This excerpt taken from the SIRI 10-K filed Mar 16, 2005.
Average monthly revenue per subscriber, or ARPU. Set forth below is a table showing ARPU and our average monthly revenue per Hertz subscriber:
Lower ARPU for the year ended December 31, 2003 as compared with the year ended December 31, 2002 was a result of promotional activity. Higher reported ARPU was primarily a result of the effects of mail-in rebates. Since we had no history of estimated take-rates for mail-in rebates, we were required to record the effects of rebates for 100% of eligible activations in 2002.