On top of that, most REITs are reporting little to no upward movement in rent-to-income ratios. Home Properties, before being taken private by Lone Star Funds, announced earlier this year that its rent-to-income ratio of 16.9% was "well below 2007 through 2013 levels." Equity Residential said in a Q2 earnings call that their rent-to-income ratios remain stable (at 20%) and "will never change." Other REITs—including AIMCO, Camden, Essex, MAA and UDR—also have reported stable numbers.

Beyond rent-to-income ratios, a litany of additional metrics back up the story that affordability in market-rate apartments is grossly overblown. Vacancy rates are at historically low levels while retention rates are at historically high levels, meaning that, despite rent hikes, apartments are full and renters are increasingly choosing to renew their leases. Furthermore, several REITs have reported declines in unpaid rent.

How is this possible given all the noise we're hearing on affordability right now? One prominent economist said recently on CNBC: "We still have an affordability crisis in the United States with rents rising faster than incomes for the fourth consecutive year." Another well-known economist was quoted by several media outlets saying: "From an affordability perspective, rents are crazy right now."

Here's the problem: Economists rely on wage data from public sources and on new-lease rent data from companies that track primarily market-rate apartments. It's apples and oranges. The income data used in these analyses represents the averages for essentially all working US households. But only about 10% of households live in market-rate apartments.

The reality is that market-rate apartment households are not representative of the US averages; they've fared much better economically. The median income for market-rate apartment households nationally is close to $70,000—well above the US average of nearly $54,000 despite skewing younger in age, according to RealPage data pulled directly from property managers. The economic environment apartment executives are seeing is materially healthier than the macroeconomic climate you hear about in the news.

"On a year-over-year basis, average income in our portfolio of our residents is up about 6.5%," AvalonBay COO Sean J. Breslin said on his company's Q3 earnings call. "So if you're seeing that kind of income growth out of our markets, we should be able to realize above-trend rental rate growth on a sustainable basis."

Another REIT executive, Essex Property Trust CEO Michael Schall, said on his company's Q2 earnings call that Essex is "adding some very high-income renters, so not only do we have great job growth, but we have … high-paying jobs."

In fairness, we should point out that rent-to-income ratios apply only to new residents, who provide their income when applying for a lease. Income data isn't generally collected upon lease renewal. However, reported rent growth figures are also only for new residents. Operators typically charge somewhat less for residents renewing their leases.

Additionally, it's important to remember that rent growth patterns are cyclical. Inflation-adjusted rents actually trended downward between 2002 and 2009. Rents have outpaced inflation since 2010, but didn't return to 2002 indexed levels until the second half of 2014.

This isn't to say there's no affordability problem. There is certainly a very big problem. But the fears and sympathies are misdirected. The real crisis is the nation's severe shortage of designated affordable housing units serving a growing number of low-income households.

These are renters who couldn't afford market-rate apartments even prior to recent rent hikes. The Joint Center for Housing Studies at Harvard University, in its 2015 report, estimated that for every 100 very low-income renters in the US, there are only 58 affordable units available.

Doug Bibby, president of the National Multifamily Housing Council, has talked exhaustively of late about this critical issue, trying to steer policymakers and media to delineate between two largely unrelated sectors—market-rate apartments and income-restricted housing. One huge challenge is that affordable housing development isn't economically feasible without public subsidies, but government housing programs are overwhelmingly geared toward encouraging homeownership, not renting.

This isn't to say no one is moving out of market-rate apartments due to higher rents. Media anecdotes are aplenty, and every apartment operator will tell you it happens. But bear this is mind: A middle-income renter priced out of a market-rate unit can likely find a new apartment in another spot—just perhaps not in the preferred neighborhood. A low-income household doesn't have even that option.

Jay Parsons is director of analytics and forecasts at MPF Research, a division of RealPage Inc. He may be contacted at [email protected]. The views expressed here are the author's own.