Epidemiology Concepts and Research Methods

The number of susceptible individuals at the beginning of the outbreak period is used to calculate the probability or risk of illness during an outbreak. This denominator represents the total population at risk.

A crossover randomized trial involves participants receiving different treatments in a sequential order. The washout period ensures that the effects of the first treatment fade before the second treatment is administered. An insufficient washout period can lead to residual effects from the earlier treatment, potentially impacting the results of the second treatment.

Non-adherence to a study protocol, where participants do not follow the assigned treatment plan, can significantly affect the results of a clinical trial. It can underestimate the treatment effect if those discontinuing are more likely to improve with the treatment.

Randomization aims to balance known and unknown factors between groups, reducing bias in a clinical trial. Randomization helps ensure that the groups are comparable.

Loss to follow-up in a clinical trial occurs when participants withdraw from the study before its completion, potentially affecting the results.

Non-adherence can impact a clinical trial's results by influencing the outcome estimate of the treatment effect. Participants not following the treatment plan might not experience the intended effects, leading to an inaccurate assessment of the treatment's efficacy.

Randomization in a clinical trial is a process of assigning participants to groups randomly. This helps balance the known and unknown factors that might influence the outcomes. This reduces the risk of bias, strengthening the reliability of the study findings.

Double-blinding in a clinical trial involves ensuring that neither the participants nor the researchers know who is receiving the real treatment and who is receiving the placebo. This helps prevent bias in how the data is collected and interpreted.

A measure of the proportion of individuals in a population with a specific disease at a given point in time.

A measure of the number of new cases of a disease that occur in a population over a specified period of time.

The rate at which new cases of a disease occur in a population over a specified period of time.

A measure of the proportion of individuals in a population who develop a disease over a specified period of time.

A process of combining the results of multiple studies to generate a single result.

A study design comparing the exposure status of cases to the exposure status of controls.

The use of multiple data sources to validate findings.

A method to address potential confounding bias by comparing the exposure status of cases to their own past exposure status.

The proportion of individuals in a population who are protected from disease due to herd immunity, even if they haven't been vaccinated themselves. This indirect protection occurs because a lower proportion of susceptible individuals means the disease has less opportunity to spread.

The ability of a test to correctly identify individuals with the disease. It is calculated as the number of true positives divided by the total number of individuals with the disease.

The ability of a test to correctly identify individuals without the disease. It is calculated as the number of true negatives divided by the total number of individuals without the disease.

The probability that an individual who tests positive for a disease actually has the disease. It is influenced by the prevalence of the disease in the population being tested.

The proportion of individuals who test positive for a disease who actually have the disease. It is calculated as the number of true positives divided by the total number of individuals who test positive.

The proportion of individuals who test negative for a disease who actually do not have the disease. It is calculated as the number of true negatives divided by the total number of individuals who test negative.

The number of individuals with the disease who are incorrectly classified as not having the disease. It indicates the test's failure to detect the disease.

The number of individuals without the disease who are incorrectly classified as having the disease. It indicates the test's tendency to wrongly diagnose the disease.

Sensitivity measures the proportion of people with the disease who test positive. Specificity measures the proportion of people without the disease who test negative. A higher sensitivity helps correctly identify more people with the disease, while a higher specificity helps correctly identify more people without the disease.

This type of bias occurs when participants who choose to be screened are healthier than those who don't, potentially skewing the results because it's not a true reflection of the general population.

Primary prevention aims to prevent the onset of a disease altogether, before it occurs. This can involve factors like healthy lifestyle choices, vaccinations, and preventive screenings.

One limitation of Mendelian randomization studies is that they can only be used to study certain traits. They cannot be used to examine all exposures because they require a genetic variant linked to the exposure.

A non-randomized study where people who choose to be screened might be healthier than those who don't, making the results unreliable. The difference in health might be related to the screening itself, not just the disease.

A non-randomized study where factors that influence both screening and disease outcome can make it hard to determine the true effect of screening.

A non-randomized study where screening might make the survival time seem longer, even if the actual course of the disease hasn't changed.

A non-randomized study where the participants are not representative of the overall population being screened. This can lead to inaccurate results, as the study findings may not apply to everyone.

The sensitivity of a test describes its ability to correctly identify individuals who actually have the condition being tested for. It's the proportion of people with the disease who test positive.

A vaccine's efficacy measures how well it protects against the disease. An 80% efficacy means vaccinated individuals are 80% less likely to get sick compared to unvaccinated people.

In a case-control study, we compare the exposure history of people with a disease (cases) to those without the disease (controls). If the condition is rare, the odds ratio from this study approximates the risk ratio we would get from a cohort study.

An odds ratio compares the odds of exposure in cases to the odds in controls. If the odds ratio is 1.53, the odds of developing the outcome are 1.53 times higher for those with the exposure.

Randomization ensures each participant has an equal chance of being assigned to either group, aiming to balance known and unknown factors that might influence the results. This helps to make the groups as similar as possible.

Clinical equipoise refers to the ethical principle that a new treatment should be tested only when there is genuine uncertainty about which treatment is better. Both treatment and control groups should have a reasonable chance of benefiting.

Case-control studies often face challenges in finding and selecting appropriate controls that match the cases closely, to ensure the study results are not biased by differences between the groups.

A type of bias that occurs when a third factor is associated with both the exposure and the outcome. This third factor can make it appear as though the exposure is causing the outcome, when in reality, it is the third factor that is causing both.

A type of bias that occurs when the exposure or outcome is measured inaccurately and the errors are not random, but are related to the exposure or outcome.

When the measure of association is biased towards the null, it means that the association between the exposure and the outcome is underestimated. This can happen when there is non-differential misclassification of the exposure status because the misclassification is equal in both groups. That is, an equal number of exposed and unexposed individuals are miscategorized.

It is ethical to enroll patients in a randomized controlled trial (RCT) even if there is uncertainty about the drug's effectiveness because the RCT design reduces bias, minimizing the uncertainty of the drug's efficacy. Ethical research includes the need to balance ensuring patient well-being with generating new medical knowledge.

A confounder should not be a consequence of the exposure because it should be independent of the exposure. If the confounder is caused by the exposure, then it is on the causal pathway between the exposure and the outcome, not a confounder.