analyzed using statistical tests designed to identify patterns and correlations.
Father of epidemiology. Why?
Dr. John Snow.
-Discovered the cholera epidemic was caused by a contaminated pump. His methods to track and discover this information lead to the foundation of epidemiology
The probability of a person being diagnosed with a disease during a specific period of time (one year usually). The number of newly diagnosed cases of a disease during a specific period of time.
Incidence
I = new cases/population x 100,000
An estimate of the population of an unaffected persons in a population who will develop the disease of interest over a specific period of time.
Risk
-Estimated by observing a population over a defined period of time to determine the number of new cases as compared with the total number of persons.
The proportion of persons in a given population that have a disease at a certain point in time.
Prevalence
-Total number of cases of the disease in a population regardless of when they were diagnosed
P = number of existing cases/population x 100,000
The proportion of a population with a disease at a given point in time
Point prevalence
-May underestimate the frequency of certain conditions
The proportion of a population that has a disease within a defined period of time
Period Prevalence
-Involves repeated monitoring or a population (thus, is better depiction of the overall frequency of a disease)
T/F Incidence and prevalence are sometimes reported as %
True
T/F Prevalence is usually much lower than incidence in short duration diseases like the common cold
True
-Many people contract colds each year, but relatively few people have a cold at one time because the duration is so short
T/F Prevalence in chronic condition is lower than its incidence (type 2 diabetes)
FALSE
Prevalence in chronic conditions is higher than its incidence
-There are 1.2 million new cases of diabetes each year, but once diagnosed, the condition remains and each years incidence is added to the overall prevalence, minus those who die having the condition = 18.2 million.
What key critieria must be met to determine if an exposure to a specific risk factor actually caused a particular disease within a population?
- Temporality
- Consistency
- Dose-response
The exposure must occur prior to the onset of a disease. However, just becuse a given exposure precedes a given disease does not necessarily mean there is a cause-and-effect relationship.
Temporality
-a.k.a. temporal precedence
What are the 4 possible interpretations of temporal relationships?
1) Event A caused Event B
2) Event B caused Event A
3) Both Events A and B were caused by a third related event
4) Neither A or B are related to each other or a third event, but the temporal relationship was merely by chance.
Studies on the relationship carried out by other researchers using different populations get similar results.Need a large number of good quality these to conclude that A caused B
Consistency
Occurs when a greater exposure to a risk factor results in a greater effect on health
Dose-response
-Ex: more cigarettes smoked per day = more likely to get lung cancer
Six additional criteria used to identify cause and effect relationships.
Bradford Hill’s Criteria for Causation
-Keep in mind, none of there can bring indusputable evidence for or against a cause and effect relationship
Bradford Hills Criteria of Causation
1) Strength of Association (stronger the relation, the less likely it was caused by othe factors)
2) Consistency (replication of results by different researchers in different settings)
3) Specificity in the cause (exposure should be associated with a single specific disease)
4) Temporality (exposure must precede the disease)
5) Dose-response relationship
6) Plausibility (Rational scientific basis for the association risk of disease)
7) Coherence (assosication must be consistent with other knowledge on the subject)
8) Experiemental evidence (research that is based on experiments reinforces a causal inference)
9) Analogy (The association is analogous to a known causal relationship)
Which of the following is not true of the epidemologic approach
a) Focus is on prevention rather then treatment
b) Deals with individual populations rather than individual patients
c) Approach is to identify subgroups that are at high-risk of developing a disease and then find out what factors caused it.
d) All of the above are true
d) All of the above are true
T/F
RCTs are always preferred over epidemiologic studies
FALSE
Epidemiologic studies are preferred to RCTs when questions are about diagnosis, prognosis, or causation (related to ethical concerns and feasbility)
Why is there more potential for bias in epidemiologic studies?
- Subjects are not randomly assigned to be en exposure vs. non-exposure groups.
- Differences may exist in the baseline risk of disease between the groups
KEY: Lack of randomization causes increased bias
T/F
The validity of epidemiologic studies depends to a large extent on the reliability of the data that is collected. (usally directly from people or by relying on others; all are potentually unreliable sources)
True
What are the 3 most common designs used in epidemiologic research?
- Cross-sectional studies
- Case-control studies
- Cohort studies
(Which one to use depends on the frequency of the disease or condition and the availability of human and economic resources)
Assesses the health status and exposure levels of persons in a population at one point in time. Cases must be actively manifest the disease to be included. Cases with developing conditions that have not yet been diagnosed are not counted.
Cross-sectional studies
-a.k.a. prevalence studies
What is the purpose of a cross sectional study?
To determine if there is an association between a suspected causal factor and a condition.
-Useful to discover associations, but incapable of determining if one factor caused the other
T/F
Case-control or cohort studies are often used to verify the results of cross-sectional studies
True
Why are cross-sectional studies attractive to researachers?
- Quick and easy to carry out
- Inexpensive
(May require a long time to gather all of the required information)
Often inital research tools used to investigate exposures to risk factors and their relationshipst to disease
Cross-sectional study
A study that starts off by identifying two groups of subjects (one has a disease or condition, the other is free from disease). Prior experiences of the cases are compared with those of the controls to see if the exposures influences the odds of developing the disease
Case-control studies
T/F
Subjects in case-control studies should be as similar to cases as possible regarding age, gender, weight, occupation, etc. except for the presence of the disease
True
What is one flaw with a case control study?
They are retrospective so they can not determine the risk of developing a disease
-Can estimate the odds of developing a disease given that a person was exposed to a risk factor (Odds Ratio, OR)
The ratio of the odds of developing the disease in the exposed group divided by the odds of developing the disease in the unexposed group
Odds Ration (OR)
T/F
An OR of 1 implies there is increased risk to a condition or disease in the exposed group compare to the unexposed group
FALSE
OR = 1 = risk is equal in exposed and unexposed group
OR = >1 = risk is increased in exposed group
OR = <1 = exposure reduces the disease risk (protective)
What is the main disadvantage in case-control studies?
Design is vulnerable to many biases because cases and controls are selected after the disese outcome and exposure have occured
Bias caused by systematic differences between the way cases and controls recall past exposures
Recall bias
Bias. In a hospital setting, cases and controls are systematically different from each other related to cases being more prone to hospital admission simply because they have a higher rate of exposure and incidence of the disease (a type of selection bias)
Berkson’s bias
-a.k.a. Berkson’s bias
What type of study is the best way to study rare diseases?
Case-control studies
-Definitive prospective studies typically require many subjects, which is not feasible if the disease is rare. It is much easier to select a group of subjects who already have a rare disease and then look back into their histories for clues
The effect each of the independent variable on the outcome is analyzed separatley. Commonly used to distinguish confounding variables from true exposure-disease associations.
Stratified analysis
Studies that follow groups of subjects forward in time and compare their outcomes. One group is exposed to a known or suspected cause of disease with the other group is not.
Cohort studies
-a.k.a. longitudinal studies
What is the objectives of doing outcome measures on both groups in a cohort study?
To determine if there are differences of diseases occurence between the groups
What is the major advantage of cohort studies over case-control studies?
Cohorts are able to establish the temporal precedence of an exposure in relation to health outcome (satisfying one of the main prereqs in determining causation)
-Much less subject to bias as well.
T/F
Cohort studies have the best design to determine risk of a harmful substance
True
-still considered observational because random assignment to groups is not used
T/F
RCTs are usually easier to administer and less costly then Cohort studies. RCTs are more acceptable than Cohort studies from an ethical perspective as well.
FALSE
Cohorts are better than RCTs for those reasons (potentially harmful treatments are not utilized and treatment is not withhelf from one of the groups)
Calculated from cohort studies. The probability of disease in the exposed group, divided by the probability of disease in the unexposed group.
Relative Risk (RR)
T/F
If the RR >1, the association is postive while an RR <1 means there is a negative or protective association.
True
The probability of disease in the exposed group minus the probability of disease in the unexposed group. Represents the excess risk due to exposure to the factor under investigation.
Attributable risk (AR)
Used mainly in RCTs. Is the difference in the probability of disease between the treatment and control groups.
Attributable risk reduction (ARR)
-Same formula as AR
The comparative reduction in rates of bad outcomes between the experimental and control groups. Commonly reported, but not a very good way to compare outcomes.
Relative risk reduction (RRR)
The number of patients who need to be treated in order to prevent one additional bad outcome
Number needed to treat (NNT)
-Perfect is 1
Involve one group of subjects who have some factor in common. Regularly evaluated to monitor the evolution of the disease.
Single group cohort studies.
-a.k.a. longitudinal studies or inception cohort studies.
Best utilized with common diseases. Not feasible with rare conditions. The potential for bias is less compared to other epidemiologic studies.
Cohort designs
T/F
RR should be used with cohort studies while OR should be used with case-control studies.
True
