How do statistical organizations define age periods for children?

To help understand data about children – such as child health and mortality – statistical organizations classify the ages of babies and children in a more standardized way.

The World Health Organization (WHO) and United Nations Inter-agency Group for Child Mortality Estimation (UN IGME), for example, use the same definitions for various stages of infanthood, childhood, and adolescence.

I have shown these definitions in the visualization below.

Many countries also use the same definitions for their national statistics, but this is not always the case.

In the sections below, I’ve included summaries of how different stages are defined.

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Infants

As you can see in the visualization, ‘infants’ are defined as those under one year of age.

Within this age period, there are several categories:

These definitions are used consistently by the WHO, UN IGME, and IHME.¹

Children and adolescents

In contrast, the term ‘children’ is often used inconsistently and describes children of different age ranges.

To avoid confusion, statistical organizations tend to use the term ‘under-5’s’ to describe children under 5 years of age.²

The World Health Organization (WHO) and United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) additionally define adolescents as those aged 10 to 19.³ But definitions for adolescents differ widely and sometimes include people up to much older ages.

Miscarriages and stillbirths

Age periods for fetuses – which are referred to in statistics on miscarriages and stillbirths – are often defined inconsistently between countries and statistical organizations.

For example, the WHO defines miscarriage as the spontaneous loss of pregnancy before 28 weeks of completed gestation.⁴

In contrast, the Institute for Health Metrics Evaluation (IHME) defines miscarriage as the “spontaneous loss of pregnancy before 24 weeks of gestation with complications requiring medical care.”⁵

Definitions of stillbirths also vary.

For example, the International Classification of Diseases 11th Revision (ICD-11) defines stillbirths as babies born with no signs of life at 22 or more completed weeks of gestation. They also have two sub-categories of stillbirths: ‘early gestation stillbirth’ (at 22 to 27 completed weeks of gestation) and ‘late gestation stillbirth’ (at 28 or more completed weeks of gestation).

In contrast, the WHO and UN IGME define stillbirths as those at 28 or more completed weeks of gestation, which corresponds to what the ICD-11 calls late gestation stillbirths.⁶

Due to differences in definitions, miscarriages and stillbirths are not shown in the chart.

Saloni Dattani (2023) - “How do statistical organizations define age periods for children?” Published online at OurWorldinData.org. Retrieved from: 'https://ourworldindata.org/how-do-statistical-organizations-define-age-periods-in-children' [Online Resource]

@article{owid-how-do-statistical-organizations-define-age-periods-in-children,
    author = {Saloni Dattani},
    title = {How do statistical organizations define age periods for children?},
    journal = {Our World in Data},
    year = {2023},
    note = {https://ourworldindata.org/how-do-statistical-organizations-define-age-periods-in-children}
}

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