By the mid-1970s, Sesame Street, according to Davis, had become "an American institution".[102] ETS conducted two "landmark"[103] studies of the show in 1970 and 1971 which demonstrated Sesame Street had a positive educational impact on its viewers.[103] The results of these studies led to the producers securing funding for the show over the next several years,[102] and provided the CTW with additional ways to promote it. By the second season, Sesame Street had become so popular that the design of ETS' experiments to track the show's educational outcomes had to be changed:[104] instead of comparing viewers with a control group of non-viewers, the researchers studied the differences among levels of viewing. They found that children who watched Sesame Street more frequently had a higher comprehension of the material presented.[105]