Epidemiology Midterm (Weeks 1, 2, & 3)

Observational studies

Define the type of studies:

- One or more groups are observed.

- Characteristics about the observed are recorded described and analyzed.

Experimental/Intervention Studies

Define the type of studies:

- Investigator controlled intervention/exposure allocation such as treatment, procedure or drug therapy.

- Investigator analyzes effect of intervention/exposure on the study outcome.

1. Descriptive

2. Analytical

What are the 2 types of observational studies?

Descriptive studies

Define the type of studies:

Investigator observes the patterns of the exposure and the other variables in the study.

Descriptive

Are case studies/case reports considered descriptive or analytical observational study designs?

Descriptive

Are case series considered descriptive or analytical observational study designs?

Descriptive

Are cross-sectional studies (without comparison) considered descriptive or analytical observational study designs?

Analytical

Are case-control studies considered descriptive or analytical observational study designs?

Analytical

Are cohort studies considered descriptive or analytical observational study designs?

Analytical

Are cross-sectional (with comparison) considered descriptive or analytical observational study designs?

True

T/F: Cross-sectional studies can be descriptive as well as analytical

Descriptive studies

What type of study has the following characteristics?

- Helpful in observing trends or patterns for the main variables of interest as well as in relation to covariates.

- Helpful in generating research hypotheses for larger studies.

- Investigator observes and collects information on the variables of interest in the study.

- Investigator does not change any of the study aspects.

Descriptive studies

What type of study has the following characteristics?

- Typically used to describe and characterize who? (exposure group), where? (population source or location), and when? (time period) in relation to the what (outcome)

- Used to measure the relationship between exposure and outcome

- Direction of relationship cannot be determined

Experimental/interventional studies

What type of study has the following characteristics?

1. Controlled trials (parallel controls or self-controlled)

- Trials that include an experimental group and a control or comparison group

- Examples:

- - Randomized versus non-randomized

- - Design variations - Cross-over, split mouth

2. Trials with no controls or external controls

1. Human subjects

2. In-vitro experiments

3. Animal studies

What are 3 types of subjects in study designs?

1. Systemic reviews and meta-analyses

2. Randomized controlled trials

3. Cohort studies

4. Case-control studies

5. Cross-sectional studies

6. Case reports/series

7. Expert opinion

8. Anecdote

What is the hierarchy of evidence? (8) from most valid → least

Exposure

Define the following:

- Characteristic of the individual (age, gender, weight) or a variable related to environment (air pollution), lifestyle (smoking, exercise), social status (poverty or income level) or participant's background (education level, race/ethnicity).

- AKA a 'risk factor'.

Outcome

Define the following:

- Term representing the result or effect of interest in the study.

- Ex: Presence of disease, health status, success of treatment.

- Some studies may have multiple outcomes and multiple exposures.

Cases

Define the following:

- Main group of interest in a study

- In observational studies referred to as ___________

- In experimental studies referred to as treatment or intervention group

Controls

Define the following:

- Comparison group

- Sometimes referred to as non-cases.

- In experimental studies this is referred to as non-treatment or ____________ group.

Case study

What type of study has the following characteristics?

- Characteristics of a patient is recorded and published in a report (ex: case reports)

- No control is used

- Usually short duration of study

- Precursor to future studies (hypothesis generating)

B. Present

Which of the following time frames do case studies take part in?

A. Past

B. Present

C. Future

Case-series

What type of study has the following characteristics?

- Characteristics of a series of patients are recorded and published in a report (ex: case reports)

- Looking at same condition or treatment in a series of patients

- To observe trends or patterns

- No controls used (rarely comparison set of patients included)

- Short duration of study

- Precursor to larger studies (hypothesis generating)

1. Easy to conduct

2. Short duration

3. Inexpensive

4. Useful for generating hypotheses for larger studies

4 advantages of case report + series

1. We cannot evaluate associations

2. Generalizability is an issue

2 disadvantages of case report + series

B. Present

Which of the following time frames do case series take part in?

A. Past

B. Present

C. Future

Descriptive cross-sectional study

What type of study has the following characteristics?

- Useful in describing the characteristics of a population at one point in time (a slice of time to see what is happening).

- Useful in describing the characteristics such as knowledge, attitude and practices in the population.

Cross-sectional study

In this sample say you want to evaluate the prevalence of children wearing eye-glasses. Then you add up the number of kids wearing glasses and divide by the total. In this case it would be 4/6 = 60%. What type of study is this?

Cross-sectional study

What type of study does this image show?

Descriptive cross-sectional study

What type of study has the following characteristics?

- Sometimes referred to as prevalence studies as they can be used to examine prevalence of a disease or condition Ex: Surveys, Epidemiologic studies

- Can be short or long duration.

- Can be precursor to cohort and case-control studies.

True

T/F: You can use cross-sectional study design to study...

- Incidence patterns or mortality rates over a period of time.

- Make comparisons by race/ethnicity or time period.

- Estimate overall incidence rates and adjusted rates

1. Convenient

2. Less time consuming

3. Large samples

4. Can be done with limited resources

4 advantages of descriptive cross-sectional studies

1. Cannot evaluate causal associations as we cannot determine direction of association.

2. Participation bias in studies that use surveys and interviews.

3. Interview or reporting bias can also occur.

4. Investigation conducted at a slice of time --> this may not be representative of the full picture

4 disadvantages of descriptive cross-sectional studies

B. Present (fixed slice of time)

Which of the following time frames do descriptive cross-sectional studies take part in?

A. Past

B. Present

C. Future

Analytical

What type of study has the following characteristics?

- Analytical studies test the research hypothesis about the exposure-outcome relationship that is under investigation.

- We can measure the association between the exposure and outcome.

- We can evaluate the magnitude of the association between exposure and outcome.

- Ex: Does smoking status (never, past and current) have an effect on periodontal disease status (yes/no)

Analytical

Cross sectional, case control and cohort studies are all examples of what type of study?

Analytical cross-sectional study

What type of study has the following characteristics?

- Association between exposure and outcome at one point in time is evaluated.

- Magnitude of relationship estimated but not direction

Descriptive

Descriptive or analytical cross-sectional study?

- Overall disease burden can be described in large populations.

Descriptive

Descriptive or analytical cross-sectional study?

- Disease patterns can be described with this design.

Descriptive

Descriptive or analytical cross-sectional study?

- Can be utilized to generate research question or hypothesis for future studies.

Analytical

Descriptive or analytical cross-sectional study?

- In addition to describing disease burden, disease patterns and trends, relationship between exposure and outcome can be analyzed.

Analytical

Descriptive or analytical cross-sectional study?

- Research hypothesis/research question can be evaluated statistically

Analytical

Descriptive or analytical cross-sectional study?

- Odds ratios for the relationship between exposure and outcome can be estimated

1. Easy to conduct.

2. Commonly used to describe burden of disease, disease trends, behavioral patterns etc.

3. Correlation between variables can be determined and cross-sectional relationships can be analyzed.

3 advantages of analytical cross-sectional studies

1. Requires a large sample size.

2. Requires time, money and resources.

3. Cannot establish causal association.

4. Cannot establish time sequence or temporality.

4 disadvantages of analytical cross-sectional studies

Case-control study

What type of study has the following characteristics?

- Compares diseased individuals to non-diseased individuals - in relation to exposure status

- Cases - have the outcome of interest

- Controls or non-cases - do not have the outcome

- Retrospective in nature

- Start in present time and go back in time to evaluate risk factor exposure

- Analyze factors/exposures related to outcome in cases and controls

- We measure the odds of disease among exposed versus odds of exposure among those with disease versus those without disease

Case-control study

What type of study has the following characteristics?

- At the start of the study, the disease or outcome has already occurred, and cases and controls are grouped based on the outcome/disease status.

- Exposure variables of interest are identified among cases and controls.

- Information on contributing factors and exposure(s) is obtained retrospectively (review of medical/dental charts, interviews or surveys).

Cases

In a case control study, will the cases or the controls have the outcome of interest?

- Controls can be selected from the same community, location or hospital.

- Similar characteristics as cases except for disease status

- Evaluate exposure information in controls in the same manner as cases

What is some of the criteria for selecting controls in a case-control study?

Case-control study

What type of study does this image show?

Case-control study

In this sample say you want evaluate the variables that may have contributed to children wearing eye-glasses. So we can compare the children with eye-glasses to children not wearing eye-glasses. We can retrospectively collect information like family history, medical history, tv-watching, etc. We can then evaluate the odds of these possible risk factors to the outcome of children wearing eye-glasses (outcome could be astigmatism, myopia). What type of study is this describing?

Present and past (retrospective)

Which of the following time frames do case-control studies take part in?

A. Past

B. Present

C. Future

Odds ratios

Association between exposure-outcome can be evaluated by estimating ____________

Odds ratios

____________ are estimated based on the probability of disease among exposed individuals relative to the probability of disease among unexposed individuals.

1. Efficient in design

2. Shorter duration

3. Less expensive

4. Convenient for studying many exposures

5. Efficient for rare diseases and for diseases with long latency period

6. Measures of association can be calculated to evaluate exposure-outcome relationship (Odds ratio)

6 advantages of case-control studies

1. Retrospective nature of the study

2. Difficult to establish time sequence of the exposure-outcome relationship

3. Retrospective nature of the design leads to potential biases

3 disadvantages of case-control studies

Recall bias

Define the following:

Cases recall information differently when compared to controls

Recall bias (Cases remember and report their previous exposure experience differently from controls)

What is the most common type of bias in case-control studies?

Recall bias

What type of bias is this?

Moms of children with orofacial clefts recall risks more accurately

True

T/F: Recall bias can occur in cross-sectional studies

Interviewer bias

Define the following:

Differences that occur in the recording or interpretation of information from participants

Interviewer bias

In cross-sectional, case-control and cohort studies, knowledge of a subject's disease status or exposure status may lead to increased questioning by the interviewer. This is known as _____________

Interviewer bias

What type of bias is this?

Those with periodontal disease are examined more frequently to evaluate oral health status versus those without

Interviewer bias

What type of bias is this?

Those who smoke are interviewed more to evaluate oral health status versus those who do not smoke

Reporting bias

What type of bias is this?

- Cross-sectional, Case-control and cohort studies: Under-reporting of socially undesirable behaviors (Smoking, drinking)

- Over-reporting (Exposure to chemicals, fluoride in water)

- Cases may refuse to answer sensitive questions (Substance abuse)

Case-control studies

Misclassification bias is most common in what type of studies?

Misclassification bias

What type of bias is this?

- Inaccurate case definitions or inclusion/exclusion criteria

- Participants are incorrectly 'assigned' or categorized into the wrong exposure or outcome group

- Can lead to diluted or exaggerated effects

Cross-sectional

Cross-sectional or case-control study?

Assessed at a point in time (slice of time)

Cross-sectional

Cross-sectional or case-control study?

Trends and relationships between exposure and outcome variables described and analyzed.

Cross-sectional

Cross-sectional or case-control study?

Temporality cannot be established.

Case-control

Cross-sectional or case-control study?

Assessed retrospectively.

Case-control

Cross-sectional or case-control study?

Association between exposure and outcome can be estimated.

Case-control

Cross-sectional or case-control study?

If information is available about exact time period of exposure and date of diagnosis it is possible to establish temporality.

Cohort study

What type of study has the following characteristics?

- Prospective or longitudinal studies.

1. Start with a group of people and identify an exposure.

2. Divide the cohort into exposed and unexposed groups (Smokers versus non-smokers).

3. Follow them over a period of time to observe the outcome (periodontal disease).

4. At the end of the study determine incidence of outcome among exposed versus unexposed.

Cohort

Define the following:

Any designated group of individuals

Cohort study

What type of study does this image show?

Cohort study

What type of study has the following characteristics?

- Compare disease rates among exposed vs. unexposed

- Record newly developed cases during follow-up

- Can calculate incidence (proportions) + incidence rates

- Due to prospective nature time sequence of events can be established

Present and future

Which of the following time frames do cohort studies take part in?

A. Past

B. Present

C. Future

1. In terms of efficiency most similar to randomized clinical trials

2. Can be more ethical in certain cases than clinical trials

3. Good for rare exposures

4. Agriculture pesticide and cancer

5. Can look at multiple outcomes due to single exposure

6. Can estimate incidence rates over time as we have time information

7. Can be used to establish temporality and causality

7 advantages of cohort studies

1. Not efficient for rare diseases

2. Long duration can cost time and money

3. Need additional resources

4. Exposure status may change over time (smoking or drinking patterns)

5. Prone to loss to follow-up bias

5 disadvantages of cohort studies

Case control

Case control or cohort study?

Participants are grouped by disease status

Case control

Case control or cohort study?

Utilizes less time and money

Case control

Case control or cohort study?

Can be used for rare diseases

Case control

Case control or cohort study?

Multiple exposures can be studied

Case control

Case control or cohort study?

Does not work well for rare exposures

Case control

Case control or cohort study?

Prone to recall bias/information bias

Cohort study

Case control or cohort study?

Participants are grouped by exposure status

Cohort study

Case control or cohort study?

Long duration of follow-up so utilizes more time and resources

Cohort study

Case control or cohort study?

Can be used for rare exposures

Cohort study

Case control or cohort study?

Multiple outcomes can be evaluated

Cohort study

Case control or cohort study?

May not work well for rare diseases

Cohort study

Case control or cohort study?

Prone to loss to follow-up bias due to dropouts

Systemic reviews and meta analysis

What is at the top of the hierarchy of evidence?

Anecdote

What is at the bottom of the hierarchy of evidence?

Systematic reviews

Define the following:

Seek to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question. They aim to minimize bias by using explicit, systematic methods documented in advance with a protocol.

Systematic reviews

What type of study has the following characteristics?

- A detailed review of published articles on a particular research question

- Search criteria, inclusion and exclusion criteria, and time period are defined clearly

- Multiple study design types can be included

- All types of analytical observational studies

- Summarize the evidence from the included studies

1. Efficient way to summarize information from different sources

2. Results can be more broadly generalized

3. Most reliable than individual studies as we are summarizing information from multiple studies

4. Quality of information highest (recall hierarchy of evidence pyramid)

4 advantages of systematic reviews

1. Laborious

2. Time consuming

3. May be difficult to combine information when methods and measures vary across studies

3 disadvantages of systematic reviews

Meta-analysis

Define the following:

Quantitative, formal epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research

Meta-analysis

What type of study has the following characteristics?

- Data from different studies are extracted, pooled and analyzed

- - Specific analytical methods are utilized

- - Specific software available to conduct the analysis

- The summarized data is used to make interpretations or causal inferences