I believe that vibrato is way overused by amateur singers, and is often "forced". Singers hear vibrato on recordings and attempt to mimic it by waving pitches up and down. Vibrato sounds and feels best when it occurs naturally, as the voice rings like a perfectly tuned string. Although I don't know much about vocal technique or vibrato production, David's chapter on vibrato confirms these suspicions for me. I am going to talk with my colleagues and further learn some ways to address the vibrato issue as a teacher - are there ways to discourage unnatural vibrato in the classroom or should the topic be avoided entirely?