The calculation of the rate must be based on a certain number of absolute numbers.

There is a time unit, which requires observation over a period of time and cannot be obtained from a single observation.

The numerator and denominator should represent the same group of people. If the numerator is qualified (such as age, etc.), the denominator should also be qualified

Commonly used frequency indicators include morbidity, mortality, etc.

The numerator and denominator are separate from each other, do not overlap with each other, and do not tolerate each other.

It is an indicator that compares the size of two independent events, indicating that event A is a multiple or percentage of event B.

No time unit, comparison is made between specific groups of people and specific time points.

In actual use, the units of the two events can be the same or different (such as the ratio of the number of medical staff to the number of beds in a hospital)

Commonly used ratios include sex ratio, standardized death ratio, relative risk, odds ratio, etc.

The units of the numerator and denominator are the same, and the numerator is included in the denominator.

No time unit, comparison is made at a specific time, and is the result of an observation

It is a static indicator, indicating the existence status of each part of something within a certain period of time.

The sum of the values ​​of each part of the composition ratio is 1 or 100%

Commonly used composition ratios include prevalence rate, infection rate, positivity rate, etc.

Describe the distribution of diseases and reflect the degree of impact of diseases on population health

Explore the incidence factors of the disease and propose etiological hypotheses by exploring the incidence rates of different groups of people.

Evaluate the effectiveness of control measures

onset time

Observation time

Number of new cases*

Exposed population*

Used to measure the frequency of new cases in a small area and in a short period of time, in months, weeks, days or an epidemic period as the time unit

Chances of developing disease can be accurately measured based on exposure

Often used to describe outbreaks of food poisoning, occupational poisoning and infectious diseases

When the incidence and course of a disease in a certain place remain stable for a long period of time, the following relationship exists between the prevalence, incidence and course: Prevalence rate P = incidence rate I × disease duration D

Primary case and onset time

Number of susceptible persons among contacts

Number of second-generation cases that occurred during the observation period

Calculate exposure time on an individual basis

Life table method to calculate exposure time

Calculate the number of exposed persons based on the average number of people: Average number of people × number of years of observation

The death rate from all causes is an unadjusted rate known as the crude death rate

When comparing the mortality rates of different groups in different regions, due to the different composition of the population, direct comparison cannot be made, and standardized mortality rates must be used.

The mortality rate calculated according to the type of disease, age, gender, occupation or race is called the death rate. When calculating the death rate, the denominator must be the population corresponding to the numerator

Infant mortality rate (IMR) refers to the ratio of the number of infant deaths within one year of age to the number of live births in the year, generally expressed as a rate per thousand.

The under-5 mortality rate refers to the ratio of the number of deaths of children under the age of 5 (including infant deaths) in a given year to the number of live births in the same year.

Maternal mortality rate refers to the ratio of the number of maternal deaths in a given year to the number of live births in the same year. Often expressed in parts per 10,000 or parts per 100,000

Using a specified standard population composition to eliminate differences in population composition indicators (such as age, gender, etc.) in different regions is called the standardization method. The rate calculated after correction for standard population composition is called the standardized rate (standardized mortality or morbidity rate)

Comparison of mortality rates between places A and B

The ratio of the number of deaths from a certain disease to the total number of deaths in the same period

application

A commonly used indicator to measure the mortality risk of a population in a certain area during a certain period.

Reflects the health status of the population and the level of health care work in a region at different times

Can provide scientific basis for local health care needs and planning

Death rates can be used to explore causes and evaluate prevention and treatment measures

The case fatality rate indicates the probability of death from a confirmed disease. It indicates the severity of the disease and also reflects the medical level and diagnostic capabilities (when the case fatality rate is used as an indicator to evaluate the medical level of different hospitals, attention should be paid to the severity of the conditions of patients admitted to different hospitals and the medical treatment of the hospital. (Facility conditions and other factors)

It is mostly used for acute diseases with short duration and less often for chronic diseases.

Can obtain more complete population data, morbidity and mortality data

Can better reflect the impact of the natural environment on the regional distribution of diseases

Sometimes it can reflect the common or unique cultural traditions, customs and genetic traits of the residents.

The distribution of some diseases is strictly regional within a country

Some diseases have a wide regional distribution, but their incidence rates can show large differences in different regions.

Related to the uneven distribution of elements on the earth’s surface

It is related to the uneven distribution of intermediate hosts and vector insects of the disease.

It is related to factors such as residents’ customs and habits, religious beliefs, socioeconomic culture, health level and genetics.

Also known as an outbreak or epidemic, it refers to a sudden increase in the number of cases of a certain disease in a collective or fixed population in a short period of time.

The speed at which the incidence peaks and the length of the epidemic period are related to the infectiousness of the disease, the length of the incubation period, the proportion of susceptible people in the population at the beginning of the epidemic, and the population density.

Refers to an outbreak

time, space, crowd concentration

Many patients with the same symptoms occur

Mostly caused by short-term exposure of many people to the same pathogenic agent

Due to different incubation periods, the onset of disease occurs first and later, but most cases occur between the shortest and longest incubation periods.

The phenomenon that the frequency of disease increases in a certain season is called seasonality

Strictly seasonal

seasonal increase

No seasonality

Seasonal incidence peak

The occurrence of acute infectious diseases has a certain seasonality

Chronic infectious diseases generally do not have obvious seasonal peaks in incidence

Some non-communicable diseases occur seasonally, such as bronchial asthma and cerebrovascular disease and stroke caused by pollen.

Disease epidemics occur at regular intervals, which is called periodicity (Mainly for infectious diseases, epidemics occur every few years)

Disease transmission mechanisms are easy to implement and can spread quickly as long as there are enough susceptible people.

This type of disease can form a relatively strong immunity after the disease. The length of time the population's immunity level lasts after the epidemic determines the time between epidemics of the disease.

The increase in newborns and the rate of accumulation of susceptible individuals also determine the interval between epidemics.

Pathogen mutation and mutation speed

It refers to the morbidity, mortality, clinical manifestations, pathogen types and hosts of the disease over a long period of time (usually a few years, ten years or decades) as human living conditions change and medical technology changes. significant changes due to progress and changes in natural conditions

Effect of observation time on results

Whether there is any significant progress in treatment measures during the observation period

Explaining long-term variation in chronic disease

Accuracy of morbidity and mortality data

The most important factor in population distribution, the incidence/death of almost all diseases are related to age

The incidence of chronic diseases tends to increase with age, while the incidence of acute infectious diseases tends to decrease.

Reason for the difference

Analysis method of disease age distribution

e.g. Age-adjusted lung cancer mortality rate among white men over 40 years old in the United States Black line: cross-sectional analysis (specific time) Red line: birth cohort analysis (people born in the same generation)

Infectious diseases that are easy to spread and have the ability to consolidate immunity after illness mostly have a high incidence among children. Such as measles, whooping cough, chickenpox

Some infectious diseases with a large number of latent infections are rare in adults. Such as Japanese encephalitis, poliomyelitis, meningococcal meningitis, etc.

Even the same disease can show differences in age distribution due to different prevalent types.

The risk of most cancers increases with age. However, leukemia often attacks teenagers, and liver cancer is more common in middle-aged and middle-aged people.

The incidence of cardiovascular disease also increases with age

History of disease epidemics often affects age distribution

The incidence of some infectious diseases, such as rat hemorrhagic fever and schistosomiasis, is higher among young adults. This is mainly due to the fact that young adults have more opportunities to be exposed to pathogens.

Vaccination can change the age distribution of disease onset. For example, after vaccination with diphtheria toxoid and measles vaccine, the age of onset of both diseases has shifted to older people.

Is a high-risk group for infectious disease outbreaks

It is the link between infectious areas and non-epidemic areas.

Play a non-negligible role in spreading diseases

Adding difficulty to the implementation of planned immunization for children