The manager of a shopping center recently conducted a survey to provide information on the types of stores that should be sought for the center's new wing, which was under construction. The questionnaires were distributed by placing them on tables near the entrances to the centre. A large sign above each table said: "Help Us Plan the New Wing." Deposit boxes for completed questionnaires were provided at each table the tables were left up for a two-week period. What types of errors are likely to be present in the study? What changes, if any, would you suggest?