A directionality problem is known in psychology and is a common issue in correlational studies. It can be defined as when the cause and effect of two variables is not known. In this case, some of the studies leave confusion as to which one caused the other. Did teenagers become pregnant because of their substance use or did a teenage pregnancy leave to increased substance use? This was said about The American Journal of Drug and Alcohol Abuse study discussed in the teenage pregnancy page. But it cannot be that simple? There must be something missing? This is called a third variable problem, when there is a missing link between two factors. What cause the increased substance use? Or what caused the teenagers to be riskier in their sexual behavior? Was its parental influence? Peers? School or Work? Possibly but that is unknown and can only be inferred. And whether the missing link was before, in between or after the use or the sexual behavior is also unknown in many of these cases. Both of these problems are ones that psychologist struggle with when establishing a correlational study.