Qpsk decreases the bandwidth

         I learnt that bandwidth is the bit rate. But when I was learning Qpsk I came across this sentence
"For a given bit rate the transmission bandwidth required for Qpsk is half as that of Psk."

I know that in Qpsk a symbol contains two bits and the duration of the symbol is twice that of the PSK but I couldn't quite understand the above sentence.

Any help "for dummies" would be appreciated.

Thanks in advance.