
Up until Summer 2017, complete listings of ratings were not available on the internet for years before 1995, and now this site possesses ratings for several years dating back to 1964. Enjoy the latest entry, as complete 1978-79 and partial 1981-82 data is planned next for sitcom scorecards.
Elsewhere, Barney Miller, Welcome Back Kotter and What's Happening delivered traditional helpings of sitcom delight. Over at CBS, it was time to retool the issue-laden sitcoms as the network cancelled 11 of their 18 helpings. All in the Family was still a top-10 player, yet suffered the loss of Sally Struthers and Rob Reiner, leaving the future of the tart sitcom up in the air. Alice, MASH and One Day at a Time delivered nicely, but renewed Rhoda, The Jeffersons and Good Times all struggled with middling ratings. The upstanding Newhart and issue-icky Maude met less than honorable endings after 6 seasons, and none of the 9 pilots offered this season survived.
Over at NBC, Sanford Arms, a spinoff of uber-successful Sanford and Son, delivered ratings near the drain. After Freddie Prinze, Sr.'s suicide in early 1977, Chico and the Man was never the same and NBC cancelled the series after 4 seasons. Not a single NBC sitcom survived the season, as the network was in its longest depression to date, having started in 1974 and not subsiding until early 1984.
Sources:
1. https://books.google.com/books?id=g5rhcrA0Oi4C&pg=PA91&lpg=PA91&dq=lou+grant+nielsen+ratings&source=bl&ots=VwtexuNYB7&sig=kWbrSQRfsFIBhAXUzREOOo2wQec&hl=en&sa=X&ved=0ahUKEwig_drgyKvWAhXHsVQKHdy7DGcQ6AEIXzAI#v=onepage&q=lou%20grant%20nielsen%20ratings&f=false
2. 2. Chicago Tribune, August 20, 1978 -- https://www.newspapers.com/image/198777664/?terms=1977-78%2BSeason%2BNielsen%2BRatings%2Babc%2Bcbs%2Bnbc
3. http://fbibler.chez.com/tvstats/by_5_yr_period/top_programs_1975-1980.html