What happens if the confidence level decreases

For more information, please see our University Websites Privacy Notice. The confidence interval is the plus-or-minus figure usually reported in newspaper or television opinion poll results.

The confidence level tells you how sure you can be. It is expressed as a percentage and represents how often the true percentage of the population who would pick an answer that lies within the confidence interval.

Factors that Affect Confidence Intervals The confidence interval is based on the margin of error. There are three factors that determine the size of the confidence interval for a given confidence level. These are: sample size , percentage and population size. Sample Size The larger your sample, the more sure you can be that their answers truly reflect the population.

This indicates that for a given confidence level , the larger your sample size, the smaller your confidence interval. However, the relationship is not linear i. Optional Collaborative Classroom Exercise Exercise 1. Critical Evaluation. Solutions to Exercises in Chapter 1. Descriptive Statistics.

Descriptive Statistics: Introduction. Descriptive Statistics: Displaying Data. Descriptive Statistics: Histogram Example 2. Example 2. Optional Collaborative Exercise. The Law of Large Numbers and the Mean. Sampling Distributions and Statistic of a Sampling Distribution. Problem 1. Problem 2. Problem 3. Problem 4. Solutions to Exercises in Chapter 2. The Normal Distribution. Normal Distribution: Introduction.

Optional Collaborative Classroom Activity. Normal Distribution: Standard Normal Distribution. Normal Distribution: Z-scores Example 3.

Example 3. Normal Distribution: Areas to the Left and Right of x. Normal Distribution: Calculations of Probabilities Example 3. Examples of the Central Limit Theorem Example 3. Problem 5. The fewer dissolved solids they have, the better. When they calculate a two-sided confidence interval, the upper side of the interval is However, because the company only cares about the upper bound, they can calculate a one-sided confidence interval instead.

The one-sided confidence interval shows that the upper bound for the amount of dissolved solids is even lower, The advantage of a lower confidence level is that you get a narrower, more precise confidence interval. The disadvantage is that you have less confidence that the confidence interval contains the population parameter you are interested in.

So lower the confidence level only if, in your situation, the advantage of more precision is greater than the disadvantage of less confidence. For example, if it's too expensive to increase the sample size in your study, lowering the confidence level will shorten the length of the interval at the expense of losing some confidence. Ways to get a more precise confidence interval Learn more about Minitab.

If your confidence interval is too wide, you cannot be very certain about the true value of a parameter, such as the mean. However, you can use several strategies to reduce the width of a confidence interval and make your estimate more precise.