Table 3.3 Frequently Used Measures of Morbidity
| Measure | Numerator | Denominator |
| Incidence proportion (or attack rate or ... | Number of new cases of disease during sp ... | Population at start of time interval |
| Secondary attack rate | Number of new cases among contacts | Total number of contacts |
| Incidence rate (or person-time rate) | Number of new cases of disease during sp ... | Summed person-years of observation or av ... |
| Point prevalence | Number of current cases (new and preexis ... | Population at the same specified point i ... |
How do you calculate attack rate?
- Where A is the attack rate
- #NC is the number of cases of a disease in people exposed to a specific event
- #PE is the number of people exposed to the specific event
What is difference between attack rate and incidence rate?
We would calculate the incidence rate ratio (often abbreviated IRR) as:
- IRR = Incidence rate among smokers / Incidence rate among non-smokers
- IRR = (7/100) / (1.5/100)
- IRR = 4.67
What is the current attack rate of the disease?
Overall attack rate is the total number of new cases divided by the total population. A food-specific attack rate is the number of persons who ate a specified food and became ill divided by the total number of persons who ate that food, as illustrated in the previous potato salad example.
What is the formula for attack rate?
- Total Attack = The total attack stat shown on your Champion page, any attack gained from an aura is also accounted for here, so x% of base Attack + shown ...
- Crit Multiplier is 100% + Crit Damage % assuming you always crit.
- Skill Multiplier is looked up from a Data Mined Source
- Increase damage provided by books is found on the ability description
What is attack rate in public health?
attack rate a form of incidence that measures the proportion of persons in a population who experience an acute health event during a limited period (e.g., during an outbreak), calculated as the number of new cases of a health problem during an outbreak divided by the size of the population at the beginning of the ...
Is attack rate a type of incidence rate?
An attack rate is not an incidence rate. It is actually a risk (also called incidence proportions), and the time contribution of each individual is not included in the denominator.
What are the two types of attack rates?
There are two types of attack rate: primary attack rate and secondary attack rate. An attack rate is also an incidence rate (we discussed this in Study 1 of the SARS exercise). An attack rate is used when the occurrence of disease among a population at risk increases dramatically over a short period of time.
Is attack rate the same as risk ratio?
A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2.
What is meant by attack rate?
In the outbreak setting, the term attack rate is often used as a synonym for risk. It is the risk of getting the disease during a specified period, such as the duration of an outbreak. A variety of attack rates can be calculated. Overall attack rate is the total number of new cases divided by the total population.
How do you calculate an attack rate example?
The overall attack rate refers to the total number of new cases divided by the total population: Attack Rate (%) = No. of new cases of disease during time interval / Population at risk at start of time interval x 100.
What is an attack rate and why do Epidemiologists use them?
Attack rates typically are used in the investigation of acute outbreaks of disease, where they can help identify exposures that contributed to the illness (e.g., consumption of a specific food). The attack rate is calculated as the number of people who became ill divided by the number of people at risk for the illness.
How do you calculate rate in epidemiology?
Let p represent the incidence proportion or prevalence proportion of disease and o represent the odds of disease. Thus, odds o = p / (1 – p). Reporting: To report a risk or rate “per m,” simply multiply it by m. For example, an incidence proportion of 0.0010 = 0.0010 × 10,000 = 10 per 10,000.
What is the difference between prevalence rate and incidence rate?
Incidence is a measure of the number of new cases of a characteristic that develop in a population in a specified time period; whereas prevalence is the proportion of a population who have a specific characteristic in a given time period, regardless of when they first developed the characteristic.
What does a risk ratio of 0.75 mean?
2c) A risk ratio of 0.75 means there is an inverse association, i.e. there is a decreased risk for the health outcome among the exposed group when compared with the unexposed group. The exposed group has 0.75 times the risk of having the health outcome when compared with the unexposed group.
What are the three components of the epidemiology triangle?
Causation. A number of models of disease causation have been proposed. Among the simplest of these is the epidemiologic triad or triangle, the traditional model for infectious disease. The triad consists of an external agent, a susceptible host, and an environment that brings the host and agent together.
What is the difference between prevalence rate and incidence rate?
Incidence is a measure of the number of new cases of a characteristic that develop in a population in a specified time period; whereas prevalence is the proportion of a population who have a specific characteristic in a given time period, regardless of when they first developed the characteristic.
Is incidence and prevalence the same?
Prevalence differs from incidence proportion as prevalence includes all cases (new and pre-existing cases) in the population at the specified time whereas incidence is limited to new cases only.
How do you find the incidence rate?
How Do You Calculate Person-Time Incidence Rates? Person-time incidence rates, which are also known as incidence density rates, are determined by taking the total number of new cases of an event and dividing that by the sum of the person-time of the at-risk population.
How does incidence rate work?
An incidence rate describes how quickly disease occurs in a population. It is based on person-time, so it has some advantages over an incidence proportion. Because person-time is calculated for each subject, it can accommodate persons coming into and leaving the study. As noted in the previous example, the denominator accounts for study participants who are lost to follow-up or who die during the study period. In addition, it allows enrollees to enter the study at different times. In the NHANES follow-up study, some participants were enrolled in 1971, others in 1972, 1973, 1974, and 1975.
What is the numerator of the incidence rate?
Similar to the incidence proportion, the numerator of the incidence rate is the number of new cases identified during the period of observation. However, the denominator differs. The denominator is the sum of the time each person was observed, totaled for all persons.
What is the difference between prevalence and incidence?
Prevalence and incidence are frequently confused. Prevalence refers to proportion of persons who have a condition at or during a particular time period, whereas incidence refers to the proportion or rate of persons who develop a condition during a particular time period.
How is the incidence rate calculated?
A person-time rate is generally calculated from a long-term cohort follow-up study, wherein enrollees are followed over time and the occurrence of new cases of disease is documented. Typically, each person is observed from an established starting time until one of four “end points” is reached: onset of disease, death, migration out of the study (“lost to follow-up”), or the end of the study. Similar to the incidence proportion, the numerator of the incidence rate is the number of new cases identified during the period of observation. However, the denominator differs. The denominator is the sum of the time each person was observed, totaled for all persons. This denominator represents the total time the population was at risk of and being watched for disease. Thus, the incidence rate is the ratio of the number of cases to the total time the population is at risk of disease.
What is incidence proportion?
Incidence proportion is a measure of the risk of disease or the probability of developing the disease during the specified period. As a measure of incidence, it includes only new cases of disease in the numerator. The denominator is the number of persons in the population at the start of the observation period.
What does low prevalence mean?
Conversely, low prevalence might indicate low incidence, a rapidly fatal process, or rapid recovery.
What is the denominator of the person time rate?
The denominator of the person-time rate is the sum of all of the person-years for each study participant. So, someone lost to follow-up in year 3, and someone diagnosed with the disease in year 3, each contributes 2.5 years of disease-free follow-up to the denominator.
What is the measure of association that quantifies the relationship between an exposure with two categories and health outcome?
An odds ratio (OR) is another measure of association that quantifies the relationship between an exposure with two categories and health outcome. Referring to the four cells in Table 3.15, the odds ratio is calculated as
What does a risk ratio of 1.0 mean?
A risk ratio greater than 1.0 indicates an increased risk for the group in the numerator, usually the exposed group. A risk ratio less than 1.0 indicates a decreased risk for the exposed group, indicating that perhaps exposure actually protects against disease occurrence.
What is risk ratio?
A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2.
What is the measure of association?
A measure of association quantifies the relationship between exposure and disease among the two groups. Exposure is used loosely to mean not only exposure to foods, mosquitoes, a partner with a sexually transmissible disease, or a toxic waste dump, but also inherent characteristics of persons (for example, age, race, sex), ...
Can odds ratios be calculated from case control?
As a result, risks, rates, risk ratios or rate ratios cannot be calculated from the typical case-control study. However, you can calculate an odds ratio and interpret it as an approximation of the risk ratio, particularly when the disease is uncommon in the population.
What is attack rate?
Attack rate. In epidemiology, the attack rate is the percentage of an at-risk population that contracts the disease during a specified time interval. It is used in hypothetical predictions and during actual outbreaks of disease.
What is an at risk population?
An at-risk population is defined as one that has no immunity to the attacking pathogen which can be either a novel pathogen or an established pathogen. It is used to project the number of infections to expect during an epidemic. This aids in marshalling resources for delivery of medical care as well as production of vaccines and/or anti-viral ...
What is attack rate?
Attack rate is a term used in epidemiology, usually in the setting of outbreaks, to define the risk of contracting a disease during a specified period (i. e. outbreak duration). The overall attack rate refers to the total number of new cases divided by the total population:
What is specific attack rate?
Specific attack rates may be defined in relation to age, gender, residence, occupation or other factors. Two attack rates may be compared to each other as a relative risk (division) or as a risk difference (subtraction).
