Unfortunately, the source is NOT an article, but just a mere website operated by a marking firm. I'm waiting for the original poster's answer on how reliable source it is because I've never heard of the firm name until today.
Well, just because it's a marketing firm doesn't mean that they aren't using a valid and recognized index. And really it makes sense that a marketing firm would publish this because their business is marketing and they are talking about marketability. In fact, I would expect that they would be more familiar with determining marketability than would a newspaper, as that is their business. There's a lot of data analysis and statistics that goes into marketing.