Global Estimates of Modern Slavery: Estimation Method

Modern slavery is the very antithesis of social justice and sustainable development. It covers a set of specific legal concepts including forced labour, concepts linked to forced labour, i.e., human trafficking, debt bondage, slavery and slavery-like practices, and forced marriage. The Global Estimates of Modern Slavery: Forced Labour and Forced Marriage indicates there are 50 million people in situations of modern slavery on any given day from 2017 to 2021, either forced to work against their will or in a marriage that they were forced into. This number translates to nearly one of every 150 people in the world. The estimates also indicate that situations of modern slavery are by no means transient – entrapment in forced labour can last years, while in most cases forced marriage is a life sentence.

The Global Estimates were developed by the International Labour Organization (ILO), Walk Free, and the International Organization for Migration (IOM). They are derived from multiple data sources, including about 70 nationally representative household surveys and the CTDC dataset on victims of trafficking. The CTDC dataset comprises cases of trafficking for labour exploitation and sexual exploitation. The Global Estimates are based on cases of forced labour and forced marriage occurring during the five-year reference period from 2017 to 2021. The forced labour estimates include two main typologies of forced labour:

Privately-imposed forced labour refers to forced labour in the private economy imposed by private individuals, groups or companies. It includes forced labour exploitation and forced commercial sexual exploitation.
State-imposed forced labour refers to forced labour imposed by State authorities.

Forced labour of adults and children is estimated for each typology of forced labour.

Several data sources and methods are used to estimate different components of modern slavery. For example, we estimate forced commercial sexual exploitation of adults, commercial sexual exploitation of children, and forced labour exploitation of children using information from national surveys as well as the CTDC dataset. We use a statistical measure called the odds ratio.

In this data story, we will briefly explain what odds ratio is and how the estimates are computed using the CTDC data and household survey. If you’re interested in more details, please refer to the methodology report (forthcoming).

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What is odds ratio?

Despite efforts in data collection (including asking surveyed individuals about their family networks), reliable data on the entire population subjected to modern slavery is not available.

Survey data cannot capture an adequate number of cases for the estimation of certain populations – namely, children in modern slavery and individuals subjected to forced commercial sexual exploitation. It is challenging to interview a representative sample of these populations due to the ethical issues that arise when interviewing children, as well as the sensitivities and stigma that may be associated with forced commercial sexual exploitation and modern slavery of children.

For these reasons, the survey data are deemed to be sufficiently reliable for measuring adult forced labour exploitation and forced marriage, but not sufficiently reliable for measuring forced commercial sexual exploitation and forced labour exploitation of children. Therefore, odds ratio is used to extrapolate the prevalence of these hidden populations from the CTDC data to complement the survey data.

How is the CTDC dataset used to compute the global estimates?

To estimate the odds of being subjected to forced commercial sexual exploitation relative to being subjected to forced labour exploitation (model 1), we apply a logit model regressing the type of exploitation (forced commercial sexual exploitation versus forced labour exploitation) (as the dependent or Y variable) against sex, majority status, and an interaction term of sex and majority status (as the independent or X variables). See the methodology report (forthcoming) for more information.

To estimate the odds of being victims of forced labour exploitation as a child relative to that of an adult (model 2), we apply a logit model regressing the proportion of child victims of forced labour exploitation versus the proportion of adult victims of forced labour exploitation (as the dependent or Y variable) against sex (as the independent or X variable). We do the same for sexual exploitation, as a child rather than as an adult.

The odds ratios are then applied to the corresponding estimates of forced labour exploitation of adults derived from the national surveys to estimate forced labour exploitation of children, forced commercial sexual exploitation of adults, and commercial sexual exploitation of children.

An example

In model 1 (below), we use a logit model to calculate the odds ratio of falling victim to forced commercial sexual exploitation relative to being subjected to forced labour exploitation in the region of exploitation r.

$https://latex.codecogs.com/svg.image?ln(\frac{p}{1-p})= \alpha _{r} + \beta_{r} sex + \gamma_{r} majorityStatus + \delta_{r} sex*majorityStatus$

Here is the calculation process for model 1.

Table 1: Calculation of odds ratio from the parameters of the logit model
		(1)	(2)	(3)	(4)	(5)=(1)+(2)+(3)+(4)	(6)=exp(5)
Sex	Majority status	α	β	γ	δ	ln(p/1-p)	Odds ratio
Female=0	Child=0	0.2025	0	0	0	0.2025	1.2244
Female=0	Adult=1	0.2025	0	-0.4658	0	-0.2633	0.7685
Male=1	Child=0	0.2025	0.1040	0	0	0.3065	1.3587
Male=1	Adult=1	0.2025	0.1040	-0.4658	-2.8531	-3.0124	0.0492

Source: Methodology report, forthcoming.

The odds ratios are reported in the last column of the table. They are greater than 1 for children and smaller than 1 for adults. This means that children, boys or girls, are more likely to fall victim to forced commercial sexual exploitation than forced labour exploitation. By contrast, adults, particularly men, are more likely to fall victim to forced labour exploitation than forced commercial sexual exploitation.

Here is a summary of the odds ratio computed for the Global Estimates.

Table 2: Odds ratio computed for the Global Estimates
Model	Group	Odds Ratio
1	Woman	0.7685
1	Man	0.0492
1	Girl	1.2244
1	Boy	1.3587

2	Girl	0.1233
2	Boy	0.0607

Notes: For simplicity, adult female is classified as woman; children female is girl; adult male is man; children male is boy. Source: Methodology report, forthcoming.

To estimate the forced commercial sexual exploitation of adults, let’s use the odds ratio of woman and man as examples. In Table 3 (below), you can see how we compute the estimates. We multiply the estimates of adult forced labour exploitation (obtained from surveys) to the odds ratios of adult forced commercial sexual exploitation relative to adult forced labour exploitation (obtained from the logit model and the CTDC dataset).

Table 3: Global estimation of forced sexual exploitation of adults by sex
Adult forced labour ('000), male	Adult forced labour ('000), female	Adult odds ratio, male	Adult odds ratio, female	Adult forced commercial sexual exploit ('000), male	Adult forced commercial sexual exploit ('000), female
10656	5361	0.0492	0.7685	10656 x 0.0492 = 524	5361 x 0.7685 = 4120

Source: Methodology report, forthcoming.

How can I interpret the odds ratio?

Let’s use the odds ratio of 0.0492 and 0.7685 for males and females as examples.

For men, the odds of being a victim of forced commercial sexual exploitation are 0.05 times lower than being a victim of forced labour exploitation. This means that for every 100 men who were victims of forced labour exploitation, it is likely that 5 other men were victims of forced commercial sexual exploitation.

For women, the odds of being a victim of forced commercial sexual exploitation are 0.77 times lower than being a victim of forced labour exploitation. This means that for every 100 women who were victims of forced labour exploitation, it is likely that 77 other women were victims of forced commercial sexual exploitation.

Main results of the Global Estimates

There are 27.6 million people in situations of forced labour on any given day from 2017 to 2021. This absolute number translates to 3.5 people in forced labour for every thousand people in the world.

Table 4 (below) is a summary table with the Global Estimates that are computed using different data sources and methods. Forced labour exploitation of adults is computed based on national surveys. Forced commercial sexual exploitation of adults and forced labour of children (including forced labour exploitation of children and commercial sexual exploitation of children) are estimated using the odds ratio based on the CTDC dataset.

Table 4: Number and prevalence of persons in modern slavery, by category, sex, age, and national income grouping
		Privately-imposed forced labour excluding FCSE		Forced commercial sexual exploitation (FCSE)		TOTAL PRIVATELY-IMPOSED FORCED LABOUR		State-imposed forced labour		TOTAL FORCED LABOUR (c)		FORCED MARRIAGE		TOTAL MODERN SLAVERY (d)
		No. (a)	‰ (b)	No. (a)	‰ (b)	No. (a)	‰ (b)	No. (a)	‰ (b)	No. (a)	‰ (b)	No. (a)	‰ (b)	No. (a)	‰ (b)
	World	17325	2.2	6332	0.8	23657	3.0	3920	0.5	27577	3.5	21993	2.8	49570	6.4
Sex	Male	11303	2.9	1403	0.4	12706	3.2	3072	0.8	15779	4.0	7060	1.8	22839	5.8
	Female	6022	1.6	4929	1.3	10951	2.8	848	0.2	11798	3.1	14933	3.9	26731	6.9
Age	Adults	16017	2.9	4644	0.9	20661	3.8	3603	0.7	24263	4.5	13020	2.4	37283	6.9
	Children	1308	0.6	1688	0.7	2997	1.3	317	0.1	3314	1.4	8973	3.8	12287	5.2
Income grouping (e)	High income	4065	3.3	1208	1.0	5274	4.3	110	0.1	5384	4.4	1865	1.5	4704	3.8
	Upper-middle income	4490	1.5	2451	0.8	6941	2.4	2025	0.7	8965	3.1	3737	1.3	13842	4.8
	Lower-middle income	6467	2.2	2122	0.7	8590	2.9	326	0.1	8916	3.0	14131	4.8	20945	7.1
	Low income	2301	3.4	551	0.8	2852	4.2	1459	2.1	4311	6.3	2261	3.3	8772	12.8

Notes: (a) Number is expressed in thousands. (b) “‰” denotes cases per 1,000 population. (c) “TOTAL FORCED LABOUR” comprises forced labour exploitation and state-imposed forced labour. (d) “TOTAL MODERN SLAVERY” comprises privately-imposed forced labour, state-imposed forced labour, and forced marriage. (e) “Income grouping” refers to the income group of the country where forced labour occurs. Source: Table 1 of the main report.

While the Global Estimates did not explicitly estimate the prevalence of trafficking in persons, the report underlines those individuals subject to forced labour and forced commercial sexual exploitation, as well as migrant workers, are vulnerable to unscrupulous recruitment and abuse by traffickers.

No region of the world is spared from forced labour. Asia and the Pacific is host to more than half of the global total (15.1million), followed by Europe and Central Asia (4.1 million), Africa (3.8 million), the Americas (3.6 million), and the Arab States (0.9 million).

However, this regional ranking changes considerably when forced labour is expressed in terms of prevalence (i.e., as a proportion of the population). By this measure, forced labour is highest in the Arab States (5.3 per thousand people), followed by Europe and Central Asia (4.4 per thousand), the Americas and Asia and the Pacific (both at 3.5 per thousand), and Africa (2.9 per thousand).

Where are the forced labour?

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Migrant workers face a higher risk of forced labour than other workers. The forced labour prevalence of adult migrant workers is more than three times higher than that of adult non-migrant workers.

Migrant adults in forced labour exploitation are defined as those who are subject to forced labour in a country different from that of their birth.

Migrant workers who are not protected by law or are unable to exercise their rights face a higher risk of forced labour than other workers.

The figure (to the right) makes clear that when migration is irregular or poorly governed, or where recruitment practices are unfair or unethical, migration can lead to situations of vulnerability to forced labour.

National policy and legal frameworks that promote respect for the rights of all migrants at all stages of the migration process, regardless of their migration status, are urgently needed.

The tragedy of children subjected to forced labour demands special urgency. A total of 3.3 million children are in situations of forced labour, accounting for about 12 per cent of all those in forced labour.

The forced labour of children constitutes one component of child labour, which the international community – through Target 8.7 of the Sustainable Development Goals – has committed to ending by 2025.

Notes: The figures below use the numbers expressed in thousands for "TOTAL FORCED LABOUR", which includes persons in forced labour and commercial sexual exploitation, and state-imposed forced labour.

Who are in forced labour?

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ADULTS IN FORCED LABOUR BY MIGRANT STATUS AND SEX

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The methodology underlying the Global Estimates is the product of an ongoing process of refinement made possible by an improved understanding of forced labour and forced marriage and of how best to measure them. Reliable information and statistics on forced labour, forced marriage, and human trafficking are critical to promoting awareness and understanding of the problem, and to informing policy responses. The methodological refinements in measurement, combined with a more balanced geographical coverage in data, mean that the Global Estimates are the most complete and comprehensive to date.

We invite you to read the Global Estimates of Modern Slavery: Forced Labour and Forced Marriage in greater detail. If you’re interested in the estimation methodology, please refer to the methodology report (forthcoming).

Data and Resources

All the tables published in this data story on the Global Estimates of Modern Slavery: Forced Labour and Forced Marriage are available here.

Data and Resources

Resource - GEMS method: Table 1csv
This refers to Table 1 in the data story – calculation of odds ratio from...
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Resource - GEMS method: Table 2 Summary of the odds ratiocsv
This is a summary table containing all the odds ratios based on the CTDC...
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Resource - GEMS method: Table 3csv
This refers to Table 3 in the data story – estimation of forced sexual...
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Resource - GEMS method: Table 4 (or Table 1 of the main report)excel
This refers to Table 1 of the main report.

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Resource - GEMS method: Figure on forced labour by regioncsv
This refers to the figure "Where are the forced labour?" in the data story...
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Resource - GEMS method: Figure on forced labour by majority statuscsv
This refers to the figure "Who are in forced labour?" in the data story.

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Resource - GEMS method: Figure on forced labour by migrant status and sexcsv
This refers to the figure "Prevalence of adults in forced labour...
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Dataset analysis

Regional

Field	Value
Modified	2022-12-05
Release Date	2022-07-13
Identifier	5d5a2784-9ec3-46f9-8830-03b6a210bd8c
License	IOM Terms of Use
Public Access Level	Public

What is odds ratio?

How is the CTDC dataset used to compute the global estimates?

An example

How can I interpret the odds ratio?

Main results of the Global Estimates

Where are the forced labour?

Who are in forced labour?

ADULTS IN FORCED LABOUR BY MIGRANT STATUS AND SEX

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