Cooperative systems are being widely investigated and error probability expressions for various network configurations have been obtained. Even though analytical models are accurate, they often lack tractability and do not shed much light on the interplay between channel conditions, network parameters and transceiver characteristics. This paper exploits a recently introduced technique, which uses signal-to-noise ratios to characterise the modulation and coding scheme of transceivers for Rayleigh fading channels. Based on this technique, which allows decoupling of error probability analysis and radio specifications, we derive conditions on the adopted transmission scheme to ensure that cooperation improves the outage probability of each user in decode-and-forward networks with statistically similar or dissimilar uplink channels.