One strength is case study evidence of different types of long term memory. Clinical studies of amnesia showed both participants had difficulty recalling events that had happened to them in their pasts (episodic memory). But their semantic memories were unaffected. Procedural memories were also intact. This supports the view that there are different memory stores in long term memory as one store can be damaged but other stores are unaffected. However, researchers lack control in clinical studies as they don't know about the participants memory before the brain damage.