Unfortunately, such data cannot be collected on many organisms, including Daphnia, since it is not possible to track them in the environment.
The catch is that the money cannot be collected any sooner than age 45.
After three years, the money cannot be collected without an employee's consent.
"There's never been a guideline for scholars about what can be collected and what cannot be collected," Ms. Gao said.
Because of time, cost, and other considerations, data often cannot be collected from every element of the population.
"After accounts have matured, you start to get a spike in charge-offs," she said, using the industry term for accounts that cannot be collected.
It is broken down by type of tax, customer group and customer behaviours, including tax evasion and avoidance, customer error, the hidden economy, criminal attacks and where tax cannot be collected because of insolvency.
While in past years, most corrections involved recognition of revenue, reserves -- money set aside to cover anticipated costs for restructuring, liability, debts that cannot be collected or other expenses -- were the most common issue in 2003.
These taxes cannot be collected again until Congress passes another extension of the legislation that finances the F.A.A. Before Friday, the extension had been stalled repeatedly, and its budget temporarily extended 18 times over the last four years.
