The survey includes almost 42,000 Americans at least 15 years old, and was conducted in January. Over 1,500 brands were rated, each receiving about 1,000 scores. At issue is brand strength, not infamous brand recognition. three touchstone criteria are familiarity, quality, and purchase consideration.
Not all included brands are placed in the final list (which can be viewed here). There is not (yet?) a sub-category for streaming music, or Internet radio, that would naturally accommodate Pandora. So it is especially notable that Harris is calling out its performance in the survey.