Senator Eliot Shapleigh - El Paso, Texas

Farmers Branch City Councilman Tim O'Hare

Both sides of the debate about illegal immigration repeatedly make assertions that are not based in fact.

Opponents say one-third of prison inmates are illegal immigrants, but state and federal officials say there's no such statistic.

Advocates say illegal immigrants from Mexico come to the United States because they're destitute. But numbers show that they are not that country's poorest and that most of them had jobs before coming to the United States.

Government and private groups believe that more than half of illegal immigrants come from Mexico.

Here's a closer look.

Who's in jail?

Anti-illegal immigration lawmakers and activists have repeatedly said that one-third of prison inmates are in the country illegally.

In September, Dan Patrick, a conservative radio talk show host based in Houston, said 'close to a third' of state inmates are illegal immigrants. Patrick was later elected to the state Senate, where he recently filed a bill that would 'make it illegal to be illegal in Texas' by making undocumented immigrants guilty of criminal trespass.

In January, Farmers Branch City Councilman Tim O'Hare said he 'read it in more places than I can remember' that 29 percent of federal prison inmates are illegal immigrants.

O'Hare is the driving force behind Farmers Branch's anti-illegal-immigration measures that include a ban on renting apartments to some illegal immigrants and making English the city's official language.

Tracy Billingsley, a spokeswoman for the federal Bureau of Prisons, said 30 percent of federal prison inmates are citizens of another country, but it is not known how many of them are here illegally.

'We don't have data when it comes to illegal immigrants,' she said.

State officials do not have that data either, said Jason Clark, spokesman for the Texas Department of Criminal Justice.

Numbers he supplied show that 7 percent of Texas prison inmates claim citizenship in another country. Less than 5 percent have 'detainers' on them from Immigration and Customs Enforcement. This means that they will be turned over to ICE for suspected immigration offenses when they finish serving their state prison sentences.

ICE spokesman Carl Rusnok said his agency does not know how many federal prisoners have ICE detainers. He was skeptical of the claim that one-third of prisoners are illegal immigrants.

'Whatever stats you're hearing is based on something that isn't factual,' he said.

In an interview Wednesday, Court Koenning, Patrick's chief of staff, said the Houston Republican may have 'misspoke' but was referring to information that county sheriffs gave him.

Who's hungry?

On the other side of the debate, illegal immigrants and the people who advocate for them frequently say that the immigrants come to the United States because they need to feed their families.

In an interview with the Star-Telegram in October, Sally Diaz, president of the League of United Latin American Citizens Council 4353 in Arlington, said cities should not crack down on illegal immigrants but instead help them become legal residents if 'it's a hardworking person that just wants to work and feed his family.'

Salvador Parada, an activist and opponent of O'Hare, repeated this assertion in a interview with the Star-Telegram in January.

'If you're put in a situation where you have to break the law to feed your children ... obviously you're going to have to do something,' he said.

In April 2006, activist and illegal immigrant Jose Luis Flores told the Star-Telegram, 'If I don't use a false Social Security number, I'll die of hunger.'

But numbers suggest that illegal immigrants are not that desperate. Most illegal immigrants come from Mexico, which has the highest per capita income in Latin America, according to the World Bank.

Illegal immigrants are not fleeing Mexico for lack of food; they're not even fleeing for lack of jobs.

Only 5 percent of illegal Mexican immigrants in the United States for two years or less were unemployed while still in Mexico, according to a survey of more than 4,800 illegal Mexican immigrants conducted by the Pew Hispanic Center in 2004.

'The big draw is higher incomes, not destitution,' said Gordon Hanson, an economist at the University of California, San Diego and a research associate at the National Bureau of Economic Research. 'It's not the destitute that account for the bulk of immigrants coming over the border. ... It's too expensive for them [to cross], so the bulk of your immigrants are from the middle of Mexico's labor force in terms of their skills and earnings and so forth.'

He said most Mexican immigrants are not driven to the United States by intense poverty but by higher wages.

Hanson said Mexicans with about six years of education can make about $8.20 an hour in the U.S., four and a half times what they can earn in Mexico.

In an interview Wednesday, Parada acknowledged that it's an exaggeration 'to some extent' to say illegal immigrants must come here to feed their families. But he said the poor conditions they're fleeing are real.

'From talking to people [I learned that] they would have been in worse conditions in Mexico,' he said. 'That's one of the reasons they came to the United States.'