Filtering on

"Aspirin is no better than a placebo. I used to give my sister bread pills when she asked me to get her aspirin, and she always said how much better they made her feel and never noticed the difference."

"Our analyses of 833 diverse middle schoolers found that most of them learned better with hands-on activities. But we can't conclude anything about children who weren't in our study, because we didn't collect any data about them."

"Eighty percent of people who took the drug got better. But the drug didn't really work, because a quarter of people who took the placebo got better even though they didn't take the drug, and twenty percent of people who took the drug didn't get any better at all."  

"RCTs cannot give sufficient evidence for causation that salt causes heart disease, because there might be other factors at play."

"We should give the experimental drug to all eight hundred people in a study, instead of giving it to just half of them, because we want to maximize our sample size."

"If you give a drug to 500 people with a disease, and 80% of them get better, then we know the drug works."

a. Experimental Intervention: The act of an experimenter changing one variable in a possible causal network. 

b. Randomized Assignment: Given sufficient sample size, randomized assignment rules out confounds by  distributing variation randomly between the two groups, thereby avoiding systematic differences except as the result of the intended intervention. 

c. Control Condition: Comparison of an experimental to a control condition is necessary in order to distinguish effect of intervention from changes that would have occurred without the intervention.  

d. Sampling: A study of a well-chosen sample can tell you something about the population (through induction), especially if it was selected in such a way as to avoid any systematic differences between the sample and the rest of the population. It is often difficult or even impossible to capture a perfectly representative sample, so scientists do the best they can. For example, many psychology studies are done with college students because they are accessible, but such samples differ systematically from the general population. Inferences from samples to a larger population need to take such differences into account.