Ed Case‘s U.S. Senate campaign released poll results today Tuesday (May 22) that show him to be in a virtual tie with opponent Mazie Hirono.

The interactive-voice-response survey of 667 likely Democratic primary voters over May 15-16 shows Case leading Hirono 46-45 percent with 9 percent undecided.

The poll results are very similar to a Civil Beat poll conducted in January, but it is difficult to assess the validity of the Case poll because it’s unclear exactly what questions voters were asked. The survey was conducted by Boston-based Public Strategy Group.

Case called the poll “encouraging” and said it showed he had momentum and broader appeal than Hirono.

Update: Carolyn Tanaka, deputy campaign manager for communications, Mazie for Hawaii, issued this statement regarding the poll:

It is difficult to comment on a poll that seems to have little meat and information about how it was conducted and therefore doesn’t meet any level of transparency.

Update: Democratic Senatorial Campaign Committee Executive Director Guy Cecil had this to say regarding Case’s poll:

This is only the most recent example of Ed Case releasing highly questionable polling results that don’t line up with any public or private polling. Despite these results (from Case’s third pollster this cycle), everything I have seen suggests that Hawaii voters are strongly supporting Mazie Hirono by double digits in the primary and that she has the strongest chances of winning the general election.

Ed Hasegawa, Lloyd Nekoba and Audrey Case at Ed Case’s headquarters.