I am a songwriter. I write Western Music - mostly in the Country genre.
Every song I have ever written has at least two verses and a chorus. I don't always add a bridge as I recognize that a bridge is not essential.
Sometimes I add a bridge and often it is the same length (usually 8 bars) as the verses. However, I have written several songs where (either through laziness, or because I felt it was enough) I wrote a bride that was only half as long as the verses. For example the verses may be 8 bars long and the chorus may be 8 bars long but I may put in a 4 bar bridge (followed by the final repeat of the 8 bar chorus).
I know that in song writing terminology the "bridge" is often referred to as "the middle eight" thus inferring a preferance for an 8 bar bridge.
My question is, how common is it for songs to have a shorter bridge (say half the length of the verses)? Is there a good reason to try to make the bridge the same length as the verses - or is it perfectly acceptable and/or common to have a bridge that is shorter than the verses?