Data from questionnaire design can be riddled with problems; for example, if the questions are too detailed or lengthy, the consumer will not think them through properly. If the questions are all closed (e.g., able to be answered with just a ‘yes’ or ‘no’), the specific information being sought may be lost.
Method used for collection may alter the value of the data. For example, if collecting data by telephone, answers may be shortened, unclear, or dependent on non-verbal language to interpret. Collecting data by surveillance method (e.g., observation reporting, sample gathering) may be negatively affected due to limitations of legality, identification, recognition, and so on. Collection by written survey can present problems with handwriting deciphering, paper and ink quality, and the like.
Observational collection approaches can produce problems when interpreting and using the primary data. For example, a covert observational research process (i.e., the researcher observes without announcing his or her purpose) can – depending on market being observed – be corrupted by external influences (e.g., uninvited participants, unscripted behavior and expectations). An overt process (i.e., the researcher announces his or her purpose), on the other hand, affects the useful data since the observed become typically self-conscious and unnatural in responses.