The metric that tracks the would-be success rate is known as the Sample Performance Indicator (SPI). And it was at its zenith since May 2004 a week ago. In that the National People Meter sample stood at 12,300 homes; it is now at 20,000.
Nielsen said the SPI results are due to investments made in "meter technology, statistical and methodological research and field operations."
"In addition, our measurement now features 100% digital measurement and we are faced with an increasingly complex home television environment, with more total and more sophisticated televisions per home," Nielsen said in a client memo.