Another public poll, this one from Public Policy Polling, shows a tight race for Senate in Massachusetts. But more interesting is what the Democratic firm does not discuss in its very brief memo about the June 25 special election.

The survey showed Rep. Edward J. Markey, D-Mass., leading Republican Gabriel Gomez by 7 points, 48 percent to 41 percent. That marked a slight increase from Markey’s 4-point margin in a PPP poll two weeks earlier. It’s a single digit margin that is similar to most other post-primary polls.

Even when the PPP numbers seem reasonable, as these do, the firm’s memos accompanying its data usually have a clear Democratic tilt, highlighting results that seem to enhance the Democrat’s standing in the race. This memo is particularly misleading.

While the PPP memo refers to ballot tests among Democratic and Republican voters and notes poll numbers that convey a sense of momentum for Markey, it never mentions independents, a key voter group in the state. Yet the cross-tabs released by PPP show Gomez leading among independents 56 percent to 33 percent, a 23-point margin that is considerably larger than Gomez’s own recent OnMessage, Inc. poll, which showed the Republican leading among independents 50 percent to 36 percent.

The OnMessage, Inc. survey showed Markey leading Gomez overall by just 3 points, 46 percent to 43 percent.

Gomez will have to do better among independents than former Sen. Scott P. Brown did because the GOP nominee will not do as well among Democrats.

The PPP results confirm what we have been seeing since the primary — a competitive special election in a state that normally is a slam dunk for Democratic candidates in federal contests.

It isn’t surprising that Democrats would “come home” after the primary and after Markey and the state media began to focus on Gomez, a former Navy SEAL who has never held office.

But the fact that the Republican continues to do well with independents — a large voting group that Brown won comfortably during his 2010 special election victory — suggests that the Massachusetts special election contest will merit watching in the weeks ahead.

In PPP’s most recent survey, which was paid for by the League of Conservation Voters, the firm polled 880 likely voters from May 13 to 15.