Answer :
The proportion that is at most 2.33 standard deviations above average in a normal distribution corresponds to a confidence level of 2) 99%.
Therefore, the confidence interval you calculate by going 2.33 standard deviations on either side would be a 99% confidence interval.
The constructing confidence intervals using a normal distribution. A 95 percent confidence interval typically captures the true population parameter within two standard deviations of the sample mean.
In a standard normal distribution, if the area within 2.33 standard deviations from the mean corresponds to a 99% probability.
Then when constructing a confidence interval that extends 2.33 standard deviations on either side, we would actually capture 99% of the data (2.33 standard deviations would be the critical value).
Therefore, since a 95% confidence interval extends about 1.96 standard deviations from the mean and captures 95% of the data, a 2.33 standard deviation interval would be wider and hence correspond to a higher confidence level.
Based on the question, since the interval includes 99% in the middle and excludes 1% (divided into two tails of 0.5%), the interval would correspond to a 2) 99% confidence interval.
