Our research has shown that approximately half of the people coming into a library are looking for a specific title or author. The other half want to browse what's there and see what happens to take their fancy. This gives a 50-50 split in preferred method of choosing.
Half of the people who are looking for something specific can't find it - either because they are looking in the wrong place or because when they get there the book is already out. These people then make a substitution - usually at random and nearby. If they have come in for John Grisham they will go out with another G or H, it is highly unlikely they will take a T. Although they began as focused choosers, this group have become browsers.
If we add the 50% who start off by browsing to the 25% who end up doing it we reach a staggering conclusion that 75% of the library audience choose by browsing. The numbers will vary a little (test it out with your own survey) but a broad 75/25 holds good as a guideline. Interestingly, the retail sector tells a similar story. The Book Industry Study Group in the USA found that unplanned, impulse purchases accounted for 60% of all books sold.
Libraries are mostly designed to meet the needs of the 25% of people who know what they want and can find it - the A-Z shelves, the categories of fiction, the Dewey system, the catalogue. The measure of library professionalism is often how fast can staff find a particular book if asked for it.
Reader development has drawn attention to the neglected majority. What can you offer the 75% to help them browse more effectively? You don't need to change the whole library, just offer something to make browsing easy.
In 2001The Mind's Eye promotion showed 75/25 is true with non-fiction too. Titles which had languished unasked for on the shelves were borrowed by browsers when put into an attractive face-on display.