Two data sets, each with 10 integers, are summarized. Data Set P has 4 integers in the interval greater than or equal to 10 but less than 20, and 6 integers in the interval greater than or equal to 20 but less than 30. Data Set Q has 4 integers in the interval greater than or equal to 0 but less than 10, and 6 integers in the interval greater than or equal to 10 but less than 20. What is the smallest possible difference between the mean of Data Set P and the mean of Data Set Q?