Editor's note: Mark Goodin is president of Aaron-Abrams Field Support Services, a Las Vegas research company. 

The number of people willing to spend time participating in qualitative research is shrinking. Many are even refusing to take calls from recruiters these days. That's why researchers must take steps to keep our respondent pool well-stocked with quality individuals. Following are four ways in which market researchers can protect the respondent pool and help ensure the long-term health of qualitative research:1. Streamline your screening process. Respondents have grown weary of lengthy screening questionnaires. A seemingly endless barrage of questions invites respondent fatigue, and they simply zone out. Respondents who don't give 100 percent of their attention to recruiters may incorrectly qualify for your research. How long should it take to administer a screening questionnaire? Based on our experience, we suggest under 10 minutes.  2. Make it easier for respondents to qualify. Most respondents who fail to pass the screening process tell us that they believe they are actually answering survey questions, but without being compensated. As a result, the next time a recruiter calls, these respondents won't answer because they don't want to "work for free." Long screening questionnaires and numerous failed recruitment attempts sour respondents against market research and shrink the respondent pool.3. Offer adequate incentives. Many researchers offer respondents a "fun and exciting time" in lieu of a proper incentive. If you truly want to offer respondents a fun and exciting time, send them to Magic Mountain or Disneyland. Respondents are acting as consultants for you when they participate in your research, and they therefore deserve suitable compensation. Attractive incentives not only help ensure that your respondent pool will remain well-stocked, but they also raise respondent cooperation rates.4. Choose ...