It's a mixture of describe and explain...so say what you see (give some figures if appropriate) and give an explanation to why this is so or why something has happened. It also requires a bit of your own opinion so at the end I would use your own knowledge to evaluate what you think about it. E.g. without an opinion you might say 'this could have happened due to inflation, unemployment and growth' but when they ask for your own opinion you should say something like 'it could have happened due to inflation, unemployment and growth but I think it is most likely due to growth because I know that blah blah blah....'
