As a person receives more of a good, the from each additional unit of the good declines.

Quackwatch.com an expert in medical communications, dr. barrett operates 23 web sites; co-edits consumer health digest (a free weekly electronic newsletter); and has been a peer-review panelist for several top medical journals. he has written thousands of articles and delivered more than 300 talks at colleges, universities, medical schools, and professional meetings. his 52 books include the health robbers: a close look at quackery in america and eight editions of the college textbook consumer health: a guide to intelligent decisions. one book he edited, vitamins and minerals: or harm? , by charles marshall, ph.d., won the american medical writers association award for best book of 1983 for the general public and became a special publication of consumer reports books. his other classics include dubious cancer treatment, published by the florida division of the american cancer society; health schemes, scams, and frauds, published by consumer reports books; the vitamin pushers: how the "health food" industry is selling america a bill of goods, published by prometheus books; and reader's guide to "alternative" health methods, published by the american medical association. from 2012 through 2016, he served as north american co-editor of the journal focus on alternative and complementary therapy (fact). his media appearances have included dateline, the today show, good morning america, abc prime time, donahue, cnn, national public radio, and more than 200 radio and television talk show interviews.