Reviews

Successful Instructional Diagrams by Ric Lowe, London, Kogan Page, 1993. ISBN: 0–7494–0711–5

Reviews

Technology‐based Learning Environments: Psychological and Educational Foundations edited by S. Vosniadou, E. De Corte and H. Mandl, volume 137 in NATO ASI Series F (Computer and Systems Sciences), Berlin, Springer‐Verlag, ISBN: 0–387–58253–3, 1994

Testing for Instability in Factor Structure of Yield Curves

A widely relied upon but a formally untested consideration is the issue of stability in actors underlying the term structure of interest rates. In testing for stability, practitioners as well as academics have employed ad hoc techniques such as splitting the sample into a few sub-periods and determining whether the factor loadings have appeared to be similar over all sub-periods. Various authors have found mixed evidence on stability in the actors. In this paper we develop a formal testing procedure to evaluate the factor structure stability of the US zero coupon yield term structure. We find the factor structure of level to be unstable over the sample period considered. The slope and curvature factor structures are however found to be stable. Common structural changes affecting all interest rate maturities have fostered instability in the level factor. We corroborate the literature that variances (volatility) explained by the level, slope, and curvature factors are unstable over time. We find that the volatility of slope factor is sensitive to shocks affecting the short rates and the volatility of curvature factor is sensitive to shocks affecting the medium and long rates. Finally, we find evidence of the presence of common economic shocks affecting the level and slope factors, unlike slope and curvature factors that responded differently to economic shocks and were unaffected by any common instabilities

Modelling the Diffusion of Scientific Publications

This paper illustrates that salient features of a panel of time series of annual citations can be captured by a Bass type diffusion model. We put forward an extended version of this diffusion model, where we consider the relation between key characteristics of the diffusion process and features of the articles. More specifically, parameters measuring citations’ ceiling and the timing of peak citations are correlated with specific features of the articles like the number of pages and the number of authors. Our approach amounts to a multi-level non-linear regression for a panel of time series. We illustrate our model for citations to articles that were published in Econometrica and the Journal of Econometrics. Amongst other things, we find that more references lead to more citations and that for the Journal of Econometrics peak citations of more recent articles tend to occur later