Effective resolution is superior compared to peak-to-peak resolution when comparing ADCs from different companies. An application note from Analog Devices. Link here (PDF)
The low bandwidth, high resolution ADCs have a resolution of 16 bits or 24 bits. However, the effective number of bits of a device is limited by noise. This varies depending on the output word rate and the gain setting used. This parameter is specified by some companies as effective resolution. Analog Devices specifies peak-to-peak resolution, which is the number of flicker-free bits and is calculated differently from effective resolution. This application note distinguishes between peak-to-peak resolution and effective resolution.