The song says a spoonful of sugar helps the medicine go down.  But a new study says that kind of imprecise measurement for the medicine itself can lead to potentially dangerous mistakes.  The results underscore recommendations from government agencies and medication safety groups that say milliliters should become the standard measurement unit for liquid medicines.  The study involved nearly 300 parents with children younger than 9 years old who were treated for illnesses that required prescription medicine.  Parents who used spoonfuls were 50 percent more likely to give incorrect doses than those who measured in more precise units.  The results were released online Monday in Pediatrics.