On a CCTV 9 show shot in Shanghai, a couple of people who were certainly speaking Putonghua have made comparisons and if I heard right they were pronouncing 比较 as "biao." Am I wrong? Is that a common contraction? Is it typical of Shanghai?
When someone is speaking fast, or speaking casually,
I don't know in which area this usually happens. Native Chinese can "correct" this pronunciation variation automatically and may not even notice this.
This kind of weakening of sounds happens in every language. In Chinese, it may happen in a syllable or in a word, or even among a phrase. Usually, this kind of weakened syllables are auxiliary words which help construct the sentence.
There is coarticulation which means that adjacent syllables would affect the pronunciation of each other, and they all sound differently from when they are pronounced alone.
An interesting result of this is that if you cut out a single syllable from a spontaneous sentence, there is high probability that even natives cannot figure out what it is, although they would have no problem understanding the full sentence.
比较 pronounces 'bǐ jiào' in Putonghua not 'biao (表)' , I'm not from Shanghai I don't know if it's the same in their dialect， ‘biao' sounds like they were speaking Taiwan dialect or they just intended to speak in a nauseating way.