These are books paired by author. At this stage, I have only read the first book in each pair. Generally I chose one of the author's most highly-rated books on Goodreads for '2nd place.' I also commonly used the next unread book in a series.
Note: The second book of each pair may occasionally seem quite esoteric. This could be because the author has published very few works or only a small number are widely read (see below). Alternatively I could have already read their most popular works.
Until I compiled this challenge I never realised how many authors are basically one-hit wonders. For example, regarding Winifred Watson, "Miss Pettigrew Lives for a Day" has 14,000+ ratings on Goodreads, whereas her other 3 listed books have ratings of only 4, 3 & 2. So I omitted her from the list.
