You are kidding, right? Or are you really saying that you don't know the difference between psychology and sociology. Would you ask a sociologist to organise a series of experiments in cognition or memory; or to treat an anorexic? Would you ask a Rogerian therapist to oversee a crime survey? The reason there are two different words is because they are two different things.
Doug 'Psychology is shaped by social circumstances.'
No, not wholly. Many aspects of psychology are shaped by human biology (all the lower psychological functions, according to Vygotsky). But setting that too one side, and considering that psychology that is shaped by social circumstance (and even here there are some missed out mediating factors, such as intersubjective relations). Does it follow that the one, psychology, is reducible to the other, society? Not at all. Photo-synthesis is shaped by sunlight, but it is not sunlight. Car maintenance is shaped by social circumstances, but I wouldn't ask a sociologist to fix my car.
Doug 'How can you separate them like this?'
How can you not separate them? Is everything one, to you? Is society, like Buddha, a shoreless sea? Social science tells us about society. Psychology tells us about individual thought processes. Your social science might be able to come up with some generalisation about the frequency of murder (though even there it would be little more than a statistical measure of events with too many determinants to sort out). What it could not do is predict which individual is going to commit the crime, because social science gives no access, nor pretends to give access to individual thought processes.