How effective were Muckrakers in uncovering social evils in the United States in the early 1900s?

[Jody]

Obviously they were good at it, it was their job, it's what they did for a living and for fun.

They were part of the Social Justice movement of the Progressive Era, they had to be successful. Their constant exposure of wrongdoing by officals in public life led to investigations and later on to reforms of Corporate America, Wall Street, and the government.

Ida Tarbell wrote on Standard Oil's (John D. Rockefeller) monopolization of the gas & oil industry after it fell, exposing manipulation of trusts .

McClure's Magazine published many early muckraker articles. Wiki has a pic of the front cover of a Jan 1901 edition. "Cosmopolitan, The Independent, and Munsey's was also in circulation and read avidly by the growing middle class."