You measure the lifetime of a random sample of 25 rats that are exposed to 10 Sv of radiation (the equivalent of 1000 REM), for which the LD 100 is 14 days. The sample mean is = 13.8 days. Suppose that the lifetimes for this level of exposure follow a Normal distribution, with unknown mean μ and standard deviation σ = 0.75 day. What is the 95% confidence interval for μ based on these data?

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Answer:

CI 95%(μ)= [13.506 ; 14.094]

Step-by-step explanation:

The confidence interval (CI) formula is:

CI (1-alpha) (μ)= mean+- [(Z(alpha/2))* σ/sqrt(n)]

alpha= is the proportion of the distribution tails that are outside the confidence interval. In this case, 5% because 100-90%

Z(5%/2)= is the critical value of the standardized normal distribution. In this case is 1.96

σ= standard deviation. In this case 0.75 day

mean= 13.8 days

n= number of observations . In this case 25

Then, the confidence interval (90%) is:

CI 95%(μ)= 13.8+- [1.96*(0.75/sqrt(25)]

CI 95%(μ)= 13.8+- [1.96*(0.75/5) ]

CI 95%(μ)= 13.8+- (0.294)

CI 95%(μ)= [13.8-0.294 ; 13.8+0.294]

CI 95%(μ)= [13.506 ; 14.094]

The 95% confidence interval for μ based on the given data is; CI = (13.506, 14.094)

What is the confidence interval?

We are given;

Sample mean; x' = 13.8 days

Standard deviation; σ = 0.75 days

Sample size; n = 25

confidence level = 95%

z-score at 95% confidence level is 1.96

Formula for confidence level is;

CI = x' ± z(σ/√n)

CI = 13.8 ± 1.96(0.75/√25)

CI = 13.8 ± 0.294

CI = (13.8 - 0.294), (13.8 + 0.294)

CI = (13.506, 14.094)

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