In answering this question for books it might be instructive to look at what happens in another artistic field, that of the movies. Although there are some major differences (Movies cost a lot more to make and therefore there aren't so many made each year for a start) the comparison might shed a little light.
With rating movies statistically there are a number of methods:
- Box office takings, such as Box Office Mojo
- DVD and Video sales
- Movie audience figures (when broadcast on television or similar)
- Industry awards, such as the Academy Awards or the Baftas
- Ratings from critics, such as Rotten Tomatoes or Metacritic
- Ratings from general users, such as IMDB
- and finally, "Best of" listings voted on by critics or interest groups.
I include the last not because it is really a very good statistical comparison as compared to any of the other methods, but because it is the only one analogous to the sorts of lists being considered in the Worlds Without End rankings.
To get a good statistical ranking for books or movies we need to get a comprehensive set of data that covers all (or most) of the entries, and which applies the same rankings to each. None of the rankings for Movies which I have listed really does that, but some do better than others in some ways at least. For example, ticket and unit sales cover all movies, though they have the problem that the number of people going to movies, and the price they pay per ticket, have increased over time so that the ranking metric isn't the same for all movies. It also has the disadvantage that ticket sales are not necessarily related to how good a movie is. Industry awards can probably be assumed to cover all movies released in a given year and therefore cover the whole population, but have the problem that the award givers may not cover all entries equally, and may be subject to bias. Critical judgement, whether from professional critics or members of the public, also have the problem of coverage - I personally cannot expect to be able to see every movie made, and the ones I do see will be affected by by things like advertising budgets which are not necessarily related to how good the movie actually is.
With books we do have some similar data sets. Figures for number of books printed, or sales on the likes of Amazon can be compiled, though these have the same problem of not being related to quality. I don't know of any compilation sites for professional book critics (anybody?), but there are sites such as Goodreads where members of the public can give their subjective rankings. Industry awards also exist, such as the Hugo or Nebula awards, but these have the disadvantage of being subject to politics (*cough* Puppies vs SJW anyone?). Finally, there are "Best of" lists, such as the ones cited by Worlds Without End.
Books have a problem compared to movies in that far more books get published than movies get made. While a good critic can expect to see all the movies that come out in a year (at least all those released theatrically), reading every book that is published is impossible. This eats into the quality of critical rankings out there, or even into Industry awards. Any "Best of the Year" list can't really hope to be definitive, because a book - especially a ground breaking, iconoclastic new classic - will take time to find a wide audience and be widely recognised.
For my money, I think the likes of Goodreads are probably the best bet as an objective, comprehensive and timely statistical source for rankings of books.