Market research

Chapter 19 Confidence Intervals for Proportions 339 Chapter 19 ? Confidence Intervals for Proportions 1. Margin of error. He believes the true proportion of voters with a certain opinion is within 4% of his estimate, with some degree of confidence, perhaps 95% confidence. 2. Margin of error. He believes the true percentage of children who are exposed to lead-base paint is within 3% of his estimate, with some degree of confidence, perhaps 95% confidence. 3. Conditions. a) Population ? all cars; sample ? 134 cars actually stopped at the checkpoint; p ? proportion of all cars with safety problems; p? ? proportion of cars in the sample that actually have safety problems (10.4%). Plausible Independence condition: There is no reason to believe that the safety problems