Relative risk and risk ratios

Global Health with Greg Martin
7 Dec 202107:59
EducationalLearning
32 Likes 10 Comments

TLDRThe video script delves into understanding risk through a hypothetical cohort study, illustrating how risk is calculated and compared between different groups, specifically smokers and non-smokers. It explains concepts such as risk ratio, relative risk, and attributable risk using clear examples. The script also highlights the increased risk of certain health outcomes, like low birth weight babies, associated with smoking during pregnancy, emphasizing the importance of these concepts in public health research.

Takeaways
  • ๐Ÿ“Š To understand risk, follow a group over time and assess the incidence of a specific disease.
  • ๐Ÿงพ Calculate risk by dividing the number of people who got sick by the total number in the cohort.
  • ๐Ÿšฌ Smoking status can be used to compare risks between different groups, such as smokers and non-smokers.
  • ๐Ÿ”ข The risk ratio is calculated by dividing the risk in the exposed group (e.g., smokers) by the risk in the unexposed group (e.g., non-smokers).
  • ๐Ÿ“ˆ A risk ratio greater than one indicates increased risk due to exposure, while less than one suggests protection.
  • โž– The risk difference or attributable risk is found by subtracting the risk of the unexposed group from the exposed group.
  • ๐Ÿ‘ถ Real-world example: Smoking during pregnancy nearly doubles the risk of having a low birth weight baby.
  • ๐Ÿคฐ In a study of a thousand pregnant women, 12% of smokers had low birth weight babies compared to 6% of non-smokers.
  • ๐Ÿ“š Cohort studies begin with an exposure of interest, follow the cohort over time, and measure outcomes to compare with unexposed groups.
  • ๐Ÿ“ˆ The risk of an outcome can be represented using two by two tables for easy calculation of risks and ratios.
  • ๐Ÿ‘ฉโ€โš•๏ธ Healthcare professionals can enhance their skills through courses and programs offered by institutions like the Royal College of Physicians of Ireland.
Q & A

  • How is the risk calculated in the context of the given study?

    -The risk is calculated by dividing the number of individuals who developed the disease by the total number of individuals in the group. For example, if 17 out of 50 people got sick, the risk is 17/50, which equals 0.34 or 34%.

  • What does the risk ratio represent in a cohort study?

    -The risk ratio represents the comparison of the risk of a particular outcome (like a disease) between an exposed group (e.g., smokers) and an unexposed group (e.g., non-smokers). A risk ratio greater than one indicates that the exposure increases the risk, while a ratio less than one suggests a protective effect.

  • What is the relative risk of the 'disease of turning red' among smokers compared to non-smokers in the example?

    -The relative risk among smokers compared to non-smokers is 2.4, meaning smokers are 2.4 times more likely to get the 'disease of turning red' than non-smokers.

  • How is the risk difference or attributable risk calculated?

    -The risk difference or attributable risk is calculated by subtracting the risk in the unexposed group from the risk in the exposed group. It represents the additional risk associated with the exposure, such as smoking in the given example.

  • What does an excess risk of 0.28 signify?

    -An excess risk of 0.28 means that the risk associated with the exposure (smoking) is 0.28 higher than the background risk in the unexposed group (non-smokers).

  • What is the risk of having a low birth weight baby among non-smokers in the real-world example provided?

    -The risk of having a low birth weight baby among non-smokers is 0.063 or about 6 percent.

  • What is the relative risk of having a low birth weight baby if a mother smokes during pregnancy?

    -The relative risk is 1.9, indicating that smoking during pregnancy nearly doubles the risk of having a low birth weight baby.

  • What is the absolute risk increase for having a low birth weight baby if a mother smokes during pregnancy?

    -The absolute risk increase is 5.7 percent, which is the attributable risk or the excess risk of having a low birth weight baby due to smoking during pregnancy.

  • How does the two by two table help in understanding risk ratios and risk differences?

    -The two by two table organizes the numbers of individuals who experienced the outcome and those who did not within each group. It simplifies the calculation of risk ratios and risk differences by clearly displaying the relevant numbers for each group.

  • What is the significance of understanding risk ratios and risk differences in public health?

    -Understanding risk ratios and risk differences is crucial in public health as it helps identify and quantify the impact of various exposures on health outcomes. This information is vital for making informed decisions about interventions and policies aimed at improving population health.

  • How does the concept of a cohort study apply to the examples discussed in the script?

    -A cohort study follows a group of individuals over time, comparing outcomes between those with a specific exposure (e.g., smoking) and those without. The examples discussed in the script illustrate how cohort studies can be used to measure the risk and risk ratios associated with certain exposures, such as smoking, and their potential health effects.

Outlines
00:00
๐Ÿงฌ Understanding Risk and Cohort Studies

This paragraph introduces the concept of risk by using a hypothetical scenario of 50 people and a disease referred to as 'turning red'. It explains how risk is calculated (17 out of 50 people, resulting in a 34% chance) and acknowledges that not everyone is at the same risk level. The paragraph then delves into the specifics of cohort studies, focusing on smoking as a potential risk factor. It details how risks are calculated for smokers and non-smokers separately and introduces the concept of relative risk, demonstrating that smokers have a 2.4 times higher risk of the disease. The explanation of risk difference, or attributable risk, is also provided, emphasizing the additional risk smoking brings over the baseline.

05:01
๐Ÿผ Smoking During Pregnancy and Low Birth Weight

The second paragraph discusses a real-life cohort study that investigated the impact of smoking during pregnancy on the risk of low birth weight babies. It provides a detailed account of the study's methodology and findings, highlighting the number of pregnant women involved and the division between smokers and non-smokers. The paragraph explains how risk is calculated for each group and introduces the concept of relative risk, showing that smoking during pregnancy nearly doubles the risk of having a low birth weight baby (relative risk of 1.9). The risk difference is also calculated, indicating that smoking increases the absolute risk by 5.75%.

Mindmap
Keywords
๐Ÿ’กRisk
Risk refers to the probability or chance of a specific event occurring, such as developing a disease. In the video, the concept of risk is central to understanding the likelihood of individuals in the cohort study getting sick (the 'disease of turning red') or having low birth weight babies if the mother smoked during pregnancy. It is quantified by dividing the number of people who experienced the event by the total number in the group.
๐Ÿ’กCohort Study
A cohort study is a type of observational study design where a group of individuals with a common characteristic (e.g., smoking) is followed over time to assess their outcomes compared to a non-exposed group. The video uses a hypothetical cohort study to illustrate how risks are calculated for smokers and non-smokers and how these risks can differ between the two groups.
๐Ÿ’กRisk Ratio
The risk ratio, also known as the relative risk, is a measure that compares the risk of an event occurring in an exposed group (e.g., smokers) to the risk in an unexposed group (e.g., non-smokers). It provides insight into how much more or less likely an outcome is in one group compared to another. A risk ratio greater than one indicates an increased risk in the exposed group, while a ratio less than one suggests a protective effect.
๐Ÿ’กExcess Risk
Excess risk, also known as attributable risk, refers to the additional risk of an outcome that can be attributed to a specific exposure (e.g., smoking). It is calculated by subtracting the risk in the unexposed group from the risk in the exposed group. This measure helps to quantify the impact of the exposure on the outcome above and beyond any background risk.
๐Ÿ’กAttributable Risk
Attributable risk is the component of the total risk in a population that can be directly attributed to a specific exposure or risk factor. It is a measure of how much the risk of an outcome would decrease if the exposure were eliminated. In the context of the video, it illustrates the portion of risk for the 'disease of turning red' that is due to smoking.
๐Ÿ’กDisease of Turning Red
In the video, 'disease of turning red' is a hypothetical condition used to illustrate the concept of risk and risk ratios. It serves as a metaphor for a health outcome that the cohort study is investigating, with the color red representing those who have developed the disease.
๐Ÿ’กSmokers and Non-Smokers
Smokers and non-smokers are the two groups used in the video to demonstrate how different exposures can affect the risk of a health outcome. Smokers are considered the exposed group with a potential increased risk, while non-smokers serve as the comparison group assumed to have no increased risk due to smoking.
๐Ÿ’กRisk Difference
Risk difference, also referred to as excess risk, is the absolute difference in the risk of an outcome between two groups (e.g., smokers and non-smokers). It quantifies the additional risk associated with the exposure and is calculated by subtracting the risk of the unexposed group from the risk of the exposed group.
๐Ÿ’กRelative Risk
Relative risk is a term used to describe the ratio of the risk of a particular outcome in one group to the risk in another group. It is a way to compare the risk of an event occurring between two populations. A relative risk greater than one suggests an increased risk in the exposed group, while a relative risk less than one indicates a decreased risk.
๐Ÿ’กLow Birth Weight
Low birth weight refers to babies born with a weight lower than a certain threshold, typically less than 2500 grams (5 pounds, 8 ounces). In the video, low birth weight is used as an outcome to explore the potential impact of maternal smoking during pregnancy on the risk of having a baby with low birth weight.
๐Ÿ’กTwo by Two Table
A two by two table is a statistical tool used to display the distribution of two categorical variables across four possible outcomes. In the context of the video, it is used to organize and calculate risks, risk ratios, and risk differences for smokers and non-smokers in relation to the 'disease of turning red' and low birth weight babies.
Highlights

Understanding risk by tracking a group of 50 people over time for a specific disease.

17 out of 50 people developed the 'disease of turning red', resulting in a risk of 0.34.

The concept of risk and how it varies among individuals based on characteristics like smoking.

Calculating risks separately for smokers and non-smokers to compare disease risk.

Risk among smokers is 0.48, and among non-smokers is 0.2, highlighting the increased risk for smokers.

The risk ratio calculation showing smokers are 2.4 times more likely to get the disease.

Interpreting a risk ratio of oneๆ„ๅ‘ณ็€ๆšด้œฒ็ป„ๅ’Œๆœชๆšด้œฒ็ป„็š„้ฃŽ้™ฉๆฒกๆœ‰ๅทฎๅผ‚.

The risk difference or attributable risk, representing the excess risk introduced by smoking.

A real-world example of a cohort study on smoking during pregnancy and low birth weight babies.

The Royal College of Physicians of Ireland's support for the creation of the video.

The study's findings that smoking during pregnancy nearly doubles the risk of low birth weight babies.

The relative risk of 1.9, indicating an increase in risk due to smoking during pregnancy.

The risk of low birth weight babies increases by 5.7% due to smoking during pregnancy.

The importance of cohort studies in understanding the impact of exposures like smoking on health outcomes.

The simplicity of calculating risk ratios and risk differences using the provided method.

The practical application of these calculations in public health and medical research.

Transcripts

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Health RisksSmoking ImpactDisease RatesCohort StudyRisk RatioExcess RiskPublic HealthPreventive MeasuresMedical ResearchLifestyle Factors