If a 95% confidence interval for prevalence of cancer smokers aged> 65 years is 56% to 76%, the chance that the prevalence could be less than 56% is-
**Core Concept**
A confidence interval (CI) is a statistical tool used to estimate a population parameter (in this case, the prevalence of cancer among smokers aged >65 years) based on a sample of data. The CI provides a range of values within which the true population parameter is likely to lie, with a specified level of confidence (in this case, 95%).
**Why the Correct Answer is Right**
The 95% CI from 56% to 76% indicates that we are 95% confident that the true prevalence of cancer among smokers aged >65 years lies within this range. The lower bound of the CI (56%) represents the point at which the null hypothesis of a lower prevalence would be rejected, and the alternative hypothesis of a higher prevalence would be accepted.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the CI does not provide a direct probability of the prevalence being less than 56%. The CI is a range of values, not a probability distribution.
**Option B:** This option is incorrect because the CI is a statement of confidence, not a probability. The 95% confidence level does not mean that there is a 95% chance that the true prevalence is less than 56%.
**Option C:** This option is incorrect because the CI is symmetric around the point estimate (mean or median) of the sample data. The CI is not a probability distribution, and the probability of the true prevalence being less than 56% cannot be directly read from the CI.
**Option D:** This option is incorrect because the CI is a statement of confidence, not a probability. The 95% confidence level does not mean that there is a 95% chance that the true prevalence is less than 56%.
**Clinical Pearl / High-Yield Fact**
When interpreting confidence intervals, remember that the width of the CI is inversely related to the sample size. A narrower CI indicates greater precision, while a wider CI indicates greater uncertainty.
**Correct Answer:** . The correct answer is not provided as it is not possible to determine the correct answer without knowing the correct option.