Identifiers　chosen　by　programmers　convey　rich　semantic　information　that　could　be　exploited　to　enhance　program　analysis　for　various　software　engineering　tasks,　e.g.,　anomaly　detection,　argument　recommendation,　and　code　completion.　However,　such　information　has　not　yet　been　fully　exploited,　and　little　is　known　about　its　properties.　In　this　paper,　we　carry　out　an　empirical　study　to　investigate　the　lexical　similarity　between　the　actual　argument　and　the　formal　parameter　names　in　method　invocations.　By　analyzing　actual　arguments　and　formal　parameters　from　127　Java　applications　and　30　open-source　C　applications,　we　observe　a　number　of　interesting　and　valuable　findings　concerning　the　distribution　of　similarity,　reasons　for　dissimilarity,　and　so　on.　Such　findings　have　been　exploited　to　facilitate　argument-related　software　engineering　tasks,　i.e.,　anomaly　detection　and　code　completion.