Population researchers have called on governments to collect and share more information about migration to keep better track of the millions of people who move from one country to another each year.
Record numbers of people have fled the ongoing conflict in Syria, bringing global attention to international migration.
Professor James Raymer from The Australian National University (ANU) said it was impossible to accurately determine how many people were moving and settling in new countries.
"With the European refugee debate, the focus is always about people entering Europe. But you never know how many people are leaving. Some refugees have moved on," Professor Raymer said.
"It's also unclear how many people are moving around the Asia-Pacific region, including where Australians go when they leave the country."
He said governments need to share data about migration and population flows so they can make better public policy decisions.
Professor James Raymer, Head of the ANU School of Demography, is one of the collaborators on an international paper titled International Migration Under the Microscope, co-authored with colleagues from Europe and the United States, which has been published in Science.
He said at present, countries worked to collect data independently, but often missed out on the number of people who leave their country.
"Migration involves two sets of data - leaving and arriving. A person leaving one area is a person entering another," he said.
"Governments must get better at sharing data. That's the only way we will get better information about migration. The responsibility should be on receiving countries."
The study authors said policymakers and scientists need to prioritise in three areas to better understand migration trends: data communication and modelling, data collection, and training with Masters and PhD programs in migration and population diversity.