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🏥 | Prevalence of “mouth pocket” in Japanese children, revealed in the first national epidemiological survey


Prevalence of "mouth pocket" in Japanese children revealed in the first national epidemiological survey

If you write the contents roughly
In addition, there was no regional difference in the prevalence of oral poking.

Niigata University, Ogaki Women's Junior College, and Kagoshima University are the first in Japan to have childhood "mouth pockets" (in technical terms, lip closure failure ... → Continue reading

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Regional differences


Prevalence(Yubyowarai,English: Prevalence) Is static of the disease in the populationfrequencyIt is one of the indexes that represent.EpidemiologyThe prevalence rate is calculated as follows.In epidemiology from the pastPrevalenceWithout expressingPrevalence(Yubyoritsu, Prevalence rate or simply Prevalence).

  • Prevalence =Prevalence/ Size of observation population at risk of disease

Here, the prevalence is the number of people with a specific disease or health condition within a given population at a given point in time.The size of the population is likely to have the disease or health condition at that time.It is a concept different from the prevalence, which is the same notation in English.[1]Of this indexunitIs dimensionless.Since the value is represented by a real number between 0 and 1,percentageIt may be represented by.

back ground

Epidemiology deals with epidemic conditions in biological populations.To quantitatively express the nature of the group率,Proportion,ratioThe concept isMathIt was introduced more and became frequently used as a basic material.


  • There is no clear line between whether an individual is healthy or ill.The index for expressing the frequency of disease in a population has a strong meaning as a material for comparison.
  • There is a study using the prevalence rate.
  • If you want to secureAge structureWith the standard prevalence rate in consideration ofratioTo use.
  • Unlike the dynamic (speed) frequency of illness, it represents the static (dimensionless) frequency.
  • When expressing the frequency of extremely rare diseases,The number of occurrences,PrevalenceIs used.
  • By definition, the distribution of diseases is not expressed.
  • By checking the disease rate for each region and comparing or creating, it is possible to grasp the disease.
  • PrevalencevariableIs an accumulation of the presence or absence of morbidity.From this, the distribution of prevalence in different populations is high when prevalence is high.normal distributionIn addition, if the prevalence is lowPoisson distributionIs approximated to.
  • It is known that the application of statistics can estimate the overall prevalence by examining only a part of the population.This has been applied to save material time resources in many epidemiological studies.

Prevalence in epidemiology

From the past history, in epidemiology,PrevalenceIt is called the prevalence rate (or simply Prevalence if unmistakable, because Prevalence may be translated as prevalence).This is defined below.

a: Number of people with the disease at a given point in time

b: The size of the population at risk for the observation target
However, since it is difficult to accurately grasp the risk population, the entire population of the study area is used as an approximation.

n: In general administrative statistics, a constant is multiplied to express the prevalence per 1000 (n = 3) or 10 (n = 5).

Factors that increase prevalenceFactors that reduce prevalence
  • Long illness
  • Low cure rate and case fatality rate
  • Influx of patients (from other regions)
  • Increase in new patients
  • Outflow of healthy people
  • Increased diagnostic opportunities Increased reports
  • Short duration of illness
  • High cure rate and case fatality rate
  • Outflow of patients (from other areas)
  • Decrease in new patients
  • Influx of healthy people
  • Decrease in diagnostic opportunities (limited) 
  •  Inadequate medical system

Crude morbidity and age-adjusted morbidity

For diseases with significantly different morbidity with age, it is not preferable to simply compare the morbidity of two populations with significantly different age structures.A specific example is cancer.In such cases, in the above-defined morbidity rate (hereinafter referred to as crude morbidity rate), the crude morbidity rate of cancer is higher in the group with many elderly people than in the group with few elderly people.Therefore, even if there is a difference in the crude morbidity between the two populations, it is not possible to distinguish whether the difference is the true difference in morbidity or simply due to the difference in age composition.Therefore, the morbidity rate is calculated for each age group, and the sum of weights for each age group is calculated according to the age composition of the reference population (standard population, which is usually the model population in 60). , Age-adjusted Incidence Rate.

Age classMorbidity by age group

When the constituent age group changes with aging, it may be necessary to look at the age-adjusted morbidity when observing the morbidity over time.


  1. ^ Epidemiology Dictionary XNUMXrd Edition, Japan Public Health Association

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