PS4 and Xbox One digital purchases account for up to 25 per cent of total game sales and NPD's monthly reports have become muddied because of it, according to Cowen and Company analyst Doug Creutz.
"[Sales were down] driven by tough comps and the drag from a significant percentage of next-gen software units being sold digitally," Creutz said. "This is not so much a problem for the publishers as it is for brick-and-mortar retail."
"Given the strong shift toward new-gen games that is apparent from recent data, and the fact that digital currently appears to be taking as much as 25 percent share of total new-gen sales depending on the game, we continue to expect total Q4 physical unit sales to be down double-digits year-over-year," Creutz said.
It was reported in July that NPD would begin posting digital sales data this year, but nothing has manifested on that front to this point.
The group only tracks US retail game sales at current, though it has made efforts in the past to obtain and incorporate data from digital sales for its reports.