iTunes allows users to rate songs on a 1 star to 5 star basis, but what if a song is somewhere in the middle of the rating scale, not quite worthy of 4 stars but not a 3 star song either?

For more precise personal ratings, enable the half-star rating option in iTunes:

1. Open Terminal app
2. type:
   defaults write com.apple.iTunes allow-half-stars -bool TRUE
3. Quit and relaunch iTunes for changes to take effect. To give something a half star, click and slide the star rating scale until the 1/2 value shows.

NOTE: removing the half stars moves the song rating to the star below it, so a 3 1/2 star song would turn into a 3 star song, and so on, but the metadata of the songs are still in half-star increments.
So, if you turn the option back on again, the ‘correct’ half-star ratings would show and be intact.