We present follow-up observations of 97 point sources from the Wilkinson Microwave Anisotropy Probe ( WMAP ) 3-year data , contained within the New Extragalactic WMAP Point Source ( NEWPS ) catalogue between -4 \degr \leq \delta \leq 60 \degr ; the sources form a flux-density-limited sample complete to 1.1Jy ( \approx 5 \sigma ) at 33GHz . Our observations were made at 16GHz using the Arcminute Microkelvin Imager ( AMI ) and at 33GHz with the Very Small Array ( VSA ) . 94 of the sources have reliable , simultaneous – typically a few minutes apart – observations with both telescopes . The spectra between 13.9 and 33.75 GHz are very different from those of bright sources at low frequency : 44 per cent have rising spectra ( \alpha _ { 13.9 } ^ { 33.75 } < 0.0 ) , where S \propto \nu ^ { - \alpha } , and 93 per cent have spectra with \alpha _ { 13.9 } ^ { 33.75 } < 0.5 ; the median spectral index is 0.04 . For the brighter sources , the agreement between VSA and WMAP 33-GHz flux densities averaged over sources is very good . However , for the fainter sources , the VSA tends to measure lower values for the flux densities than WMAP . We suggest that the main cause of this effect is Eddington bias arising from variability .