Final answer:
To create a 99 percent confidence interval, calculate the standard error and margin of error. Factors that could affect the survey's outcome include non-response bias, response bias, sampling bias, and measurement errors. If the confidence level decreased to 90 percent, the interval would become narrower.
Step-by-step explanation:
To create a 99 percent confidence interval for the true proportion of American adults who download music weekly, you would need to know the sample size and the number of individuals in the sample who download music weekly. With this information, you can calculate the standard error and then use it to determine the margin of error. The confidence interval can be calculated by taking the sample proportion and adding and subtracting the margin of error.
Factors that could affect the survey's outcome but are not covered by the margin of error include non-response bias, where some individuals may choose not to participate in the survey, and response bias, where individuals may give inaccurate or misleading answers. Other factors include sampling bias, where the sample may not accurately represent the population, and measurement errors, where errors may occur in the data collection process.
If the confidence level decreased from 99 percent to 90 percent, the confidence interval would become narrower. This means that the range of values within the interval would decrease, providing a more precise estimate of the true proportion of American adults who download music weekly.