Preventive Medicine: Epidemiology 4

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Questions and Answers

According to the Tobacco Institute, what is the relationship between smoking and diseases?

Smoking is a cause of a variety of diseases

Smoking prevents diseases

Smoking is a risk factor, but not a cause, of a variety of diseases (correct)

Smoking has no correlation with diseases

What type of cause is characterized by always leading to a disease if present?

Risk factor

Sufficient cause (correct)

Conditional cause

Necessary cause

What is the relationship between smoking and bronchogenic lung cancer?

Smoking is a risk factor, but not a sufficient cause, of bronchogenic lung cancer (correct)

Smoking has no correlation with bronchogenic lung cancer

Smoking is a necessary cause of bronchogenic lung cancer

Smoking is a sufficient cause of bronchogenic lung cancer

What is the purpose of epidemiologists interpreting statistical associations between a disease and an exposure?

To decide if the associations are artifactual, noncausal, or causal Signup and view all the answers

What is the order of decreasing strength of the three fundamental types of causes?

Sufficient cause, risk factor, necessary cause Signup and view all the answers

What is an example of a sufficient cause in the context of genetic abnormalities?

Homozygous genetic abnormalities leading to a fatal disease Signup and view all the answers

Why is it unknown whether all smokers would eventually develop lung cancer if they continued smoking and lived long enough?

Because the human life span is not long enough to observe the effect Signup and view all the answers

What is the key aspect of the association between the placement of new outlets and the movement of new consumers into neighborhoods with dense fast food?

It is a bidirectional effect Signup and view all the answers

What is the first step in determining causation in epidemiologic investigation?

Investigation of the statistical association Signup and view all the answers

What is the purpose of testing hypotheses about risk factors or protective factors?

To determine the statistical association Signup and view all the answers

What is required for a presumed risk factor to be considered causal?

It must be present significantly more often in persons with the disease than in persons without the disease Signup and view all the answers

What is the equivalent early step in a murder investigation compared to an epidemiologic study?

Showing a geographic and temporal association between the murderer and the victim Signup and view all the answers

What was the result of the earliest epidemiologic studies on smoking and lung cancer?

Smokers had an average overall death rate approximately two times that of nonsmokers Signup and view all the answers

What is the purpose of research design in epidemiologic studies?

To allow a statistical association to be shown, if it exists Signup and view all the answers

What is the relationship between statistical analysis and research design?

They work together closely Signup and view all the answers

What is the limitation of statistical association in determining causation?

It does not prove causation Signup and view all the answers

What is the final step in determining causation in epidemiologic investigation?

Elimination of all known alternative explanations Signup and view all the answers

What is the probability of an unlikely event occurring by chance alone?

1 in 20 Signup and view all the answers

What is the term used to describe intermediary factors in a causal pathway?

Intervening variables Signup and view all the answers

What is the term used to describe a direct causal association?

Direct causal association Signup and view all the answers

What is the principle of data analysis that states that association does not prove causation?

Association does not prove causation Signup and view all the answers

Why is it unlikely that quitting smoking causes lung cancer?

Because smokers with undetectable lung cancer stop smoking and feel better temporarily Signup and view all the answers

What is bidirectional causation?

Each of two variables reciprocally influencing the other Signup and view all the answers

What is the role of intervening variables in a causal pathway?

They influence the effect through other factors Signup and view all the answers

Why is baldness not likely a cause of coronary artery disease?

Because both baldness and coronary artery disease are functions of age, gender, and dihydrotestosterone level Signup and view all the answers

What is the difference between a direct and indirect causal association?

A direct causal association occurs without intermediary factors, while an indirect causal association occurs through intermediary factors Signup and view all the answers

What is the importance of considering the temporal relationship in a causal association?

It is important in determining the direction of causation Signup and view all the answers

What is a necessary cause in the context of disease?

A factor that must be present for disease to occur Signup and view all the answers

Which of the following is an example of a necessary cause?

Mycobacterium tuberculosis for tuberculosis Signup and view all the answers

What is a risk factor in the context of disease?

A factor that increases the probability of disease Signup and view all the answers

Which of the following is an example of a risk factor?

Cigarette smoking for lung cancer Signup and view all the answers

What is a sufficient cause in the context of disease?

A factor that always results in disease Signup and view all the answers

What is the main difference between a necessary cause and a sufficient cause?

A necessary cause may not result in disease, while a sufficient cause always results in disease Signup and view all the answers

What is required for a causal relationship to exist?

A statistically significant association between the outcome and the presumed cause Signup and view all the answers

What is the difference between a directly causal association and an indirectly causal association?

A directly causal association exerts its effect in the absence of intermediary factors, while an indirectly causal association exerts its effect through intermediary factors Signup and view all the answers

What is a noncausal association?

A relationship between two variables where the temporal relationship is incorrect Signup and view all the answers

Why is it necessary to establish a statistically significant association between the outcome and the presumed cause?

To rule out random variation as a possible explanation Signup and view all the answers

What is one of the key challenges in determining cause and effect in research design?

Determining the temporal sequence of events Signup and view all the answers

What is the main purpose of eliminating alternative explanations in research?

To rule out other plausible explanations for the observed association Signup and view all the answers

Why is randomization important in epidemiologic investigations?

To reduce the risk of bias in participant allocation Signup and view all the answers

What is the main difference between a murder investigation and an epidemiologic investigation?

The goal of the investigation Signup and view all the answers

Why is it impossible to fully eliminate all alternative explanations in epidemiologic investigations?

Because new explanations can always be proposed Signup and view all the answers

What is the main advantage of proper research design in epidemiologic investigations?

Reducing the likelihood of competing causal explanations Signup and view all the answers

What is an example of a disease where the understanding of its causation has changed over time?

All of the above Signup and view all the answers

Why is it important to consider alternative explanations in epidemiologic investigations?

To eliminate competing explanations for the observed association Signup and view all the answers

What is the main challenge in establishing cause and effect relationships in epidemiologic investigations?

Eliminating alternative explanations Signup and view all the answers

What is the primary reason why an association may seem causal when it is not?

Presence of an infectious agent Signup and view all the answers

What are the four possible explanations for a statistically significant association?

True causal association, chance, random error, and systematic error Signup and view all the answers

What is the main criterion to establish a causal relationship between a risk factor and a disease?

All of the above Signup and view all the answers

What is the primary challenge in proving the temporal relationship between a risk factor and a chronic disease?

All of the above Signup and view all the answers

What was the original theory behind the prediction of cholera rates in 1849?

Miasma theory Signup and view all the answers

What is the purpose of the criteria for a statistically significant association to be causal?

To increase the probability of a true causal association Signup and view all the answers

What was the actual reason for the association between cholera infection and elevation?

Wells were more likely to be infected by polluted river water at low elevations Signup and view all the answers

What is an example of a vicious cycle in a chronic disease?

Obesity causing osteoarthritis, which leads to inactivity that worsens obesity Signup and view all the answers

What is the current widely accepted theory of cholera transmission?

Germ theory Signup and view all the answers

What is the purpose of randomization in establishing a causal relationship?

To provide experimental control Signup and view all the answers

What is the traditional view of the causes of coronary heart disease?

Hyperlipidemia, hypertension, and smoking Signup and view all the answers

What is a common misconception about the relationship between a risk factor and a disease?

Assuming a causal relationship when there is only an association Signup and view all the answers

What was the alternative explanation for coronary heart disease in the past?

Excess levels of iron in the body Signup and view all the answers

What is the role of biologic plausibility in establishing a causal relationship?

To provide evidence for the association making sense based on the natural history of the disease Signup and view all the answers

What is the relationship between chronic inflammation and coronary heart disease?

Chronic inflammation is a cause of coronary heart disease Signup and view all the answers

What is an example of an association that shows a dose-response relationship?

The relationship between cigarette smoking and lung cancer Signup and view all the answers

What was the result of the randomized controlled clinical trial of antibiotic treatment for C.pneumoniae infection?

Treatment with roxithromycin reduced the number of cardiac events Signup and view all the answers

What is a potential factor in the development of atherosclerosis-like arterial disease?

Herpesvirus infection Signup and view all the answers

What is bias in epidemiologic research?

A differential error that produces findings consistently distorted in one direction Signup and view all the answers

What is the first step in a clinical trial?

Assembling the groups of participants to be studied Signup and view all the answers

What is confounding?

The confusion of two supposedly causal variables Signup and view all the answers

What is the purpose of categorizing biases in terms of assembly bias or detection bias?

To identify sources of bias in research Signup and view all the answers

What is synergism?

The interaction of two or more variables producing a greater effect than their individual effects Signup and view all the answers

What is effect modification?

The phenomenon in which a third variable alters the direction or strength of association between two other variables Signup and view all the answers

What is random error?

A nondifferential error that produces findings too high and too low in approximately equal frequency Signup and view all the answers

What is the consequence of bias in epidemiologic research?

It produces a false association Signup and view all the answers

What is the consequence of allowing participants to select their own study groups in a clinical trial?

Selection bias Signup and view all the answers

What type of bias can occur if investigators choose a nonrandom method of assigning participants to study groups?

Allocation bias Signup and view all the answers

Why may the results of a study lack external validity?

Due to self-selection of participants Signup and view all the answers

What is a potential problem with the randomization process in clinical trials?

It can be bypassed by staff Signup and view all the answers

Why may patients with terminal diseases be more likely to participate in a new treatment study?

Because they have little to lose Signup and view all the answers

What can occur if a randomization process is not followed, and participants are not truly randomized?

Allocation bias Signup and view all the answers

What is a consequence of self-selection into a study?

Lack of generalizability Signup and view all the answers

Why may it be difficult to generalize the results of a study to the broader population?

Due to self-selection of participants Signup and view all the answers

What can occur when participants are allowed to choose their own study groups?

Selection bias Signup and view all the answers

What is a potential limitation of a study that allows participants to select their own study groups?

Lack of external validity Signup and view all the answers

Why is it important to ensure that the differences observed in the study groups are not attributable to measurement bias or recall bias?

To ensure the differences observed are real and not due to bias Signup and view all the answers

What is an example of measurement bias?

Both a and b Signup and view all the answers

What is detection bias?

Bias that occurs when the investigators fail to detect a case of disease, a possible causal factor, or an outcome of interest Signup and view all the answers

What can occur if two groups of study subjects have large differences in their rates of loss to follow-up?

Detection bias Signup and view all the answers

What can occur if the investigators drop participants with poor compliance from the study group?

Selection bias Signup and view all the answers

What type of bias can occur if some investigators or study sites have blood pressure cuffs that measure incorrectly?

Measurement bias Signup and view all the answers

Why is it important to obtain the normal standards for each laboratory when collecting laboratory data?

To correct for measurement bias Signup and view all the answers

What type of bias occurs when people who have experienced an adverse event are more likely to recall previous risk factors?

Recall bias Signup and view all the answers

What is the result of random error in a study?

Findings that are too high and too low in approximately equal amounts Signup and view all the answers

What is confounding in the context of research?

The confusion of two supposedly causal variables Signup and view all the answers

What is an example of confounding in research?

The association between gray hair and myocardial infarction Signup and view all the answers

What is the result of negative confounding?

A true association is masked or weakened Signup and view all the answers

What is the result of positive confounding?

A false association is created Signup and view all the answers

Why is it important to consider confounding in research?

To identify true associations between variables Signup and view all the answers

What is the effect of age on educational success in teenage mothers?

Age is negatively associated with educational success Signup and view all the answers

What is the term used to describe the interaction of two or more variables, so that the combined effect is clearly greater than the sum of the individual effects?

Synergism Signup and view all the answers

What is the term used to describe the situation where the direction or strength of an association between two variables differs according to the value of a third variable?

Effect modification Signup and view all the answers

What is an example of a risk factor that increases the risk for several different diseases?

Cigarette smoking Signup and view all the answers

What is the term used to describe a situation where a single factor increases the risk for several different diseases?

Risk factor Signup and view all the answers

What is the purpose of identifying effect modification or interaction?

To understand the underlying biological mechanisms Signup and view all the answers

What is an example of a disease where the understanding of its causation has changed over time?

Burkitt's lymphoma Signup and view all the answers

What is the term used to describe the interaction of two or more variables, where the combined effect is less than the sum of the individual effects?

Antagonism Signup and view all the answers

What is the term used to describe the situation where a single disease has several different causal factors?

Multifactorial disease Signup and view all the answers

What is the purpose of considering the temporal relationship in a causal association?

To establish causality Signup and view all the answers

What is the term used to describe the situation where a third variable causes the reversal of direction of effect?

Qualitative confounding Signup and view all the answers

What is a major challenge in determining the causal contribution of a factor to a disease?

Controlling for age and other confounding variables Signup and view all the answers

What is the purpose of epidemiologists in determining the causes of disease?

To discover the causes of disease in the environment, nutrition, lifestyle, and genes of individuals and populations Signup and view all the answers

What is the key aspect of the relationship between age and myocardial infarction?

Age is a confounder in the relationship between cholesterol and myocardial infarction Signup and view all the answers

What is the purpose of statistical analysis in epidemiologic studies?

To control for confounding variables Signup and view all the answers

What is a necessary cause of a disease?

A factor that always leads to a disease if present Signup and view all the answers

What is the main challenge in establishing a causal relationship between a risk factor and a disease?

All of the above Signup and view all the answers

What is the primary criterion for establishing a causal relationship between a factor and a disease?

The absence of alternative explanations Signup and view all the answers

What is the main difference between a necessary cause and a sufficient cause of a disease?

A necessary cause is a factor that always leads to a disease, while a sufficient cause is a factor that sometimes leads to a disease Signup and view all the answers

Study Notes

Causation and Risk Factors

In epidemiology, determining causation is a challenging task that requires careful interpretation of statistical associations.
There are three types of causal relationships:
- Sufficient cause: The factor (cause) always leads to the effect (disease). Rare examples include certain genetic abnormalities.
- Necessary cause: The factor must be present for the effect to occur, but its presence does not guarantee the effect. Example: Mycobacterium tuberculosis for tuberculosis.
- Risk factor: An exposure, behavior, or attribute that increases the probability of a disease. Examples: smoking, high blood pressure.

Types of Associations

Directly causal association: The factor exerts its effect without intermediary factors. Example: A severe blow to the head causing brain damage.
Indirectly causal association: The factor influences other factors through intermediary variables. Example: Poverty leading to poor health and death through inadequate nutrition, housing, and medical care.
Noncausal association: A statistical association without a causal relationship. Example: Quitting smoking associated with increased lung cancer incidence, but the cancer started before quitting.

Steps in Determining Cause and Effect

Investigation of statistical association: Show a statistically significant difference in disease rates between exposed and non-exposed groups.
Investigation of temporal relationship: The presumed causal factor must occur before the effect (disease).
Elimination of all known alternative explanations: Rule out other possible explanations for the association.

Criteria for Causal Association

Strength: The difference in disease rates between exposed and non-exposed groups is large.
Consistency: The association is always observed when the risk factor is present.
Specificity: The association is not observed when the risk factor is absent.
Biologic plausibility: The association is biologically plausible based on current knowledge.
Dose-response relationship: The risk of disease increases with stronger exposure to the risk factor.

Importance of Research Design

A well-designed study can help establish causal relationships by controlling for confounding variables and allowing for causal inferences.
Experimental studies can establish temporal relationships and eliminate alternative explanations.### Randomization in Research
Randomization ensures that neither self-selection nor investigator bias influences the allocation of participants into treatment and control groups
Randomization helps to make the treatment and control groups comparable with regard to disease susceptibility and severity

Limitations of Scientific Explanations

Scientific explanations are always tentative, even when they seem perfectly satisfactory and meet the criteria for statistical association, timing, and elimination of known alternatives
New explanations can emerge and challenge existing theories, making it impossible to fully eliminate alternative explanations

Historical Examples of Challenged Theories

Cholera

In 1849, the "miasma theory" was used to predict cholera rates in London, which showed an accurate correlation between predicted and observed rates
The true reason for the association was later found to be the contamination of wells by polluted water from the Thames River, not "miasmas" (noxious vapors)

Coronary Heart Disease

The reigning paradigm of coronary heart disease attributes it to hyperlipidemia, hypertension, and smoking
Alternative explanations have been proposed, including excess levels of iron in the body, chronic inflammation from infections, and others
Some studies have implicated chronic inflammation from infections in developing coronary heart disease, including atherosclerosis-like arterial disease in infected chickens
Antibiotic treatment has been shown to reduce cardiac events in patients with coronary artery disease, but not all studies have found this effect

Common Pitfalls in Causal Research

Bias:
- A differential error that produces findings consistently distorted in one direction due to nonrandom factors
- Can weaken a true association, produce a false association, or distort the direction of the association between variables
Types of bias:
- Assembly bias:
  - Occurs during the assembly of groups in a clinical trial
  - Results from non-comparable groups at the start of the trial
- Selection bias:
  - Occurs when participants are allowed to select their own study group
  - Results in differences among subjects rather than the effect of the intervention
- Allocation bias:
  - Occurs when non-random methods are used to assign participants to study groups
  - Can result from faulty randomization processes
Associated problems of validity:
- Internal validity: presumed for participants in the study
- External validity: unclear for the general population due to self-selection of participants
Example:
- Polio vaccine trials (1954): socioeconomic status affected participation and results

Detection Bias

Types of detection bias:
- Measurement bias:
  - Results from incorrect measurements (e.g., height with shoes on)
  - Can be corrected by obtaining normal standards for each laboratory
- Recall bias:
  - Results from differences in recall between groups (e.g., mothers of abnormal infants)
  - Can produce spurious associations

Random Error

A nondifferential error that produces findings too high and too low in approximately equal amounts
Decreases the probability of finding a real association by reducing statistical power

Confounding

The confusion of two supposedly causal variables
Can obscure a true causal relationship
Example:
- Age and gray hairs associated with myocardial infarction, but age itself increases both gray hairs and risk of myocardial infarction

Synergism

The interaction of two or more presumably causal variables, resulting in a combined effect greater than the sum of individual effects
Example:
- Asbestos and cigarette smoking increase the risk of lung cancer more than either factor alone

Effect Modification (Interaction)

The direction or strength of an association between two variables differs according to the value of a third variable
Example:
- Epstein-Barr virus infection manifests differently in different geographic areas
- Gender modifies the effect of age on blood pressure

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Description

Learn about the challenging task of determining causation in epidemiology, including types of causal relationships such as sufficient and necessary causes.