The rate at which a new event occurs in a population. The numerator is the number of new events that occur in a defined population. The denominator is the population at risk of experiencing this event during this period, which can also be expressed as "person-time." 

Incidence Denisty is a rate. It is not a proportion. 

Also called Retrospective Study. It is an observational study of people with the disease (or other outcome) and a comparrison (control) group of people without the disease. It looks back in time. 

It can also be called an analytic or experimental study.

Also known as a prevelance study, or a descriptive study. It provides a snapshot at a certain point in time. It looks at disease and exposure status being meausred at the same time in a certain population, such as obseity and TV watching. 

It does not require follow-up and is representative of a large population. But, you do not know from it if the exposure caused the disease or not, since they are being studied at the same time. 

A summary rate based on the actual number of events in a population over a given period of time. 

For example, it is the total number of deaths to people living in a certain area divided by the total population of people in that same area (in the same time period), and then multiplied by 100,000.

Also called an ecological bias or aggregation bias.

 Failure in reasoning that arises when an inference is made about an individual based on aggregate data for a group.

For example, if a study shows that people who wear glasses have above average intelligence, assuming that everyone who wears glasses is intelligent is an example of ecological fallacy. Applying an ecological fallacy occurs when group data is used to draw conclusions about individuals

Also called attributable fraction, and attributable risk percent.

It is the proportion of cases in which the exposure has played a causal role in disease development.

It is the proportion of all cases that can be attributed to a certain exposure. It usually is shown in a cohort study, where people are brought together based on exposure to something and followed over a period of time.

Lead time is the length of time between the detection of a disease and its usual clinical presentation and diagnosis. Lead time bias is overestimation of survival time, due to shifting back too far in the starting point for measuring survival that happens when diseases, such as cancer, are detected early (due to good screening).

It is the systematic error of increased survival from detecting disease in an early stage.

Wrongly classifying a person, a value or an attribute into a certain category. 

Nondifferential misclassifcation is is when the probability of misclassification is the same in all study groups.

Differential misclassification is when the probability of misclassification varies within study groups. 

This is a form of information bias.

A measurement combining the number of people and their time contribution in a study. This measure is most often used as denominator in incidence rates (how fast the disease is spreading). It is the sum of individual units of time that the persons in the study population have been exposed or at risk to the conditions of interest.

Person-Time: The amount of at risk time each person contributes

• If a person develops the disease on day 2, they contribute 1.5 person-days during which they were at risk for developing disease
• If a person is at risk for 30 days and does not contract the disease, they contribute 30 person-days at risk
• Combined, these two people contributed 31.5 person-days at risk

The number of people with the disease or attribute at a certain point in time.

Prevelence does not look at risk.

Primary prevention prevents the disease before it even happens (ie, banning dangerous chemicals so that no one is exposed, providing health education, immunization)

Secondary prevention aims to reduce the impact of the disease/injury once it's happened or attempting to detect the disease before it happens (ie, mammograms before breast cancer, modifying work so that injured workers can return to work, daily aspirin to avoid heart problems)

Tertiary prevention helps people manage the impact of long-term illnesses/disease (ie, rehab programs, chronic disease management) -- this "softens" the impact

Swimming hole example:

Primary prevention: keeping chemicals out of the swimming hole

Secondary prevention: Having lifeguards check swimmers for rashes after they swim

Tertiary prevention: Setting up support programs for people to learn how to deal with their persistent rashes

Also called "relative risk" and "risk ratio"

The ratio of the rate in the exposed population to the rate in the unexposed population.

To find it out, you divide the cumulative incidence in the exposed to the cumultative incidence in the unexposed.

The number you get by dividing one quantity by another; rates, percentages, and proportions are subsets.

For example, the male to female ratio in your class.

The important difference between a proportion and a ratio is that the numerator of a proportion is included in the population defined by the denominator, but this is not necessarily true for a ratio. 

Also called Temporal Trends.

Changes over long periods of time, such as years or decades. 

Example: Decline of TB mortality

Females have a higher morbidity rate in the US than males.

This is known as the "female paradox." Women have higher morbidity rates than males but lower mortality rates.

The numerator for case fatality is “number of individuals dying during a specified period of time from the disease of interest” and the denominator is “number of persons with the disease of interest.” 

If 100 people ate spinach with e.coli, and 15 died, then numerator is 15 and the denominator is 100. You could say that 150 per 1,000 people died.

That is the case fatality.

Specificity is the ability of a test to correctly determine who does not have a disease (true negative rate).

Sensitivity is the ability of a test to correctly determine who does have the disease (true positive rate).

The study of the distribution and determinants of health and disease in populations. 

It is the study of the distribution and determinants of health-related states or events in specified populations and the appication of this study to control health problems.

It is the study of diesease in populations.

1. Common source (a group of people are exposed to a common agent, either over a brief period of time or over a long period of time)

2. Propagated (spreads gradually from person to person)

3. Mixed epidemic (common source and from person to person)

Type 1 Error is when we reject the null hypothesis when it is true.

Type II Error is when we do not reject the null hypothesis when it is false.