Measures of Disease Frequency in Epidemiology

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What is the main focus of epidemiology?

Studying the frequency and distribution of health-related states and events in human populations

Which population type is defined by being in or out of a state?

Dynamic population

What does a proportion involve dividing by?

The sum of itself with another quantity

What does a rate measure in epidemiology?

The occurrence of an event per population

How is ratio different from proportion in epidemiology?

Proportion involves dividing by another quantity, while ratio divides one quantity by another

What does prevalence measure?

How much disease is present in a population

When is point prevalence calculated?

At a specific moment in time

What is period prevalence?

A proportion within a range of time

What is not useful for determining what caused the disease?


Why is prevalence information relevant for health service planning?

To assess the burden of disease in populations

Which measure is more accurate for exploring causes of a disease?

Incidence Rate

What does the Cumulative Incidence measure?

New cases of a disease divided by the population at risk

Why is Cumulative Incidence less accurate than Incidence Rate?

It requires complete follow-up for all subjects

Which population type is Incidence Rate more useful for?

Dynamic populations

What does Person-Time Rate involve?

Accrual of total time in which subjects were at risk

If incidence and cure rates are steady while treatment prolongs the life of individuals with a disease, what is the expected impact on prevalence?


In a fixed population with steady incidence and death rates, what happens to prevalence if the treatment cures the disease?


What does the Mortality Rate measure?

Proportion of deaths from a disease over total population

Which rate is calculated as the proportion of cases of a disease without deaths divided by the total population?

Morbidity Rate

What does the Attack Rate measure?

Proportion of exposed people developing a disease

What is the purpose of Measures of Association in epidemiology?

To determine the relationship between a disease and potential risk factors

What is the Prevalence Ratio used for in epidemiological studies?

To calculate the ratio of prevalence between exposed and unexposed groups

In a 2x2 Table for Summarizing Epidemiological Data, what is typically compared?

Whether or not people have the disease with whether or not people are exposed to a specific risk factor

What does the Prevalence Ratio value of 2.85 indicate?

There is a higher prevalence of the disease in the exposed group compared to the unexposed group

What aspect of groups is compared when using Measures of Association?

Exposure or characteristic

What does a Rate Ratio (RR) less than 1.0 indicate?

Negative association

In epidemiological terms, what does a Rate Difference (RD) of 0 imply?

No association between exposure and disease

If the Rate Ratio (RR) is near 1.0, what does this suggest about the association?

Weak association

What does it signify if a Rate Difference (RD) is greater than 0?

Positive association

How is the Rate Ratio (RR) different from the Rate Difference (RD)?

RR measures strength of association, while RD measures public health impact

What does a Rate Difference (RD) less than 0 signify?

Negative association

What is the main purpose of Descriptive Studies in epidemiology?

Generating hypotheses

In Descriptive Studies, what is a major limitation that affects the ability to establish causal relationships?

Inherent limitations in study design

Which type of study design follows the results as they develop from present time forward?

Prospective Studies

What is a key advantage of Case Reports in epidemiology?

Ease in generating a hypothesis

When considering Individual studies, what is a significant disadvantage of Case Reports?

They can't test a hypothesis

What is a key advantage of a Case Series compared to Case Reports?

Provides more evidence for hypotheses

In a Cross-Sectional Study, what is a common limitation that makes it hard to establish causality?

Hard to determine relationship between cause and effect

What is a significant advantage of a Repeated Cross Sectional Study over a simple Cross-Sectional Study?

Observes the same population at different moments in time

Which of the following is NOT an advantage of a Cross-Sectional Study?

Can establish causal relationships

What is a primary disadvantage of a Case Series in terms of hypothesis testing?

Cannot test a hypothesis

Which of the following is an important use of a Cross-Sectional Study in epidemiology?

Monitoring health status in a population

What is a primary disadvantage of an Ecological Study?

Tries to create facts about individuals through group results

Why is it challenging to establish causality in an Ecological Study?

It looks at aggregate data rather than individual-level data

Which factor makes Ecological Studies susceptible to inaccurate associations?

Uses aggregate data from a whole population

What is a significant limitation of Ecological Studies in terms of association establishment?

Dependence on group-level data rather than individual data

Why do Ecological Studies struggle to ensure the exposure and disease development are linked in the same person?

Inability to track individual-level information in aggregate analysis

What type of study is indicated for diseases that take a long time to develop?

Retrospective Study

What measure can be used to assess the strength of the association between an exposed cohort and an unexposed cohort in a Longitudinal Study?

Relative Risk (RR)

Which type of Cohort Study involves exposure occurring before the disease and compares the disease development over time between exposed and unexposed cohorts?

Prospective Study

What is a common characteristic of Longitudinal Studies that makes them advantageous for certain types of diseases?

Exposure preceding disease development

Which characteristic of Ambi-Directional Studies makes them vulnerable to bias and limits their internal validity?

Prospective and retrospective aspects

What is an advantage of Cohort Studies when used to study multiple effects of exposure?

Can establish causality

What does an Odds Ratio (OR) value of 1.0 signify in a case-control study?

No association between the exposure and the disease

Which of the following is a disadvantage of a case-control study?

Establishing causality

In a case-control study, being unable to calculate cumulative incidence is primarily due to:

Unattainable time at risk for cases

Why are case-control studies not useful for rare exposures?

Lack of statistical power

What is a key advantage of using a control group in a case-control study?

Balancing confounding variables

If an Odds Ratio (OR) is significantly greater than 1.0, what interpretation can be made regarding the exposure and disease relationship?

There is a causal relationship

What is the primary purpose of random allocation in a Randomized Control Trial (RCT)?

To minimize bias and eliminate selection bias

Why is double-blinding considered the most preferred study design to establish causality in RCTs?

It provides great internal validity by keeping both subjects and investigators unaware of group allocation

What is the key advantage of maintaining frequent contact as a method to increase compliance in RCTs?

It can enhance compliance by regularly engaging with study participants

In what way does using a dispensing device contribute to increased compliance in RCTs?

It guarantees that all participants receive the same treatment dose

Why does noncompliance lead to inaccurate results in RCTs?

Because it increases differences between groups and affects data analysis

What is a significant disadvantage of randomization in RCTs?

It increases internal validity but decreases external validity

Which of the following is NOT a component of the evidence of causality in epidemiology?

Cessation of Exposure

If a study's findings cannot be replicated by independent investigators or in different populations, what aspect of evidence of causality is compromised?

Replication of the Findings

What does the term 'Specificity of the Association' imply in the context of determining causality?

The exposure should have a specific effect on only one disease

Why is biologic plausibility considered a crucial element in establishing causality in epidemiology?

It provides a biological mechanism to explain the relationship between exposure and disease

In epidemiology, what does the 'Dose-Response Relationship' indicate regarding exposure and disease?

A stronger exposure is always associated with a higher risk of disease

What distinguishes a Quasi-Experimental Study from an Experimental Study?

It does not require random allocation.

In a Posttest-Only with Control Group type of study, what differentiates group B from group A?

Group B is analyzed after the intervention happens.

What is a primary disadvantage of Natural Experiments compared to Randomized Control Trials (RCTs)?

Natural Experiments struggle to rule out alternative explanations.

What is the significance of a P-Value less than 0.05 in hypothesis testing?

The results are considered statistically significant

In hypothesis testing, what does it mean if a study has a P-Value greater than 0.05?

The null hypothesis (H0) is accepted

What are the disadvantages of using P-Value in hypothesis testing?

Does not imply medical significance

How can random error be reduced in a study?

Increasing sample size and repeating the study

What is the purpose of hypothesis testing in epidemiological studies?

Determining the significance of random error

Why is it important to understand that P-Value is probabilistic and not deterministic in hypothesis testing?

To interpret results correctly

What is a potential limitation related to the width of a Confidence Interval?

Determines public health significance

How can bias be avoided in research studies?


What type of bias is created during the assembly process of placing subjects into groups?

Selection Bias

When is bias likely to occur during the research process?

During the analysis stage

What is the primary purpose of a Confidence Interval in epidemiological studies?

To quantify random error

What does it mean if a Confidence Interval includes the null value?

The P-Value is Ӥ0.05

The Sensitivity of a screening test is calculated by:

Dividing the true positive cases by the total amount of cases of the disease

What is the primary reason why Sensitivity and Specificity are inversely proportional in screening tests?

To maintain a balance between detecting true positives and true negatives

Positive Predictive Value (PPV) in screening tests is defined as:

The probability that a positive test result will be the disease

What is Negative Predictive Value (NPV) in screening tests primarily based on?

The probability that a negative test result will not be the disease

What aspect of a disease does Detectable Pre-Clinical Phase (DPCP) aim to address?

Diagnosis before symptoms develop

In the context of screening tests, High Reliability refers to:

The possibility of reproducible test results

What is the primary purpose of Reflective Listening in patient interactions?

To reinforce the patient's strengths and commend goals

Which level of Reflective Listening involves the provider inferring the meaning and reflecting it back to the patient?


In Reflective Listening, what does 'Reflections of feeling' entail?

Inferring and reflecting the implied meaning with emotional emphasis

What is a common misconception about the Goals of Reflective Listening?

It focuses on repeating what the patient says word for word

How does Reflective Listening aim to diffuse resistance in patients?

By emphasizing positive statements about change made by the patient

What is a key element to consider in order for motivational interviewing to work effectively?

Patient's ability to admit having a problem

Which type of motivation is influenced by personal desires and those close to the patient?

Intrinsic motivation

What is one of the goals of eliciting permission, providing feedback in a non-threatening manner, and eliciting the person's interpretation in motivational interviewing?

To keep the conversation non-threatening

Which type of questions form the foundation of motivational interviews by encouraging open communication?

Open-ended questions

What should be avoided according to the principles of motivational interviewing?

all of the above

What characterizes a patient in the 'High Confidence' stage of change?

Having a strong belief in the decision

During the Clinical Discovery Phase of Community Water Fluoridation, why did Frederick McKay DDS find brown intrinsic teeth stains (mottled enamel)?

Only in long-term residents of Colorado Springs

What level of water fluoridation was determined as the balance between caries prevention and fluorosis during the Epidemiological Phase?

0.7-1.2 ppm

In what stage of change is a patient who is unsure of their decision to change or not change?

Low Confidence

What was the main source of the brown intrinsic teeth stains discovered by Frederick McKay DDS?

Drinking water from deep artesian wells

Which stage of change involves a patient who is stuck between wanting to change and not wanting to change?

'Ambivalent' stage

During the Clinical Discovery Phase, what type of residents did Frederick McKay DDS find to have brown intrinsic teeth stains due to mottled enamel?

Long term residents

In the Epidemiological Phase, what was the determined range of water fluoridation levels for the best balance between caries prevention and fluorosis?

0.7-1.2 ppm

What was the primary goal of the Demonstration Phase in conducting clinical trials in pairs of cities?

To determine the results of water fluoridation

What is considered one of the 10 great public health achievements of the 20th century according to the text?

Water fluoridation

Why was 0.7 ppm of fluoride determined as the balance for water fluoridation regardless of the ambient temperature zone?

Toothpaste and mouthwash containing more fluoride

What role did deep artesian wells play in causing mottled enamel according to Frederick McKay DDS?

They contained high levels of fluoride

What is the main difference between Topical [Post-Eruptive] Effects and Systemic [Pre-Eruptive] Effects of fluoride, as described in the text?

Topical effects involve remineralizing tooth enamel, while systemic effects focus on making enamel resistant to demineralization

What is the role of fluoride in tooth formation according to the Systemic [Pre-Eruptive] Effects concept?

Fluoride is built into the enamel to resist demineralization

What has been the general trend in tooth decay rates due to water fluoridation?

Water fluoridation has led to a 25% reduction in tooth decay

What is one potential danger highlighted in the text regarding fluoride toxicity?

Fluoride toxicity can be achieved by ingesting excessive fluoridated water within a short time frame

What is a major argument presented against community water fluoridation as discussed in the text?

It is considered forced mass medication of the public

What economic benefit does the text mention regarding savings from investing in fluoridation?

$1 invested in fluoridation saves $38 in avoided dental treatment costs

What is a major challenge faced by the Dental Care Delivery System's Safety Net System?

Underfunding and limited capacity

Which segment of the US population is mentioned to have the highest level of health disparities in terms of access to dental care?


What characterizes the Traditional Dental Workforce according to the information provided?

Includes dental hygienists and laboratory technicians

What is a significant advantage of the Private Practice Model in terms of payment methods?

Diverse payment options including private insurance and out-of-pocket payments

What is a critical need highlighted in the text that necessitates the existence of an Alternative Dental Workforce?

Addressing the shortage of dentists in certain areas

Why does the text emphasize the importance of the goal of health equity in relation to access to dental care?

To address disparities and promote the highest level of health for all

Which aspect of an association makes causality more likely according to the text?

The strength of the association

What did W. Hunter discover in 1911 regarding infections in the mouth?

Infections in the mouth can cause problems in other parts of the body

What is the primary benefit of nonsurgical periodontal therapy according to the text?

No improvement in patient outcomes

When considering causality, what should happen in relation to cause and effect?

Cause should happen before the effect

Which type of infection theory suggests that infections in the mouth can lead to problems in other parts of the body?

Focal Infection Theory

What is the association between periodontal disease and coronary heart disease based on studies?

There is a proven link between periodontal disease and coronary heart disease

Study Notes

Measures of Disease Frequency

  • Epidemiology: the study of factors affecting health and illness in human populations, focusing on frequency, distribution, and determinants of health-related states and events.
  • Types of populations:
    • Fixed population: permanent membership, defined by an event (e.g. baby boomers)
    • Dynamic population: transient membership, defined by being in or out of a state (e.g. students in a school)

Disease Frequency

  • Prevalence: proportion of people with a disease at a point in time, divided by the total population
    • Types:
      • Point prevalence: proportion of people with a disease at a specific moment in time
      • Period prevalence: proportion of people with a disease within a range of time
  • Incidence: ratio of new cases of a disease, divided by the population at risk
    • Types:
      • Cumulative incidence (CI): proportion of new cases within a range of time, divided by the population at risk at the beginning
      • Incidence rate (IR): proportion of new cases within a range of time, divided by the total time each member of the population is at risk
    • Person-time rate: involves accruing total time each member of the population is at risk

Measures of Association

  • 2x2 table: comparison of disease presence and exposure to a risk factor
  • Prevalence ratio: ratio of prevalence between exposed and unexposed groups
  • Rate ratio (RR): ratio of cumulative incidence between exposed and unexposed groups, showing the strength of the association
  • Rate difference (RD): difference in cumulative incidence between exposed and unexposed groups, measuring public health impact

Study Designs

  • Descriptive studies: generate hypotheses, communicate clinical observations, and serve as the first step for analytical studies
    • Case reports: detailed report of a single case, identifying new diseases or risk factors
    • Case series: detailed report of a group of cases with similar problems
    • Cross-sectional studies: observe exposure and disease at a single point in time
    • Ecological studies: observe aggregate data from an entire population

Analytical Studies

  • Observational studies: test hypotheses, comparing groups, and observing what occurs naturally
    • Cohort studies: groups are determined by a common characteristic, and the development of disease is examined over time
    • Case-control studies: determine the differences between those with and without a disease, analyzing their exposure history
  • Experimental studies: healthy subjects are randomly placed into two groups, one exposed and one not, and followed to determine disease development
    • Randomized control trials (RCTs): the most preferred study design to establish causality, with high internal validity
      • Steps: enroll participants, random allocation, blinding, follow-up, and determine the outcome
    • Quasi-experimental studies: similar to experimental studies, but occur naturally, without random allocation
      • Types: posttest-only, pretest-posttest, and interrupted time series

Concepts of Studies

  • Validity:
    • Internal validity: determined by study design and analysis, confirming whether study conclusions reflect the study sample
    • External validity: determined by the applicability of study results to the larger population
  • Bias: any systematic error in the study design, data collection, or analysis that can lead to incorrect conclusions### Research Study Design
  • Reproducibility: determines if recreating the study will yield the same results
  • Causality: determines the association between the exposure and the disease
    • Works well for infectious diseases
    • Evidence of causality includes:
      • Relationship in time: exposure should come before the disease
      • Strength of association: calculate RR, RD, and OR to determine the association
      • Dose-response relationship: the stronger the exposure, the higher the yield of cases of disease
      • Replication of the findings: similar results should be reproducible with a similar study
      • Biologic plausibility: must make sense from a biologic point of view
      • Consideration of alternative explanations
      • Cessation of exposure
      • Specificity of the association
      • Consistency with other knowledge

Error in Research

  • Type 1 error (False Positive): observing a difference between groups that is not there
  • Type 2 error (False Negative): missing a difference between groups that is there
  • Sources of error:
    • Random error: false results derived from the observation of things that happened by chance
    • Reducing random error: increasing sample size, repeating the study and measurements, and hypothesis testing
    • P-Value: determines the probability of the results and H0 being related
      • If P-Value ≤ 0.05, then the results are considered statistically significant
      • If P-Value > 0.05, then the results are considered statistically insignificant
    • Disadvantages of P-Value:
      • Does not rule out bias
      • Does not rule out confounding
      • Does not imply medical significance
      • Does not imply biological significance
      • Does not imply public health significance
    • Confidence Intervals: involves a curve on a graph whose width determines the random error
      • Wide CI indicates high random error
      • Narrow CI indicates low random error

Screening for Disease

  • Detectable pre-clinical phase (DPCP): includes the time span after the disease is detectable by a screening and before symptoms develop
  • Characteristics of a good screening test:
    • Simple
    • Acceptable
    • Cheap
    • No risk of morbidity
    • High reliability
    • High validity
    • Test validity: ideally, sensitivity and specificity would each be 1.0
    • Sensitivity: probability that a diseased person will test positive
    • Specificity: probability that a non-diseased person will test negative
    • Positive predictive value (PPV): probability that a positive test will be the disease
    • Negative predictive value (NPV): probability that a negative test will not be the disease

Motivational Interviewing

  • Goal: build motivation for change and sustain that change over time
  • Patient-centered approach
  • Types of motivation:
    • Intrinsic: derived from personal desires
    • Extrinsic: influenced by the environment
  • Goals for health behavior change:
    • Treatment entry
    • Treatment adherence
    • Treatment engagement
    • Treatment response
    • Maintenance of treatment
  • OARS: open-ended questions, affirmations, reflective listening, and self-motivational statements
  • Levels of reflective listening:
    • Repeating
    • Rephrasing
    • Paraphrasing
    • Reflections of feeling
    • Complex reflections of meaning

Community Water Fluoridation

  • History:
    • Clinical discovery phase (1901-1933)
    • Epidemiological phase (1933-1945)
    • Demonstration phase (1945-1954)
    • Technology transfer phase (1950-present)
  • Mechanisms of action:
    • Topical [post-eruptive] effects
    • Systemic [pre-eruptive] effects
  • Safety and benefits:
    • Reduced tooth decay by at least 25%
    • Especially benefits children, the poor, and those with limited access to dental care
    • Provides overall decrease in oral health problems
  • Regulations:
    • Environment Protection Agency (EPA)
    • The Safe Drinking Water Act
    • FDA
    • DHHS
  • Fluoride toxicity:
    • Can be achieved by ingesting large amounts of fluoridated water
    • Babies and children are more susceptible to fluoride toxicity
  • Arguments against fluoridation:
    • Not FDA approved
    • No RCTs have been conducted
    • Considered a forced mass medication of the public
    • Fluoride used is not pharmaceutical quality
  • Savings:
    • $1 invested in fluoridation saves $38 in avoided costs for dental treatment
    • Average of $1 per person per year is spent on fluoridation

Access to Dental Care

  • Disparities:
    • Poor populations
    • Racial-ethnic minorities
    • Special needs individuals
    • Uninsured
    • Public insurance
    • Individuals living far from a dental practice
    • Fear of the dentist
    • Oral health ignorance
    • Not enough dentists in an area
  • Dental care delivery system:
    • Private practice model
    • Safety net system
    • Alternative dental workforce
  • Oral systemic disease associations:
    • Life in general is less satisfying due to condition of mouth and teeth
    • Oral health affects the quality of life
    • Physically, socially, and psychologically
  • Criteria for causality:
    • Strength
    • Consistency
    • Specificity
    • Temporality
    • Biological gradient
    • Plausibility

Explore the basics of epidemiology with a focus on measures of disease frequency. Learn about the importance of studying factors affecting the health and illness of human populations, including frequency, distribution, and determinants of health-related states and events. Understand the concepts of fixed and dynamic populations, along with the differences among ratio, proportion, and rate.

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