Margin of Error If an experiment only has two choices, then a rule of thumb for

Question

Margin of Error

If an experiment only has two choices, then a rule of thumb for the margin of error is that the margin of error is approximately twice the standard error.

Previous records show that among people who were in prison for a drug offense and then released, 78.8% were re-arrested within 5 years.

Find the margin of error in the proportion of re-arrested prisoners in a study of 307 prisoners.

Note: This is not the same question as the maximum margin of error. Give answer as a proportion, not a percent! Round to 4 decimal places if needed.

Explanation / Answer

p = 0.788 , n = 307

we calculate mrgin of error for z value at 95% = 1.96

margin of error = z * sqrt (p *(1 -p)/n)
= 1.96 * sqrt( 0.788 * ( 1 -0.788)/307)
= 0.0457
  
  

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