There are an estimated three to four million yacht club members in America.

Evidence

But a publisher might not be aware that Dr. Astra’s book (as she believes) is going to be of keen interest to the estimated three or four million yacht club members across America. — Tilar J Mazzeo, How to Write a Bestseller, 350

Categorization

• XREF: Includes specific market data, emphasizing thorough research for proposals.
• corroborated: 2 independent passages support this claim — Tilar J Mazzeo, How to Write a Bestseller, 350