Finance is a field closely related to accounting that deals with the allocation of assets and liabilities over time under conditions of certainty and uncertainty. Finance also applies and uses the theories of economics at some level. Finance can also be defined as the science of money management. A key point in finance is the time value of money, which states that purchasing power of one unit of currency can vary over time. Finance aims to price assets based on their risk level and their expected rate of return. Finance can be broken into three different sub-categories: public finance, corporate finance and personal finance. Ethical issues in the financial services industry affect everyone, because even if you don't work in the field, you are a consumer of the services. Review articles are the summary of current state of understanding on a particular research topic. They analyze or discuss research previously published by scientist and academicians rather than reporting novel research results. Review article comes in the form of systematic reviews and literature reviews and are a form of secondary literature. Systematic reviews determine an objective list of criteria, and find all previously published original research papers that meet the criteria. They then compare the results presented in these papers. Literature reviews, by contrast, provide a summary of what the authors believe are the best and most relevant prior publications. The concept of "review article" is separate from the concept of peer-reviewed literature. It is possible for a review to be peer-reviewed, and it is possible for a review to be non-peer-reviewed.