Final answer:
Robocalls have had the most adverse impact on consumers for marketing research via phone, leading to low response rates, potential errors, and legality issues. Privacy concerns also contribute to reduced participation and possible sampling biases.
Step-by-step explanation:
Among the choices provided, robocalls have most negatively impacted consumers when it comes to businesses wanting to conduct marketing research over the phone. Robocalls are automated calls where a pre-recorded voice conducts the survey without a live interviewer. This has led to a host of problems including low response rates, the potential for errors in responding, and legal challenges as the Telephone Consumer Protection Act made automated calls to cell phones illegal. Additionally, the fact that many individuals solely use cell phones and are increasingly employing call blocking features further decreases the efficacy of robocalls for telephone surveys.
Privacy concerns are also a significant issue. As phone users have become more concerned with their privacy, they are less willing to participate in such surveys, leading to potential sample biases that can affect the accuracy of poll results. Moreover, methods like random-digit-dialing, while including unlisted and cellular numbers, cannot always assure accurate demographic representation due to changes in phone usage patterns and preferences.