A pharmaceutical company is testing a new vaccine to protect against a virus. The company selects 1,000 18-25 year-olds to administer the vaccine to and then follows the sample over the course of 3 months. Half of the sample is randomly assigned to be given a placebo (inactive) vaccine and the other half of the sample is given the active vaccine. At the end of the study, only a small percentage of the group given the active vaccine has contracted the virus or shown any adverse side effects to the vaccine, while a significant percentage of the placebo group has contracted the virus. The pharmaceutical company concludes the vaccine is safe and effective and begins the process of distributing the vaccine to the general population. Is this study high or low in interval validity? Is this study high or low in external validity?