NEW YORK (CNNMoney.com) – It's not your imagination. The rich are getting richer, but they're welcoming fewer new members into their club than they have in the past few years, according to a survey released Tuesday.

Worldwide, the number of high-net-worth individuals in 2005 grew to 8.7 million people, up 6.5 percent from the year before, according to the annual World Wealth Report by Merrill Lynch and Capgemini. And the amount of wealth they controlled rose 8.5 percent to $33.3 trillion

Merrill Lynch and Capgemini define high-net-worth individuals as those with $1 million in investable assets, excluding the value of their homes and consumer durables.

In the United States - which still houses the largest number of millionaires - the number of high-net-worth individuals grew 6.8 percent to 2.7 million people in 2005. But that represents a slowdown from the 9.9 percent increase in 2004.

Millionaires in North America controlled $10.2 trillion in wealth, up 9.4 percent from $9.3 trillion a year earlier. That the growth in wealth outpaced the growth in the number of high-net-worth individuals suggests an increased concentration of wealth among the few, a pattern also seen on a global basis as well.

Another indicator of wealth concentration is the wealth held by ultra- high-net-worth individuals, defined as those having at least $30 million in investable assets. There are only 85,400 people worldwide in this group, accounting for just 1 percent of the high net worth group, but they control about a third of the high net worth group's wealth.

Between now and 2010, Merrill Lynch and Capgemini forecast that wealth growth rates may continue to slow to an annual average rate of about 6 percent due to four factors:

• A slowing of the economy relative to three years of strong growth;

• Oil prices, which may continue to affect the purse strings of consumers and businesses worldwide;

• A gradual slowing of China's economy, which will have both a regional and global impact;

• A continued tightening of monetary policy by central banks worldwide.

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