Are U.S. consumers substituting online streaming services such as Netflix for premium subscription video channels such as HBO, Showtime and Starz? The networks say they have grown their subscriber bases over the last year.

But a study by NPD Group suggests subscriptions to HBO, Showtime, and other premium TV services have declined over the past two years, as Netflix and other subscription video-on-demand (SVOD) services have gained in popularity.

Likewise,  a recent TV Dailies poll conducted by Ipsos MediaCT surveying prime-time viewers’ subscription service behavior suggests that 64 percent of prime-time viewers aged 18 to 49 are what the study calls “Cord Lovers.”

Those are customers who maintained or added to their cable or satellite services in the past six months.

About 27 percent of viewers 18 to 49 are “Cord Shavers”  who had cut back on the level of services in the past six months, while two percent of polled consumers  had cancelled completely.

About seven percent of those who participated in the survey had not had a cable or satellite subscription at all in the past six months. That suggests the “Cord Avoider” population is less than seven percent (some of those with no subscription in the last six months will do so in the future, in all likelihood).

The study also suggests that people who cancel their subscription TV services do so because they are switching to over the top video services. In fact, it is most likely consumers cutting back on subscription television service also are cutting back on other spending and are not adopting over the top streaming services.

Results from the study indicate that those who have cut back on the level of TV subscription services in the past six months were also the most likely group to have cut back on paid online streaming service within the last six months.

That findings broadly suggest people who enjoy television are the most likely to buy all of the available TV services. Those who enjoy television least are most likely not to buy any of the available services.

On the other hand, some also suggest that users are substituting Netflix and other streaming services for premium channels, something the premium channels themselves contest.

According to NPD Group (News - Alert), premium channel subscriptions declined six percent over the last two years, while households subscribing to Netflix and other streaming services grew about four percentage points.

But Showtime says it has added one million subscribers a year in six of the last seven years. HBO says it added 1.9 million subscribers in 2012 and it expects a similar result in 2013.

Starz claims it has added 1.2 million subscribers in the last 12 months, as well.

The point is that it is not precisely clear what is happening in some parts of the subscription video business. Nobody seems to question a slight decline in the total subscription video market (cable TV, satellite and telco TV).