Management & Marketing (2008) Vol. 3, No. 3, pp. 87-96. ON A MODEL REGARDING THE PRODUCT LIFE CYCLE Alexandru ISAIC-MANIU Academy of Economic Studies, Bucharest Viorel Gh. VODĂ „Gh. Mihoc – C. Iacob” Institute of Mathematical Statistics and Applied Mathematics of the Romanian Academy Abstract. In this paper we analyze a modified model for the so-called PLC – Product Life Cycle, the original model being proposed by N. Al. Pop (2000). This PLC is considered here from a reliability theory viewpoint: our modification lies in the fact that the PLC - curve is transformed in a probability density function which allows the application of statistical inferential procedures. Key words: average sales, PLC – Product Life Cycle, PLC – curve, Pop’s model, reparametrization, pdf – probability density function. 1. Introduction According to Enciclopedia calitatii (2005, p. 135), by „product life cycle” we understand the deployment of successive and interrelated phases regarding the accomplishment and use of a product, starting from the acquisition of raw materials and/or materials (components) necessary to the manufacturing process – including the exploitation of some natural resources – and finishing with the phase of post- utilization. There are two main directions in approaching this concept: the first is given by the theories and practices of marketing and the second is imposed by the aspects regarding the viability of the product. Another important fact is that we also have the concept and in the same time the activity called „life cycle analysis”. The concept/notion derived from the idea that a product generically represents a multitude of elements both concrete and abstract that define the claims of a consumer/user (also generically!) towards a certain product – regarding the effective characteristics (physical, of use) as well as regarding the expectations referring to use and, ulterior, to the satisfaction, the degree of „contentment” achieved after using that product. Because of the fact that the economic context where we stand is supposed –at least theoretically – to be the one of a market economy, the demand for a product, its acceptance and evolution on this market tends to register, in a considerable degree, a predictable trend, called life cycle. This cycle consists of several phases, generally four or five – for example: the introduction (on the market), the growth, the maturity, the saturation and the decline. Some authors (Drăgan and Demetrescu, 1998) also take into consideration the phase of disappearance from the market of a product due to objective causes or to deliberate interventions of certain economic „actors”. All these phases (the number is not important!) refer to the actual selling process.