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     When we look at a small sample of events that occur we sometimes mistake the  empirical results for that of the true theoretical probability of the event.   When a baby is born a boy does that mean that the baby had a 100% chance of being a boy at conception?  Genetic evidence tells us no.  Each sex has a 50/50 chance of happening at conception.  Should, therefore, a hospital which has 10 births a week be judged to "produce" more girls than boys if during a given week only 2 boys are born?  To take it a step further, if this hospital has  a one month girl/boy ratio of 30 to 10, should it now be seen as a hospital that produces mostly girls?  No.  The students should begin to understand two things.  First, independent events do not affect the outcome of other events, nor are they affected by the outcomes of other events.  Each birth (event) has its unique probability distribution.  Students who do not understand that each event (simple or compound) has it's own probability,  will generally misinterpret results of a few events as the true probability of a single event.  Therefore, the students should learn to take into account The Law of Large Numbers: empirical probability tends toward theoretical probability as the number of events increases.  Second, students should see that a hospital which has a low number of births per week does in fact have a higher chance of deviating from the theoretical probability than a collected group of hospitals which have 500 births per week. 

*Link to the Spinner Lesson Plan or the Hospitals Lesson Plan that address this misconception.