Confidence Intervals for Proportions

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What is a confidence interval?

Back

A confidence interval is a range of values, derived from a data set, that is likely to contain the true value of an unknown population parameter, with a specified level of confidence.

Front

What does the term 'proportion' refer to in statistics?

Back

In statistics, a proportion is a type of ratio that compares a part to the whole, often expressed as a fraction, decimal, or percentage.

Front

How do you calculate the sample proportion (p̂)?

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The sample proportion (p̂) is calculated by dividing the number of successes (e.g., individuals with a certain characteristic) by the total number of observations in the sample.

Front

What is the formula for a confidence interval for a proportion?

Back

The formula for a confidence interval for a proportion is: p̂ ± Z * √(p̂(1-p̂)/n), where p̂ is the sample proportion, Z is the Z-score corresponding to the desired confidence level, and n is the sample size.

Front

What is the Z-score for a 99% confidence level?

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The Z-score for a 99% confidence level is approximately 2.576.

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What is the Z-score for a 90% confidence level?

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The Z-score for a 90% confidence level is approximately 1.645.

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What does a 95% confidence interval imply?

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A 95% confidence interval implies that if we were to take many samples and build a confidence interval from each sample, approximately 95% of those intervals would contain the true population parameter.

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How do you interpret a confidence interval of (0.652, 0.868)?

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A confidence interval of (0.652, 0.868) suggests that we are 99% confident that the true proportion of the population lies between 0.652 and 0.868.

Front

What is the relationship between sample size and the width of a confidence interval?

Back

As the sample size increases, the width of the confidence interval decreases, leading to a more precise estimate of the population parameter.

Front

What is the significance of the point estimate in a confidence interval?

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The point estimate is the best single estimate of the population parameter, typically represented by the sample proportion (p̂), and is the midpoint of the confidence interval.