Answer:
a) 95% Confidence interval = (0.026%, 0.037%) to 3 d.p
b) The result of the 95% confidence interval does not agree with the previous rate of such cancer because the value 0.0224% does not lie within this confidence interval obtained.
Explanation:
Confidence Interval for the population proportion is basically an interval of range of values where the true population proportion can be found with a certain level of confidence.
Mathematically,
Confidence Interval = (Sample proportion) ± (Margin of error)
Sample proportion = (131/420076) = 0.0003118483 = 0.0312%
Margin of Error is the width of the confidence interval about the mean.
It is given mathematically as,
Margin of Error = (Critical value) × (standard Error)
Critical value at 95% confidence interval for sample size of 420,076 is obtained from the z-tables because the sample size is large enough for the properties of the sample to approximate the population properties.
Critical value = 1.960 (from the z-tables)
Standard error = σₓ = √[p(1-p)/n]
n = sample size = 420,076
σₓ = √(0.0003118×0.999688/420076) = 0.0000272421 = 0.0000272
95% Confidence Interval = (Sample proportion) ± [(Critical value) × (standard Error)]
CI = 0.000312 ± (1.96 × 0.0000272)
CI = 0.000312 ± 0.0000534
95% CI = (0.0002586055, 0.0003653945)
95% Confidence interval = (0.000259, 0.000365)
95% Confidence interval = (0.0259%, 0.0365%) = (0.026%, 0.037%) to 3 d.p
b) The result of the 95% confidence interval does not agree with the previous rate of such cancer because the value 0.0224% does not lie within this confidence interval obtained.
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