National Academies Press: OpenBook

A Strategic Approach to Transforming Traffic Safety Culture to Reduce Deaths and Injuries (2018)

Chapter: Appendix C Samples Required in Representative Surveys

« Previous: Appendix B Guidelines for Design of Surveys (Task 2 Report)
Page 124
Suggested Citation:"Appendix C Samples Required in Representative Surveys." National Academies of Sciences, Engineering, and Medicine. 2018. A Strategic Approach to Transforming Traffic Safety Culture to Reduce Deaths and Injuries. Washington, DC: The National Academies Press. doi: 10.17226/25286.
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Page 124

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C-1 Appendix C – Samples Required in Representative Surveys The following table summarizes the number of samples required (e.g., completed surveys) assuming random selection to achieve a certain confidence level for a given population size. To use the table, identify the overall population size on the left-hand column, and then select the column with the desired confidence interval to determine the required number of samples. For example, for a population of 500 and a desired confidence interval of ±5%, 217 completed surveys are required assuming random selection. Table 8. Number of Completed Surveys Required Assuming Random Selection Population Size Confidence Interval (at 95% confidence level) ±10% ±7% ±5% ±3% 25 20 22 24 24 50 33 40 44 48 75 42 54 63 70 100 49 66 80 92 150 59 85 108 132 200 65 99 132 169 300 73 119 169 234 500 81 141 217 341 1,000 88 164 278 516 1,500 90 173 306 624 2,000 92 179 322 696 3,000 93 184 341 787 5,000 94 189 357 880 10,000 95 192 370 964 20,000 96 194 377 1013 40,000 96 195 381 1039 80,000 96 196 382 1053 160,000 96 196 383 1060 300,000 96 196 384 1063 600,000 96 196 384 1065 1,000,000 96 196 384 1066

Next: Appendix D Existing Traffic Safety Data Sources »
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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 252: A Strategic Approach to Transforming Traffic Safety Culture to Reduce Deaths and Injuries provides guidance on developing a strategic approach to transform the traffic safety culture of road users and stakeholders. The goal is to use this approach to sustain improvements in traffic safety for all road users, including non-motorized users. For the purpose of this project, traffic safety culture is defined as the values and beliefs shared among groups of road users and stakeholders that influence their decisions to behave or act in ways that affect traffic safety.

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