Credit and Market Risks
Balance sheet items that potentially subject us to concentrations of credit risk are primarily cash and cash equivalents, short-term marketable securities, accounts receivable and expenditures billable to clients. We invest our cash primarily in investment-grade, short-term securities and limit the amount of credit exposure to any one counterparty. Concentrations of credit risk with respect to accounts receivable are mitigated by our large number of clients and their dispersion across different industries and geographic areas. We perform ongoing credit evaluations on a large number of our clients and maintain an allowance for doubtful accounts based upon the expected collectability of all accounts receivable.
Our pension plan assets are also exposed to market risk. The fair value of our pension plan assets may appreciate or depreciate during the year, which can result in lower or higher pension expense and funding requirements in future periods.