Actually... that report leans very heavily on the Survey of Consumer Finances [0], which is absolutely a sampling (latest iteration was 6500 families out of the 120 million households in the US).
Per page 3 of the report: "We use the Federal Reserve Board’s Survey of Consumer Finances (SCF), which covers family heads born throughout the twentieth century, to determine whether the economic and financial benefits of obtaining a postsecondary degree have changed over time."
