Which experimental methods is not considered difficult to replicate? participant observation
controlled observation
unstructured interview
naturalistic observation

When analyzing tree rings, what do scientists assume a thin ring indicates?

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.

At which point is crust neither created nor destroyed? island chain mid-ocean ridge divergent boundary transform boundary