Source: AC Nielsen Media Research
TNA iMPACT on Spike TV averaged a 1.2 rating for the period from Jan 5-May 29 (21 weeks)
ECW on Sci-Fi averaged a 1.2 rating for the same period
So based on ratings one might think ECW is leading TNA iMPACT in season to date average.
The rating is the % of US Households watching the show on the cable network.
However, Spike TV is available in approximately 97 million Households while Sci Fi is available in only 93 million households, but ratings are based on each cable network's household audience reach, which is different from broadcast which is based on all available US households.
For example, CBS is available in approximately 113 million households.
So TNA's 1.219 rating = 1,182,430 Households on Spike TV
And ECW's 1.242 rating = 1,155,060 Households on Sci-Fi