HALF of all marriages end in divorce. Or that's what we are led to believe.

Research from social analysts McCrindle Research shows one in three, and not one in two, marriages will end in divorce.

The Australian Bureau of Statistics-based research was carried out to disprove five commonly accepted but incorrect assumptions often heard in daily life.

Other myths were:

SEVEN-YEAR ITCH: The average marriage lasts longer than seven years.

Average separation is 8.8 years and average divorce 12.3 years.

BABY BONUS FERTILITY: Fertility rate of teenage and young mums has not increased with the baby bonus introduction.

BOOMING POPULATION: The world's population of seven billion is not greater than the total number of people who have ever lived.

YOUNG PEOPLE WON'T OUTLIVE THEIR PARENTS: Life expectancy has increased despite an increase in childhood obesity.

Social analyst Mark McCrindle said the myths had become accepted because figures and percentages had given them an element of believability.

"Marriages are actually doing better these days and the divorce rates are declining and have been for more than 30 years," he said.

"Not only is the rate declining but the total number of divorces is declining."

The introduction of the baby bonus incentive in 2002 was predicted to lead to an increase in the number of single and young mums.

However, Mr McCrindle said the birth rate of teenagers had dropped in the past 10 years. "A 32-year-old (woman) is 10 times more likely to be having a baby than a 17-year-old (woman)," he said.

The research also showed while childhood obesity had risen, the mortality rate of children was less than half the 0.4 deaths per 1000 recorded in 1990.

Mother-of-three Alana White, of Tea Tree Gully, said she believed more people were delaying having children until later in life so they could put their career first.

She said there would always be critics of financial-based incentives.

"I personally didn't have kids for the money," she said.