Only responses where both the sales and/or purchases sections of the survey had been completed, and where no discrepancies within the data were flagged, were included within the analysis.
Dim ond ymatebion lle’r oedd adrannau gwerthu a/neu brynu’r arolwg wedi’u cwblhau, a lle na nodwyd unrhyw anghysondeb yn y data, a gafodd eu cynnwys yn y dadansoddiad.