\[n \ge \left( \frac{z_c \sigma}{E}\right)^2 \] If you are dealing with a population proportion instead of a population mean, you should use instead our minimum required sample size calculator for proportions . And now we're ready to calculate the confidence interval, confidence interval. It is going to be equal to our sample proportion plus or minus our critical value, our critical value, times the standard deviation of the sampling distribution of the sample proportion. Now there is a way to calculate this exactly if we knew what p is. In both confidence interval formulas Z is the score statistic, corresponding to the desired confidence level. The Z-score corresponding to a two-sided interval at level α (e.g. 0.90) is calculated for Z 1-α/2, revealing that a two-sided interval, similarly to a two-sided p-value, is calculated by conjoining two one-sided intervals with half This statistics video tutorial explains how to find the z-score that will be used to find the confidence interval and margin of error for a population mean. Jul 9, 2021 · 99%. 2.58. To calculate a CI for a population proportion: Determine the confidence level and find the appropriate z* -value. Refer to the above table for z *-values. Find the sample proportion, ρ, by dividing the number of people in the sample having the characteristic of interest by the sample size ( n ). Note: This result should be a decimal Nov 3, 2015 · Its z value is 2.33. Answer link. z - score for 98% confidence interval is 2.33 How to obtain this. Half of 0.98 = 0.49 Look for this value in the area under Normal curve table. The nearest value is 0.4901 Its z value is 2.33. .

critical z score for 99 confidence interval