Blind trials mean that the subject of the experiment (the patient) does not know if they are in the experimental group or control group, only the technician knows this. A double-blind trial means both the subject and the technician do not know which group the subject is in. Drug companies use double-blind trials to test new medications.
Animal models, like rats and mice, can be used to test new drugs or conduct experiments. Rats and mice are mammals, like us, so many drugs that are toxic to them would also be toxic to humans.
Correlations, or relationships between two variables, can indicate a connection. For example, people with higher stress levels have more colds. (Fig 1.11). However correlation does not mean that stress actually causes the cold. The cold is caused by a virus. Stress lowers your immune system, so it is harder for the body to fight the virus.
Sample size : when you conduct a scientific experiment, the larger the sample the more accurate the results.
Theory : a scientific theory has been supported by many experiments: like atomic theory, cell theory, germ theory, and the theory of evolution. Note that this is very different from the common use of the word theory. In everyday life, theory just means a vague idea or guess, whereas a scientific theory has been tested many times, and no evidence has been found to disprove it. In other words a scientific theory is based on a lot of information and is very solid.