Inferential Statistics

timer Asked: Jun 20th, 2015

Question description

  1. In previous problems, we have been concerned with finding a 95% confidence interval for a population proportion. Although a 95% confidence interval is most common (public opinion polls use it almost exclusively), other confidence intervals are easy to define and calculate. We know that a 95% confidence interval contains the values that are within 2 standard errors of the sample proportion because the distribution of sample proportions is assumed to be normal, and 95% of the sample proportions are within 2 standard errors (standard deviations) of the population proportion. Similarly, we can define a 99.7% confidence interval, which would be based on 3 standard errors, since 99.7% of all sample proportions are within 3 standard errors of the population proportion. Other commonly used confidence intervals are a 99% confidence interval based on 2.58 standard errors and a 90% confidence interval based on 1.65 standard errors.

    In some opinion poll, out of a sample of 1,370 adults nationwide, 42% supported a complete ban on all research into human cloning, without exception.

    Find a 90% confidence interval for the proportion of adults who support a complete ban on all research into human cloning. Please round the answers to the nearest tenth.


38.7% to 44.2%


39.8% to 44.2%


38.0% to 46.0%


39.8% to 45.3%


38.7% to 45.3%

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