Confidence intervals for means
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Confidence Intervals for Means. point estimate – using a single value (or point) to approximate a population parameter. the sample mean is the best point estimate of the population mean  The problem is, with just one point, how do we know how good that estimate is?

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  • point estimate – using a single value (or point) to approximate a population parameter.

    • the sample mean is the best point estimate of the population mean 

  • The problem is, with just one point, how do we know how good that estimate is?

  • A confidence interval (or interval estimate) is a range of interval of values that is likely to contain the true value of the population parameter.

  • confidence interval = estimate  margin of error

  • common choices are:

    • 90% ( = 0.10);

    • 95% ( = 0.05);

    • 99% ( = 0.01).



Create a 95% confidence interval for the starting salaries of 20 college graduates who have taken a statistics course if the mean salary is $43,704, and the standard deviation is $9879.

  • margin of error

    s = standard deviation = $9879

    n = sample size = 20

    df= degrees of freedom = n-1=19

    tcrit=2.093


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