If the methodology isn't published the poll is probably garbage. Additionally you have already identified a major weakness in the sample. But haters are gonna hate and even look for any opportunities to do so.
Strong Dem 19
Not very strong Dem 10
Ind Lean dem 9
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So that is 29 Dem, 38 with leaners
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Strict Ind 19
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Ind lean GOP 12
Not very strong Repub 9
Strong Repub 11
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So that's 20 GOP, 31 with leaners
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Other 11
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Other? What the heck is other? People too stupid to have an opinion?
Now, lets look at the March Gallup numbers:
http://www.gallup.com/poll/15370/party-affiliation.aspx 2011 Mar 3-6
GOP 29
Ind 39
Dem 29
GOP/lean 45
Dem/lean 43
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So according to Gallup, Dems and GOP are pretty even. Yet this poll has Dems up 8-9 points over pubbies, plus there is that mysterious 'other' column where all kinds of crap can be buried. So there is easily a possible 15 point bias in this poll, which means -28 could actually be closer to even with realistic samples and registered voters.
This is a pure garbage poll, in other words.