This thesis deals with various issues regarding determinants of US corporate credit spreads. These spreads are estimated as the difference between yields to maturity for corporate bonds and default-free instruments (Treasury bonds) of the same maturity. Corporate credit spreads are considered as measures of default risk. However, the premium required by investors for holding risky rather than risk-free bonds will incorporate a compensation not only for the default risk but also for other factors related to corporate bonds such as market liquidity or tax differential between corporate and Treasury bonds. In this study we firstly examine the relationship between bond ratings and credit spreads given that bond rating changes are expected to carry some informational value for debt investors. The findings indicate that bond ratings generally carry some informational value for corporate bond investors. The Granger causal relationship is more evident for negative watch lists and during periods of uncertainty in financial markets. In line with previous studies, our results suggest that changes in credit spreads are significantly related to interest rate levels, systematic risk factors (Fama and French) factors and equity returns.

The modelling of stock market volatility is considered to be important for practitioners and academics in finance due to its use in forecasting aspects of future returns. The GARCH class models have now firmly established themselves as one of the foremost techniques for modelling volatility in financial markets. The application of GARCH class models in developed and emerging markets (including the Egyptian Stock Market) provides evidence of GARCH effects in stock returns. However, most of the studies conducted on modelling the volatility of stock returns are based on the aggregated market index. This thesis argues that this will not reflect significant differences of variation in the pattern of volatility associated with different stocks. However, in order to examine the similarities and differences between the conditional variance structures of stocks from the same or different industries in the same equity market, this thesis estimates pooled-panel models. These novel models are used to test for similarities and differences in the conditional variance equation in panels of time series within a general to specific framework of nested tests. This is done using panel samples of sector indices and stocks from the Egyptian Stock Market covering the period from 1997 to 2002. The results suggest that there are similarities in the temporal volatility structures of stocks from the same sector or industry, but there are significant differences in the temporal volatility structures of stocks from different sectors or industries. This suggests that using indices alone for modelling the volatility of an equity market, which is the method used in the majority of studies cited in the literature, may not be appropriate. The thesis concludes with a discussion of some of the implications of these results and suggestions for further research. / Doctor of Philosophy (PhD)

This thesis focuses on the relationship between short-term interest rate and stock prices. The main idea is that if interest-rate increases, it makes holding stocks less attractive relative to fixed income securities. Therefore, investors change the structure of their portfolios and switch capital from stocks to banks, which results in stock prices decrease. In our thesis, we apply GJR-GARCH-t-M model to study the impact of Czech interest rate (14-day PRIBOR) on the Prague Stock Exchange (the PX index). In contrast to the majority of research on this topic, we have found no impact of the PRIBOR rate on the PX index- neither on its mean nor on its volatility. We attribute the absence of a significant relationship to exceptional composition of the PX index. Furthermore, we have found that the recent crisis has significantly changed the behavior of the Czech stock market.

This thesis analyzes the effect of the Czech National Bank's (CNB) communica- tion on the interest rate volatility (PRJBOR reference rate). Starting with the literature survey about the central bank communication in the world, I focus on the literature that concerns the CNB. To model the CNB's communication, I use the GARCH(l,1), EGARCH(l,1) and TARCH(l,1) models. I have created a unique data set containing the dummy variables for the CNB communication. The results are as follows: (a) the CNB's communication tends to decrease the volatility, (b) timing of the communication has a key role as the comments closer to the meeting have bigger calming effect, and that (c) there is no clear effect concerning the comments of the Bank Board members in the media. JEL Classification Keywords E43, E44, E52, E58 Czech National Bank, monetary policy signaling, central bank communication, the term structure of interest rates, GARCH analysis Author's email karasp@email.cz Supervisors's email roman. horvath@gmail.com