The US Congress has stepped into the growing row over the Nielsen Media Research ratings system.

Congress has ordered an audit of the under-fire electronic TV ratings system which critics claim undercounts black and Hispanic audiences.

The move further delays Nielsen's plans to introduce people meters to big cities such as New York, Los Angeles and Chicago.

Nielsen, part of Dutch media giant VNU, wants to dump the old diary system still used for measuring local audiences and switch to the electronic system, used for national ratings since 1987.

The ratings specialist contends the electronic system is far more accurate because it can identify the age, race and gender of viewers on a nightly basis.

Previously local demographics were only available quarterly.

The switch-over has been thwarted by the self styled Don't Count on Us Coalition. Another leading critic is Fox Televison, owner of two stations with big minority audiences.

However, if as Nielsen says, the system is not flawed, Fox and other TV stations could lose out financially. Lower ratings mean lower advertising revenues.

Congress insists it is not being partisan, but merely wants an independent inquiry.

It suggests Nielsen should run both systems side by side until the matter is settled.

Data sourced from: The Wall Street Journal Online; additional content by WARC staff