Medidas de Associação - Resumo - Epidemiologia

Summary

This video provides an in-depth explanation of epidemiological measures of association, focusing on prevalence, incidence, and risk measures in cohort and case-control studies. It clarifies key concepts such as how prevalence measures the total number of cases at a specific point in time, while incidence tracks new cases over a period. The video covers essential statistical tools like relative risk, attributable risk, and odds ratio, emphasizing their importance in understanding disease associations and drawing conclusions in epidemiological research. The presenter highlights the significance of interpreting these measures rather than just calculating them, with a focus on study validity and confidence intervals.

Takeaways

• 😀 Measures of occurrence in epidemiology, such as prevalence and incidence, help quantify the number of cases of a disease at a specific point in time or over a period.
• 😀 Prevalence refers to the total number of cases at a given time, while incidence focuses on new cases occurring within a specific time period.
• 😀 Prevalence and incidence are different metrics, and a disease can have a high prevalence but a low incidence.
• 😀 The relative risk in cohort studies compares the incidence of disease between exposed and non-exposed groups, helping identify associations between exposure and disease development.
• 😀 A relative risk of 1 means no association, greater than 1 suggests an increased risk with exposure, and less than 1 indicates a protective factor.
• 😀 Confidence intervals around relative risk values help assess the reliability of the findings. If the confidence interval includes 1, the result may not be significant.
• 😀 The attributable risk (absolute risk) measures the additional risk of disease due to exposure, calculated as the difference between the incidence in exposed and non-exposed groups.
• 😀 Attributable risk percentage expresses the proportion of disease cases in the exposed population that can be attributed to the exposure.
• 😀 The population attributable risk measures the additional risk in the total population due to exposure, considering both exposed and non-exposed groups.
• 😀 In case-control studies, the odds ratio (OR) is used instead of relative risk to assess the association between exposure and disease, since the study design focuses on outcomes (disease present or absent).
• 😀 The odds ratio is calculated as the ratio of the cross-products from a 2x2 table, and its interpretation mirrors relative risk with values greater than 1 indicating an increased risk, equal to 1 indicating no association, and less than 1 suggesting a protective effect.

Q & A

What is the main focus of this video script?

The video script focuses on explaining different epidemiological measures of association, including measures of occurrence (prevalence and incidence), and how they are applied in cohort and case-control studies.

What is the key difference between prevalence and incidence in epidemiological studies?

Prevalence refers to the total number of existing cases of a disease in a population at a specific point in time, while incidence refers to the number of new cases that develop during a defined period of time.

Why are prevalence and incidence considered different despite both measuring disease occurrence?

Prevalence includes both new and existing cases at a given time, whereas incidence only counts new cases that arise during a specific time period. Additionally, prevalence is influenced by factors such as migration, cure rates, and mortality.

What is the definition of relative risk in cohort studies?

Relative risk (or risk ratio) is the ratio of the incidence of a disease in the exposed group to the incidence in the non-exposed group. It is used to compare the likelihood of developing a disease based on exposure to a certain factor.

How do you interpret a relative risk of 1, greater than 1, and less than 1?

A relative risk of 1 indicates no association between exposure and disease. A relative risk greater than 1 suggests that exposure increases the risk of the disease, while a relative risk less than 1 indicates that exposure may reduce the risk, implying a protective effect.

Why is confidence interval important when calculating relative risk?

The confidence interval provides a range of values within which the true relative risk is likely to fall. A 95% confidence interval suggests that we are 95% confident the true value lies within this range. If the interval includes 1, the association may not be statistically significant.

What does 'risk attributable' (or attributable risk) measure in cohort studies?

Attributable risk measures the difference in disease incidence between the exposed and non-exposed groups. It helps quantify the additional risk of disease associated with exposure to a specific factor.

What is the meaning of the 'population attributable risk'?

Population attributable risk measures the additional risk of disease in the total population due to exposure, not just among the exposed group. It reflects the burden of disease that can be attributed to a specific exposure across the entire population.

Why can't relative risk be used in case-control studies?

In case-control studies, participants are selected based on whether they have or do not have the disease, rather than their exposure status. As a result, calculating relative risk isn't appropriate because the incidence of disease in the population is unknown.

What is the Odds Ratio (OR) and how is it used in case-control studies?

The Odds Ratio (OR) is used in case-control studies to compare the odds of exposure in individuals with the disease (cases) to those without the disease (controls). It is analogous to relative risk, but it is calculated using a 2x2 table and based on the odds of exposure.