One and Two sample hypothesis tests are either comparing a sample to a standard value or comparing to samples to each other.  Thanks to the CLT and the empirical rule we can usually trust the results.  But there are exceptions.  These are called Type I and Type II errors.  So:

1. What are Type I and Type II errors?
2. Is there anything we can do to measure the likekihood of tehse errors and thereby reduce the chance of these errors occuring?