Movement of people, most often through migration, is a significant part of global integration. Migrants contribute to the economies of both their host country and their country of origin. Yet reliable statistics on migration are difficult to collect and are often incomplete, making international comparisons a challenge.

In most developed countries, refugees are admitted for resettlement and are routinely included in population counts by censuses or population registers. Globally, the number of refugees at end 2010 was 10.55 million, including 597,300 people considered by the United Nations High Commissioner for Refugees (UNHCR) to be in a refugee-like situation; developing countries hosted 8.5 million refugees, or 80 percent of the global refugee population.

Global migration patterns have become increasingly complex in modern times, involving not just refugees, but also millions of economic migrants. But refugees and migrants, even if they often travel in the same way, are fundamentally different, and for that reason are treated very differently under modern international law. Migrants, especially economic migrants, choose to move in order to improve the future prospects of themselves and their families. Refugees have to move if they are to save their lives or preserve their freedom. They have no protection from their own state - indeed it is often their own government that is threatening to persecute them. If other countries do not let them in, and do not help them once they are in, then they may be condemning them to death - or to an intolerable life in the shadows, without sustenance and without rights.
Personal remittances, received (current US$)
Remittance transactions have grown in importance over the past decade. In a number of developing economies, receipts of remittances have become an important and stable source of funds that exceeds receipts from exports of goods and services or from financial inflows on foreign direct investment. But the quality of statistical remittance data is not high. Remittances are a challenge to measure because of their nature. They are heterogeneous with numerous small transactions conducted by individuals through a wide variety of channels: formal channels, such as electronic wire, or through informal channels, such as cash or goods carried across borders. The large number of remittance transactions and the multitude of channels pose challenges to the compilation of comprehensive statistics. The small size of individual transactions means that they often go undetected by typical data source systems, although the aggregate level of transactions may be substantial.

Because of difficulties in obtaining data on informal remittance transactions, the remittance transactions undertaken through informal channels are sometimes not well covered in current balance of payments data. As a result, even though direct measurement of remittances - through transactions reporting or surveys - may be considered preferable if feasible, some countries instead combine different sources and estimation methods to achieve better coverage, by using direct measurements where practical and supplemented estimates where they are not. Model-based approaches are used in some countries as they are flexible. Compilers can design models to fill gaps in data sources or to provide global totals.

However, only reliable input data can lead to sound estimates, regardless of the sophistication of an estimation method or econometric model. Indirect data are converted to remittance estimates using a set of assumptions. These assumptions should be plausible, but it is often not possible to test or verify these assumptions and also the results in practice.
Personal remittances comprise personal transfers and compensation of employees. Personal transfers consist of all current transfers in cash or in kind made or received by resident households to or from nonresident households. Personal transfers thus include all current transfers between resident and nonresident individuals. Compensation of employees refers to the income of border, seasonal, and other short-term workers who are employed in an economy where they are not resident and of residents employed by nonresident entities. Data are the sum of two items defined in the sixth edition of the IMF's Balance of Payments Manual: personal transfers and compensation of employees. Data are in current U.S. dollars.
The two main components of personal remittances, "personal transfers" and "compensation of employees", are items in the balance of payments (BPM6) framework. Both of these standard components are recorded in the current account. 
"Personal transfers", a new item in the Balance of Payments (BPM6) represents a broader definition of worker remittances. Personal transfers include all current transfers in cash or in kind between resident and nonresident individuals, independent of the source of income of the sender (irrespective of whether the sender receives income from labor, entrepreneurial or property income, social benefits, and any other types of transfers; or disposes assets) and the relationship between the households (irrespective of whether they are related or unrelated individuals).

Compensation of employees refers to the income of border, seasonal, and other short-term workers who are employed in an economy where they are not resident and of residents employed by nonresident entities. Compensation of employees represents remuneration in return for the labor input to the production process contributed by an individual in an employer-employee relationship with the enterprise. Compensation of employees is recorded gross and includes amounts paid by the employee as taxes or for other purposes in the economy where the work is performed. Compensation of employees has three main components: wages and salaries in cash, wages and salaries in kind, and employers' social contributions.