Question

A traffic engineer recently found that the average morning commute time from Los Lunas to Albuquerque was 30 minutes. A previous study conducted in 1990 found the same average morning commute time to be 22 minutes. Does the difference of eight minutes prove that the average morning commute really is longer? Explain.

Answer 1

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Mean = 30 min

Previous mean = 22 min

Is the difference of 8 minutes prove commute really is longer ? We can't say a yes or no. It really is dependent on the standard deviation, which if very large means that the value of mean of 22 minutes may vary hugely and therefore may have number of instances where time taken was above 30 minutes. Hence, the difference of 8 minutes can't prove that the average morning commute really is longer, until we get the standard deviation of morning commute time.