Answer:
The online survey has large biases concerning representativeness. Regarding the behavioural characteristics of consumers, the face-to-face data delivers the best results, followed by the telephone interviews and finally the online survey.
Face-to-face surveys still deliver the most representative results. Telephone surveys may provide a good alternative, but we would advise use of a larger sample. The online survey needs to be corrected, one should relinquish representativeness.