Definition of statistical difference? Definition of a true experiment?

This is my first psychology class and I'm lost......Definition of statistical difference? Definition of a true experiment?
In psychology, alpha levels are most commonly set at .01 (more stringent) and .05 (a bit less stringent) to determine whether or not a statistically significant differences exist.





True experiments must include random assignment of participants, typically sport a at least one control group and one experimental group (in some designs, each subject serves as his/her own control), and examine at least one independent and one dependent variable.





~M~