t distribution

Description:

• From a Sample
• Based on Distribution of sample mean
• For unknown standard deviation
• In most applications, a sample size of $n\ge 30$ is adequate to use this expression
• Interval estimation: $\bar{x}\pm t_{\alpha /2}\frac{s}{\sqrt{n}}$
  • $s$ is sample standard deviation
  • $1-\alpha$ is the confidence coefficient
  • where $t_{\alpha /2}$ is $z$ with $n-1$ degree of freedom

Degree of freedom:

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