Nielsen’s research into these newly TV-less households indicates that they generally have incomes under $20,000. “They are people at the bottom of the economic spectrum for whom, if the TV breaks, if the antenna blows off the roof, they have to think long and hard about what to do,” Ms. McDonough said. Most of these households do not have Internet access either. Many live in rural areas.

The transition to digital broadcasting from analog in 2009 aggravated the hardship for some of these households. Some could not afford to upgrade, Nielsen surmised, though the government tried to provide subsidies in those situations.

And some in rural areas could not receive digital signals as effectively as analog signals for technical reasons. In those cases, “if you’re an affluent household — or most middle-class households — you’re going to get a satellite dish. If you’re a struggling household, likely you’re not going to be able to afford that option,” Ms. McDonough said.

Then there are the tech-savvy Americans who once lived in a household with a television, but no longer do. These are either cord-cutters — a term that refers to people who stop paying for cable television — or people who never signed on for cable. Ms. McDonough suggested that these were younger Americans who were moving into new residences and deciding not to buy a TV for themselves, especially if they “don’t have the financial means to get one immediately.”

Nielsen has not yet assessed what proportion of the decline can be attributed to this behavior. But the decline in the percentage of homes with sets is sure to kick off another round of speculation about cord-cutting.

Sensitive to its clients’ concerns, Nielsen explains the trend this way in the report: “While Nielsen data demonstrates that consumers are viewing more video content across all platforms — rather than replacing one medium with another — a small subset of younger, urban consumers seem to be going without paid TV subscriptions for the time being. The long-term effects of this are still unclear, as it is undetermined if this is also an economic issue that will see these individuals entering the TV marketplace once they have the means, or the beginning of a larger shift to online viewing.”