The Walton family, who owns Wal-Mart Stores, is one of the richest families in the US Reuters

The richest 10% of families in the US hold a massive 76% of the country's wealth, it has been revealed. According to statistics released by the government's non-partisan Congressional Budget Office (CBO), income inequality in the country has intensified massively in the past 20 years.

The bottom half of American families owns 1% of the country's total wealth in 2013, according to statistics released on Thursday, 18 August. Debt levels have grown too, with those in the bottom quarter owing $1,000 (£765) in 1989 (the equivalent of $1,910 in 2015) and $13,000 by 2013.

US wealth patterns have changed remarkably in the 24 years between 1989-2013, the CBO found. The top 10% became 54% richer, while those in the middle are just 4% richer. Those in the 25th percentile, meanwhile, are 6% poorer than they were 24 years ago.

Family wealth in the US totalled $67tn – about four times the nation's gross domestic product (GDP) – with a median family (the one at the midpoint of wealth distribution) owning an estimated $81,000 in assets minus debt.

The average wealth of families in the top 10% was around $4m. The average for families on the next rung down (11%-50%) was 316,000, while the third quartile owned just $36,000.

Statisticians found that wealth also congregated around the elderly – families headed by someone who was 65 or older owned on average 3.5 times more than those headed by someone aged 35-49.

Education is important too: the median wealth of families headed by someone with a college degree – $202,000 – was almost four times the median wealth of families headed by someone with a high-school diploma.

The CBO has blamed two developments for the change in wealth distribution: wages for the bottom 50% grew slowly until the 2007-2009 recession, but their pay did not bounce back, causing a steeper decline in wealth by proportion.