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  1. The Causes of Survey Mode Differences and Their Implications for Survey Design by Don A. Dillman Thomas S. Foley Distinguished Professor of Government & Public Policy and Deputy Director of the Social & Economic Sciences Research Center Washington State University Pullman, Washington 99164-4014 http://survey.sesrc.wsu.edu/dillman/ A Presentation made to The Gallup Organisation Europe in Brussels, Belgium, February 24, 2003 ©Don A. Dillman

  2. Why Discuss Surveys That Collect Data Using More Than One Mode (e.g., face-to-face plus telephone, or the Internet)? • High costs and response rate concerns have forced many survey sponsors to reconsider traditional face-to-face (and telephone) one-mode surveys. • We now have at least five survey modes capable of collecting quality data. • Combining new and old modes may improve response rates and lower costs. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  3. Objective To answer three questions: • Do different survey modes produce different answers to survey questions? • What are the reasons for those differences? • What might be done to reduce differences across modes? ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  4. More Survey Modes are Available For Use Than in the Past • Telephone • Face-to-Face Interviews • Touchtone Data Entry or Interactive Voice Response (IVR) • The Internet • Mail (See Dillman, D. A. 2002 “Navigating the Rapids of Change.” Public Opinion Quarterly p. 66(3): 473-494.) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  5. Mode Differences That Affect Respondent Answers Conclusion: Mail and telephone are most different; others may be varied. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  6. Past Research on Mode Differences • Many differences have been observed in past research, including: Social desirability Acquiescence Primacy/Recency Extremeness on scales • Our research knowledge about some modes is better than for others. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  7. Interview Presence May Have a Normative Influence: Social Desirability How would you rate your health? 60 50 50 50 43 Mail 42 38 Telephone 40 30 Face-to-face Percent 30 18 20 10 10 10 2 2 1 0 Excellent Good Fair Poor (Hochstim, 1967) Respondents more likely to give culturally acceptable answer on telephone or in-person. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  8. Interview Presence May Have a Normative Influence: Social Desirability Results from self-administered questionnaire followed by face-to-face re-interview one month later (Biemer, 1997). Percent ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  9. Interview Presence May Have a Normative Influence: Social Desirability How often do you drive a car after drinking alcoholic beverages? Percent Frequently Occasionally Seldom Never Don’t Know (2 = 14.8 p < .001) Respondents are more likely to give culturally acceptable answer. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  10. An Effect of Interviewer Presence: Acquiescence, the Tendency to Agree Percent of respondents who agree with each of 9 opinions on how to encourage seat belt use Percent (Dillman & Tarnai, 1991, pp. 73-93) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  11. An Effect of Locus of Control: Primacy vs. Recency Student Survey: To what extent do students benefit from cheating? Percent (2 6.9df = 3 p  .07) Primacy in mail (choosing first answer categories) vs. recency in telephone (choosing last categories). ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  12. Effects of Locus of Control: Primacy vs. Recency Student Survey: To what extent do students benefit from cheating? Order Left to Right Order Reversed Percent (2 6.9df = 3 p  .07) (2 6.49df = 3 p  .10) Primacy in mail (choosing first answer categories) vs. recency in telephone (choosing last categories) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  13. 59 Primacy/Recency Comparisons from 12 Studies* *Dillman et al., 1995. Rural Sociology 60(4): 674-687 Results from these experiments show much inconsistency. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  14. 23 Explicit Mail/Telephone Comparisons from Three Studies* *Dillman et al., 1995. Rural Sociology 60(4): 674-687 Results from the direct comparisons show much inconsistency. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  15. Primacy vs. Recency: Conclusions Considerable literature has suggested that primacy in mail and recency in telephone may exist because of cognitive processing patterns. There are clear cases of effects in the literature, as well as exceptions. I suspect that the issue is much more complicated than cognitive word processing; social desirability and visual effects may have simultaneous and competing influences. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  16. An Effect of Aural Communication: Greater Extremeness on Four-Point Scales in General Public Survey Percent choosing “not a problem” (vs. small, moderate, or serious) Percent Police Protection Quality of Schools Low-income Housing Resident Concerns Rec/Park Facilities Medical Services Streets/Roads/ Sidewalks Street Lighting Houses/Apts. to Rent Mean for 9 Questions: Telephone, 47.1 Mail, 31.9 Difference, 15.2 (Dillman & Mason, 1984) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  17. An Effect of Aural Communication: Greater Extremeness on Four-Point Scales in Student Survey Issue is NOT a problem. Percent (Tarnai & Dillman, 1986) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  18. Can Extremeness Be Reduced By Asking Respondents to View Show Cards When Responding? Perhaps. Student experiment with three treatment groups: 1. Visual: Self-administration 2. Aural: Telephone 3. Aural plus Visual: Telephone interview conducted with respondent while viewing self-administered version. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  19. Effects on Extremeness of Three Kinds of Administration Percent who chose “not a problem” (vs. small, moderate, serious). Percent Combined administration (visual + aural) may moderate extremeness. (Tarnai & Dillman, 1990) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  20. A Study of Aural vs. Visual Communication: Telephone, IVR, Mail, and Web A Gallup study compared telephone and IVR (aural modes) and mail and web (visual modes). Questions were comparable across modes. (Dillman, Tortora, Phelps, Swift, Kohrell and Berck, 2000) Q2. Overall, how satisfied are you with your long distance company?  1 Not at all satisfied  2  3  4  5 Extremely satisfied Q3. Considering what you get and what you pay for it, how would you rate the overall value of your long distance company’s products and services?  1 Terrible  2  3  4  5 Outstanding ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  21. Effects of Aural vs. Visual Communication in Gallup Experiment. Percent choosing positive labeled end-point Telephone IVR 60 Mail 50 50 43 Web Percent 39 39 40 36 33 29 29 30 27 26 21 21 22 21 19 20 18 18 16 11 9 10 0 T I M W T I M W T I M W T I M W T I M W Q2 Q3 Q4 Q5 Q6 ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  22. Summary of Major Observed Differences Among Survey Modes Social Desirability Bias: Telephone and face-to-face (cultural influence). Acquiescence Bias: Tendency to agree on telephone and face-to-face (cultural influence). Primacy Bias: Mail and web (cognitive influence). Recency Bias: Telephone (cognitive influence). Extremeness on Scale Bias: Telephone and face-to-face (aural vs. visual communication). ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  23. Construction as a Source of Mode Differences Survey designers tend to construct items differently for different survey modes. Telephone Favors:  Shorter scales.  Fewer words (e.g., numbers with endpoint labels).  Dividing questions into multiple steps.  Accepting “no opinion/don’t know/refuse” only if volunteered.  Complex branching formats using simpler questions.  Open-ended formats with follow-up probes.  Yes/No questions instead of check-all-that-apply formats.  Keeping questionnaires short. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  24. Construction as a Source of Mode Differences (continued) Face-to-Face Favors:  Use of show cards for complex/lengthy questions and to maintain respondent interest.  Unlimited scale length or format (with show cards).  Longer questionnaires are feasible. IVR Favors:  Even briefer wording formats than telephone.  Even shorter scales than telephone.  Even shorter questionnaires than telephone. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  25. Construction as a Source of Mode Differences (continued) Mail Favors:  Avoiding branching formats.  Use of longer scales with words, numbers, symbols, and graphical information to aid comprehension.  Avoiding open-ended formats or asking them as a sequence of shorter questions.  Check-all-that-apply instead of Yes/No questions. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  26. Construction as a Source of Mode Differences (continued) Internet Favors:  Check-all-that-apply formats (html box feature).  Use of longer scales with words, numbers, symbols, and graphical information to aid comprehension.  Addition of audio, video, color, and other dynamic variations.  Keeping questionnaires short. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  27. Unintentional Construction Effect: Open vs. Closed Format Telephone: What is your marital status? (Open-ended, coded by interviewer.) Web: What is your marital status? (Click the category that applies. If you inadvertently click the wrong category, you can correct the error by simply clicking on the correct category.) Single Married Separated Divorced Widowed ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  28. Unintentional Construction Difference: Results from a Telephone (Open-Ended) and Web (Close-Ended) Comparison What is your marital status? Differences are significant and tracked across additional panels. (Tortora, 2001) ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  29. Unintentional Construction Effect: Volunteered Responses on Telephone To what extent do you favor or oppose expansion of NATO? Telephone: Mail: 1 Strongly favor 1 Strongly favor 2 Somewhat favor 2 Somewhat favor 3 Somewhat oppose 3 Somewhat oppose 4 Strongly oppose 4 Strongly oppose 5 NO OPINION 6 DON’T KNOW 7 REFUSE ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  30. Examples of Unintentional Construction Difference: Check-All-That-Apply vs. Response to Each Item • Mail, Web: Please check which of these appliances you have in your home. • Telephone: Which of the following electric appliances do you have in your home? Do you have … (read each item and obtain answer). • Mail/Web: Telephone: • Toaster Toaster Yes No • Broiler oven Broiler oven Yes No • Food blender Food blender Yes No • Meat slicer Meat slicer Yes No (other items) (other items) The threat to response in check-all-that-apply questions is “satisficing” i.e., answering only until the respondent feels s/he has given a satisfactory answer. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  31. Unintentional Construction Difference: Breaking Questions Into Parts on Telephone or IVR Step 1: Are you … Satisfied Dissatisfied Neither Satisfied or Dissatisfied Step 2: If Satisfied – Would that be Completely Satisfied, Mostly Satisfied, or Somewhat Satisfied? If Dissatisfied – Would that be Completely Dissatisfied, Mostly Dissatisfied, or Somewhat Dissatisfied? If Neither – Would you tend towards being Slightly Satisfied, Slightly Dissatisfied, or Completely Neutral? ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  32. Conclusion on Construction Effects One of the most common reasons mode differences appear in surveys is because questions are constructed differently across modes. First step for reducing mode differences is to reduce construction differences. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  33. Differences in Visual Layouts May Also Affect Answers • Increasing evidence exists that written questions are communicated through multiple languages – words, symbols, numbers, and graphics. • Graphics is the conduit through which other languages are communicated and consists of such factors as figure-ground composition, location and spacing, size changes, brightness variations, and changes in similarity and regularity. • See paper to be presented at 2003 American Association for Public Opinion (AAPOR) meetings by Don A. Dillman and Leah Christian, “How Words, Symbols, Numbers, and Graphics Affect Respondent Answers to Self-Administered Surveys: Results from 18 Experiments.” at http://www.sesrc.wsu.edu/dillman/. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  34. Four Examples of How Changes in Visual Layout Changed Respondent Answers Vertical vs. horizontal layout of scales. Change in size of open-end answer space. Check-all-that-apply vs. Yes/No Answer box vs. scalar layout. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  35. Is Response to Ordinal Scale Influenced by Linear vs. Nonlinear Visual Format? (Dillman and Christian,2002) Nonlinear Linear ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  36. Result: Uneven Number (Five) of Categories With Scale Running Horizontally, by Row Mean 2.4 vs. 2.4 Chi square = 10.8, p<.05 *Categories where differences most likely to occur ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  37. Does Amount of Space Influence Answers to Open-ended Questions? Dillman and Christian,2002) Expected answers could exceed allocated space ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  38. Number of Words in Response to Three Questions ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  39. Number of Themes Mentioned in Each Answer ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  40. Does a Change From Check-All-That-Apply to Yes/No Format Influence Choices? (Dillman and Christian, 2002) Form A Form B ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  41. Rationale for Considering Change from Check-All-That-Apply to Yes/No Format • Reduce tendency to satisfice. • Develop same format for self-administered questionnaires that is already used in telephone surveys. • Drawback: respondents may only check the “Yes” choice and leave others blank. Does a blank answer mean “No”? ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  42. Result: Which Yes/No check-all-that-apply formats for Cougar varsity sports considers self to be a fan of? Men Baseball Women Bsktball Men Bsktball Women Cross-C. Men Cross-C. Football Women Golf Men Golf Women Rowing Women Soccer Women Swim. Women Tennis Women Track Men Track Women V-ball Don A. Dillman, SESRC February 2003

  43. Conclusion: Effect of Changing from Check-All-That-Apply to Yes/No Format • With Yes/No format all sports except football received 4 to 14% more mentions. • 11% of respondents checked only Yes answers • The number of blank answers on Yes/No format ranged from 9-13% (excluding football, 3%); People responded as if it were check-all-that-apply, rather than being less likely to choose Y/N. • The Yes/No format appears to reduce satisficing. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  44. Does a Number Box Produce Same Responses as a Five-Point Scale with Labeled Endpoints? (Dillman and Christian, 2002) Labeled Endpoints Number Box ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  45. Result: On a scale of 1 to 5, where 1 means “Very Satisfied” and 5 means “Very Dissatisfied”, how satisfied are you with the classes you are taking this semester? Mean 2.4 vs. 2.8 t=7.7, p<.001 ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  46. Conclusion: Three Tests of Number Box vs. Polar-Point Scale • On all three questions, respondents provided significantly less favorable answers when the number box was used. • May have resulted from some respondents reversing the scales. On the number box version, there were 10% (vs. 1% for polar-point scales) of respondent scratched-out answers to at least one of these, and provided different answers. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  47. Evidence of Confusion Among Number Box Respondents • 74 (14%) of respondents changed 86 answers. • Two-thirds (52) of them made these 59 reversals: changed 4 to 2.…………….. 44 changed 2 to 4.………………. 4 changed 5 to 1……………… 10 changed 1 to 5……………….. 1 • These data suggest that direction of scale was mentally reversed by a significant number of respondents. • Others probably didn’t realize error had been made because correlations of number box answers with 13 other satisfaction items were consistently lower than polar-point scales, (36 comparisons lower vs. 3 higher). ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  48. Additional Conclusions: Number Box vs. Polar-Point Scale • Some respondents may have “expected” more positive answers (e.g., Very Satisfied) to be assigned higher numbers. • Use of graphical and symbolic language to support verbal language eliminates potential confusion. ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  49. How Do We Minimize Mode Differences Across Surveys? Control of Question Formats 1. Keep wording the same (all modes). 2. Keep questions simple (fewer response choices) and use less abstract response choices (e.g., polar-point labeled scales). 3. Avoid using “hidden” response categories (telephone and face-to-face). 4. Keep visual layout the same (mail and web). 5. Do not use check-all-that-apply questions (mail and web). ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003

  50. Additional Suggestions for Minimizing Mode Differences in Mixed-Mode Surveys? 1. Limit a study to similar modes, e.g., telephone and face-to-face, or for another survey situations use only mail and Internet. Be careful about mixing visual with aural communication. 2. Adjust procedures for a particular mode (e.g., don’t use show cards for face-to-face interviews in order to get telephone equivalence). 3. For visual modes (web and mail), maintain the same language composition (words, symbols, numbers, and graphics). ©Don A. Dillman, The Social & Economic Sciences Research Center February 2003