How many of us are really experiencing "bill shock" when we open our monthly cell phone bills? The Federal Communications Commission last week hit back at CTIA after the wireless association accused the FCC of producing a survey that was an "ends-driven invention."

"Rather than focusing on ways to address consumers' concerns, the wireless trade association (CTIA – The Wireless Association) has been hard at work finding unfounded ways to criticize the FCC's data," Joel Gurin and John Horrigan in the FCC's consumer and governmental affairs bureau, wrote in a blog post.

In late May, the FCC released a report that said 30 million Americans have experienced "bill shock," or an unexpected increase in their monthly bills. The report came several weeks after the commission established a task force to look into the issue, and opened up a public comment period on bill shock.

CTIA posted a rebuttal to that report last week, accusing the FCC of polling kids under 18 to buoy its results as well as asking misleading questions in order to establish whether someone had established "bill shock."

Christopher Guttman-McCabe, vice president of regulatory affairs for CTIA, wrote that the FCC's investigation was "interesting" given that complaints per wireless customer have been on the decline. He also said the term "bill shock" was "pretty inflammatory."

One of the things that peaked Guttman-McCabe's interest, he wrote, was the fact that only 902 of the 3,005 respondents said "yes" when asked if they were over 18.

"Let me repeat -- only 30 percent of the respondents said that they were over 18," he wrote. "Despite the survey instructions directing the termination of the interview and recording as ineligible if the respondent was under 18, it appears the survey went on to ask questions and record answers about wireless bills. How many people under the age of 18 actually have ever seen a wireless bill?"

The FCC said Guttman-McCabe's analysis was flawed. The survey questioned people via cell phone and on landlines. For people reached on their cell phones – or 902 people – the surveyor asked, "Are you over 18?" For those reached on landlines – or 2,103 – the surveyor asked "May I please speak to the person age 18 or older in the household who had the most recent birthday?"

"The survey methodology ensured that respondents were 18 years of age or older," Gurin and Horrigan wrote. "The survey also asked respondents to tell us how old they were (standard practice in surveys). All respondents – except for 3 percent who refused to give an age – said they were age 18 or older."

The FCC also took issue with CTIA's conclusion that 13 percent of respondents had experienced "bill shock." The FCC said CTIA used raw data that included results from people who did not have cell phones. Removing that data puts the number at 17 percent of users with bill shock, Gurin and Horrigan wrote.

Guttman-McCabe also had a problem with the vague phrasing in the survey. People were asked if their "cell phone bill ever increased suddenly, from one month to the next, even if [they] did not change the calling or texting plan on [their] phone."

'If I would have been a participant in the survey, I would have said 'yes' too. I have experienced 'sudden increases' in my wireless bills in the past because either my wife or I had been using our devices more. Is it a 'bill shock' though? No," he wrote.

Furthermore, the actual survey did not use the phrase "bill shock," Guttman-McCabe said. "The term is an ends-driven invention by the FCC, not the survey company or the respondents. It was not part of the survey."

The FCC did not address this part of Guttman-McCabe's blog post.

"It's unfortunate that CTIA, which represents one of the country's most innovative and productive industries, has decided that ignoring or distorting the facts is a better strategy than simply addressing wireless customers' concerns," Gurin and Horrigan concluded.

CTIA did not immediately respond to a request for comment on the FCC's post.