Nervous and Endocrine Systems

DATA ANALYSISRelationships Between VariablesWhen scientists analyze their data, they must remember that just because two variablesare related, it does not mean that one caused the other to change. A causation occurswhen a change in one variable was caused by the other. Sometimes the cause of change ina variable may be the result of a third, unknown variable. A correlation occurs whenscientists find that two variables are closelyrelated, but the change in one variable didnot definitely cause the change in theother. When a strong correlation existsbetween two variables, scientists willconduct other experiments to discoverexactly how the variables are related.EXAMPLEScientists studied the memory of peoplewho regularly used the illegal drugecstasy. They found that ecstasy userswere more forgetful than people whodidn’t use ecstasy. Therefore, ecstasy useand memory loss are correlated. However,scientists do not know that ecstasycauses forgetfulness. It could be thatpeople who are forgetful use ecstasy.CORRELATION OR CAUSATIONGRAPH 1. ECSTASY AND MEMORYRate of forgetfulnessHighLowShort-termmemoryLong-termmemoryControlEcstacyusersSource: T. M. Heffernan, et al., HumanPsychopharmacol Clinical Experiments 2001:16.DATA ANALYSISClassZone.comDETERMINE CORRELATION OR CAUSATIONA panic attack is characterized by a sudden increasein pulse and anxiety. The graph on the right showshypothetical data for the incidence of panic attacksin the general population and in a population ofpeople who have a disorder called mitral valveprolapse, in which a heart valve does not workproperly.1. Analyze Does a correlation or a causation existbetween mitral valve prolapse and panicattacks? How do you know?2. Evaluate Can you conclude that mitral valveprolapse causes panic attacks? Why or why not?GRAPH 2. MITRAL VALVE PROLAPSE ANDPANIC ATTACKSPercent with panic attacks6050403020100ControlPeople with mitralvalve prolapseChapter 29: Nervous and Endocrine Systems 895