Day 1 Study Designs Cross-Sectional Design 1

Health and disease are not distributed haphazardly in a population. Big Epi Idea

Health and disease are not distributed haphazardly in a population. There are patterns to their occurrence. Big Epi Idea

Health and disease are not distributed haphazardly in a population. There are patterns to their occurrence. These patterns can be identified through the surveillance of populations. Big Epi Idea

Health and disease are not distributed haphazardly in a population. There are patterns to their occurrence. These patterns can be identified through the surveillance of populations. Examining these patterns of health and disease can help formulate hypotheses about their possible causes. Big Epi Idea

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7 A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life. Anecdote Study Designs

8 Anecdote Science Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

9 Anecdote Science DZ Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

10 Anecdote Science Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

11 Anecdote Science Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

12 Transforming Anecdote to Science Study Designs

13 Absolutely nothing in the available arsenal of anti-emetics worked at all. I was miserable and came to dread the frequent treatments with an almost perverse intensity. I had heard that marijuana often worked well against nausea. I was reluctant to try it because I had never smoked any substance habitually (and didn’t even know how to inhale). Moreover, I had tried marijuana twice (in the 1960s) … and had hated it …. Marijuana worked like a charm …. The sheer bliss of not experiencing nausea - and not having to fear it for all the days intervening between treatments - was the greatest boost I received in all my year of treatment, and surely the most important effect upon my eventual cure. Transforming Anecdote to Science Study Designs

14 Anecdote Science Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

Exposure (E) Outcome (O) Time 4 Basic Epidemiological Study Designs

17 4 Basic Epidemiological Study Designs

Exposure (E) Outcome (O) Sample Time Randomly Assigned E E O O O O Randomized Controlled Trial

Exposure (E) Outcome (O) Sample Time Randomly Assigned E E O O O O Cohort Study Cohort

Exposure (E) Outcome (O) Time O O E E E E Case-Control Study

Exposure (E) Outcome (O) Time E E O O Cross-Sectional Study

23 Anecdote Science Transforming Anecdote to Science Study Designs A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

25 4 Basic Epidemiological Study Designs LANY

26 An epidemiologic study in which subjects are assigned to groups to receive or not receive a hypothesized beneficial intervention. Randomized Controlled Trial

27 4 Basic Epidemiological Study Designs LANY Coffee Consumption and Sleep Duration

Just as in the controlled trial, the epidemiologist is also on the train during the entire journey. But there is an important difference. The epidemiologist is not telling passengers what to do. Rather, the epidemiologist is just observing them and counting. Passengers are not being told to have or not have an exposure, they are just living their normal lives. The epidemiologist, on the ride for the whole journey, just keeps observing everyone’s exposures and whether or not they develop the outcome during the journey. 4 Basic Epidemiological Study Designs

29 4 Basic Epidemiological Study Designs LANY Coffee Consumption and Sleep Duration

The epidemiologist is not on the journey. Rather, the epidemiologist is waiting at the train station at the end of the journey. As passengers get off the train, the epidemiologist selects a group of passengers with the outcome and a similar group of passengers without the outcome. The epidemiologist then asks each person in each group questions about their exposures during the train ride. The epidemiologist relies on passengers’ memories of their exposures that occurred during the trip. 4 Basic Epidemiological Study Designs

31 4 Basic Epidemiological Study Designs LANY Coffee Consumption and Sleep Duration

The epidemiologist, who has not been on the journey, stops the train somewhere during the trip (kind of like a train robbery) and takes a “snapshot” of all the passengers by asking them whether or not they have the exposure and whether or not they have the outcome. Then the epidemiologist leaves the train and goes home to analyze the data from that particular day. The journey continues without the epidemiologist. 4 Basic Epidemiological Study Designs

33 4 Basic Epidemiological Study Designs LANY Coffee Consumption and Sleep Duration

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35 4 Basic Epidemiological Study Designs Coffee Consumption and Sleep Duration Photography

36 4 Basic Epidemiological Study Designs RECORD Coffee Consumption and Sleep Duration Photography

37 4 Basic Epidemiological Study Designs Coffee Consumption and Sleep Duration Photography

38 4 Basic Epidemiological Study Designs Coffee Consumption and Sleep Duration Photography

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40 Strengths Randomized Controlled Trial Randomization distributes possible confounders equally in exposed and unexposed Easier to blind / mask than observational studies

41 Randomized Controlled Trial Expensive in terms of time and money Volunteer biases: participates may not be representative of the population Loss to follow-up attributed to treatment / exposure Limitations

42 Cohort Study Subjects in cohorts can be matched, which limits the influence of confounding variables Easier and cheaper than a randomized controlled trial Can establish time order of exposure and outcome Strengths

43 Cohort Study No randomization, which means that imbalances in participant characteristics could exist Outcome of interest could take time to occur Loss to follow-up Limitations

44 Case-Control Study Good for studying rare outcomes Less time needed to conduct the study because the outcome has already occurred Lets you simultaneously look at multiple exposures Useful as initial studies to establish an association Strengths

45 Case-Control Study Problems with data quality because of reliance on memory People with a condition will be more motivated to recall exposures (also called recall bias) It can be difficult to find a suitable control group Inability to determine with certainty the time order of the exposure and the outcome Limitations

46 Cross-Sectional Study Relatively quick and easy to conduct (no long periods of follow-up) Data on all variables are only collected once Able to measure prevalence for all factors under investigation Multiple outcomes and exposures can be studied Strengths

47 Cross-Sectional Study Difficult to determine whether the outcome followed exposure in time or exposure resulted from the outcome. Not suitable for studying rare outcomes or outcomes with a short duration. As cross-sectional studies measure prevalent rather than incident cases, the data will always reflect determinants of survival as well as etiology. Susceptible to bias due to low response and misclassification due to recall bias. Limitations

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49 Randomized Controlled Trial Typical Measure of Effect (A way of quantifying the extent to which an exposure and an outcome are associated) Relative Risk or Risk Ratio

50 Cohort Study Typical Measure of Effect (A way of quantifying the extent to which an exposure and an outcome are associated) Relative Risk or Risk Ratio

51 Case-Control Study Typical Measure of Effect (A way of quantifying the extent to which an exposure and an outcome are associated) Odds Ratio or Relative Odds

52 Cross-Sectional Study Typical Measure of Effect (A way of quantifying the extent to which an exposure and an outcome are associated) Prevalence Ratio

54 4 Basic Epidemiological Study Designs

55 4 Basic Epidemiological Study Designs The goal of every epidemiological study is to harvest valid and precise information about the relationship between an exposure and a disease in a population. The various study designs merely represent different ways of harvesting this information. Essentials in Epidemiology in Public Health Ann Aschengrau and George R. Seage III

56 4 Basic Epidemiological Study Designs The goal of every epidemiological study is to harvest valid and precise information about the relationship between an exposure and an outcome in a population. The various study designs merely represent different ways of harvesting this information. Essentials in Epidemiology in Public Health Ann Aschengrau and George R. Seage III

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. When an exposure is hypothesized to have a detrimental effect, it is not ethical to intentionally expose a group of people. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. When an exposure is hypothesized to have a detrimental effect, it is not ethical to intentionally expose a group of people. In these circumstances, studies can be designed that observe groups of free-living people with and without the exposure. Big Epi Idea

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Epi Team Challenge X-Sectional Study Randomized Controlled Trial Case-Control Study Cohort Study What’s My Design?

Epidemiologist is involved during the entire time from exposure to outcome. Assign participants to treatment and control groups. Follow through time and compare risk of the outcome in treatment group with risk of the outcome in control group. Give exposure to treatment group, but not control group. RCT What’s My Design? Guided Practice

Epidemiologist is involved during the entire time from exposure to outcome. Select a healthy study sample. Follow through time and compare risk of the outcome in exposed group to risk of the outcome in unexposed group. Observe who has and has not been exposed. Cohort Study What’s My Design? Guided Practice

Epidemiologist is involved after the outcome has occurred and relies on subjects’ memories to gather information about exposure. Select a group of people with the outcome and a similar group of people without the outcome. Compare the odds of exposed people in the two groups. Ask both groups about their exposures in the past. Case-Control Study What’s My Design? Guided Practice

Ask each person about both exposure and outcome at one point in time. Prevalence of outcome in exposed group is compared to prevalence of outcome in unexposed group. Select a study sample. Cross-Sectional Study What’s My Design? Guided Practice

Sample E E O O O O Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

The epidemiologist, who has not been on the journey, stops the train somewhere during the trip (kind of like a train robbery) and takes a “snapshot” of all the passengers by asking them whether or not they have the exposure and whether or not they have the outcome. Then the epidemiologist leaves the train and goes home to analyze the data from that particular day. The journey continues without the epidemiologist. Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

O O E E E E Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

Sample Randomly Assigned E E O O O O RCT What’s My Design?

4 Basic Epidemiological Study Designs

RECORD Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

E E O O Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

Randomly Assigned RCT What’s My Design?

4 Basic Epidemiological Study Designs

Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

Sample Randomly Assigned E E RCT What’s My Design?

4 Basic Epidemiological Study Designs

RCT What’s My Design?

4 Basic Epidemiological Study Designs

Just as in the controlled trial, the epidemiologist is also on the train during the entire journey. But there is an important difference. The epidemiologist is not telling passengers what to do. Rather, the epidemiologist is just observing them and counting. Passengers are not being told to have or not have an exposure, they are just living their normal lives. The epidemiologist, on the ride for the whole journey, just keeps observing everyone’s exposures and whether or not they develop the outcome during the journey. Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

E E O O Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

E E E E Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

The epidemiologist is not on the journey. Rather, the epidemiologist is waiting at the train station at the end of the journey. As passengers get off the train, the epidemiologist selects a group of passengers with the outcome and a similar group of passengers without the outcome. The epidemiologist then asks each person in each group questions about their exposures during the train ride. The epidemiologist relies on passengers’ memories of their exposures that occurred during the trip. Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

Sample Randomly Assigned RCT What’s My Design?

4 Basic Epidemiological Study Designs

Sample E E O O O O Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

E E E E Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

O O O O RCT and Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

Sample RCT and Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

O O O O RCT and Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

What’s My Design? RCT and Cohort Study

4 Basic Epidemiological Study Designs

E E O O Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

O O E E E E Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

Sample Randomly Assigned E E O O O O RCT What’s My Design?

4 Basic Epidemiological Study Designs

Epidemiologist is involved during the entire time from exposure to outcome. Select a healthy study sample. Follow through time and compare risk of the outcome in exposed group to risk of the outcome in unexposed group. Observe who has and has not been exposed. Cohort Study What’s My Design?

4 Basic Epidemiological Study Designs

Epidemiologist is involved after the outcome has occurred and relies on subjects’ memories to gather information about exposure. Select a group of people with the outcome and a similar group of people without the outcome. Compare the odds of exposed people in the two groups. Ask both groups about their exposures in the past. Case-Control Study What’s My Design?

4 Basic Epidemiological Study Designs

Epidemiologist is involved during the entire time from exposure to outcome. Assign participants to treatment and control groups. Follow through time and compare risk of the outcome in treatment group with risk of the outcome in control group. Give exposure to treatment group, but not control group. RCT What’s My Design?

4 Basic Epidemiological Study Designs

Ask each person about both exposure and outcome at one point in time. Prevalence of outcome in exposed group is compared to prevalence of outcome in unexposed group. Select a study sample. Cross-Sectional Study What’s My Design?

4 Basic Epidemiological Study Designs

The goal of every epidemiological study is to harvest valid and precise information about the relationship between an exposure and an outcome in a population. The various study designs merely represent different ways of harvesting this information. Essentials in Epidemiology in Public Health Ann Aschengrau and George R. Seage III

Epi Team Challenge X-Sectional Study Randomized Controlled Trial Case-Control Study Cohort Study Which Design Is Best?

Study DesignsStrengthsLimitations RCT Cohort Study Case-Control Study Cross-Sectional Study Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Cohort Study Case-Control Study Cross-Sectional Study Which study design is the fastest? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Cohort Study Case-Control Study Cross-Sectional Study Fastest Which study design is the fastest? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Cohort Study Case-Control Study Cross-Sectional Study Fastest Which study designs are the most time consuming? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTTime Consuming Cohort Study Time Consuming Case-Control Study Cross-Sectional Study Fastest Which study designs are the most time consuming? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTTime Consuming Cohort Study Time Consuming Case-Control Study Cross-Sectional Study Fastest Which study design is the most scientifically sound? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Cross-Sectional Study Fastest Which study design is the most scientifically sound? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Cross-Sectional Study Fastest Which study design is best for studying rare outcomes? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Cross-Sectional Study Fastest Which study design is best for studying rare outcomes? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Cross-Sectional Study Fastest Which study designs do not identify the time order of the exposure and the outcome? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Which Study Design Is Best? Which study designs do not identify the time order of the exposure and the outcome?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion With which study design are you least certain of your results? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results With which study design are you least certain of your results? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCTMost Scientifically SoundTime Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results Which study design provides the best measure of exposure? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results Which study design provides the best measure of exposure? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results Which study design is the most accurate observational study? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Most Accurate Observational Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results Which study design is the most accurate observational study? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Most Accurate Observational Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Possible Time-Order Confusion Least Certain of Results Which study design is the least expensive? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Most Accurate Observational Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study design is the least expensive? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Cohort Study Most Accurate Observational Study Time Consuming Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study designs are the most expensive? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study designs are the most expensive? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study design would be unethical for harmful exposures? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Unethical for Harmful Exposures Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study design would be unethical for harmful exposures? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Unethical for Harmful Exposures Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Which study designs create the possibility of error in recalling past exposures? Which Study Design Is Best?

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Unethical for Harmful Exposures Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Possible Error in Recalling Exposures Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Possible Error in Recalling Exposures Which study designs create the possibility of error in recalling past exposures? Which Study Design Is Best?

Which study design is best? It depends ….

Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Most Expensive Unethical for Harmful Exposures Cohort Study Most Accurate Observational Study Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Possible Error in Recalling Exposures Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Least Certain of Results Possible Error in Recalling Exposures Which study design is best? Which Study Design Is Best? It depends ….

Which Study Design Is Best? It depends …. Whether the exposure is believed to be beneficial Time urgency How much is known about the association Money Regulations

Which Design Is Best? Study DesignsStrengthsLimitations RCT Most Scientifically Sound Best Measure of Exposure Time Consuming Unethical for Harmful Exposures Most Expensive Cohort Study Most Accurate Observational Study Good Measure of Exposure Time Consuming Most Expensive Case-Control Study Can Study Rare Outcomes Possible Time-Order Confusion Possible Error in Recalling Exposures Cross-Sectional Study Fastest Least Expensive Possible Time-Order Confusion Possible Error in Recalling Exposures It depends ….

174 4 Basic Epidemiological Study Designs The goal of every epidemiological study is to harvest valid and precise information about the relationship between an exposure and an outcome in a population. The various study designs merely represent different ways of harvesting this information. Essentials in Epidemiology in Public Health Ann Aschengrau and George R. Seage III

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Cross-Sectional Design 176

177 4 Basic Epidemiological Study Designs

178 A study in which exposure and outcome are measured simultaneously in a given population or a sample of that population. This study can be thought of as providing a "snapshot" of the frequency of an exposure and outcome at a particular point in time. Data that are collected as part of a cross-sectional study can be used to assess the prevalence of an outcome. Also called a prevalence study. Cross-Sectional Study

179 An observational study in which the presence or absence of an outcome and the presence or absence of a hypothesized cause of that outcome are identified in a population at one particular time. Cross-Sectional Study

Cross-sectional studies are carried out at one time point or over a short period. Cross-Sectional Study

Cross-sectional studies are carried out at one time point or over a short period. They are usually conducted to estimate the prevalence of the outcome of interest for a given population, commonly for the purposes of public health planning. Cross-Sectional Study

Cross-sectional studies are carried out at one time point or over a short period. They are usually conducted to estimate the prevalence of the outcome of interest for a given population, commonly for the purposes of public health planning. Data can also be collected on individual characteristics, including exposure to risk factors, alongside information about the outcome. Cross-Sectional Study

Cross-sectional studies are carried out at one time point or over a short period. They are usually conducted to estimate the prevalence of the outcome of interest for a given population, commonly for the purposes of public health planning. Data can also be collected on individual characteristics, including exposure to risk factors, alongside information about the outcome. In this way cross-sectional studies provide a 'snapshot' of the outcome and the characteristics associated with it, at a specific point in time. Cross-Sectional Study

185 Cross-Sectional Study Difficult to determine whether the outcome followed exposure in time or exposure resulted from the outcome. Not suitable for studying rare outcomes or outcomes with a short duration. As cross-sectional studies measure prevalent rather than incident cases, the data will always reflect determinants of survival as well as etiology. Susceptible to bias due to low response and misclassification due to recall bias. Limitations

186 Cross-Sectional Study Relatively quick and easy to conduct (no long periods of follow-up) Data on all variables are only collected once Able to measure prevalence for all factors under investigation Multiple outcomes and exposures can be studied Strengths

187 Cross-Sectional Study Typical Measure of Effect (A way of quantifying the extent to which an exposure and an outcome are associated) Prevalence Ratio

189 4 Basic Epidemiological Study Designs

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. When an exposure is hypothesized to have a detrimental effect, it is not ethical to intentionally expose a group of people. Big Epi Idea

A hypothesis can be tested by comparing the frequency of disease in selected groups of people with and without an exposure to determine if the exposure and the disease are associated. When an exposure is hypothesized to have a beneficial effect, studies can be designed in which a group of people is intentionally exposed to the hypothesized cause and compared to a group that is not exposed. When an exposure is hypothesized to have a detrimental effect, it is not ethical to intentionally expose a group of people. In these circumstances, studies can be designed that observe groups of free-living people with and without the exposure. Big Epi Idea

EPI CHALLENGE Proposal Form Cross-Sectional Study Design 4a. Describe how your hypothesis can be tested in your high school using the cross-sectional design. Include a diagram of the study design. 4b. Describe the advantages of using a cross-sectional study. 4c. Describe two or more challenges your team will face while testing this hypothesis in your school.

4 Basic Epidemiological Study Designs Handout