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Standard estimation of ARMA models in which the AR and MA roots nearly cancel, so that individual coefficients are only weakly identified, often produces inferential ranges for individual coefficients that give a spurious appearance of accuracy. We remedy this problem with a model that uses a simple mixture prior. The posterior mixing probability is derived using Bayesian methods, but we show that the method works well in both Bayesian and frequentist setups. In particular, we show that our mixture procedure weights standard results heavily when given data from a well-identified ARMA model (which does not exhibit near root cancellation) and weights heavily an uninformative inferential region when given data from a weakly-identified ARMA model (with near root cancellation). When our procedure is applied to a well-identified process the investigator gets the “usual results,” so there is no important statistical cost to using our procedure. On the other hand, when our procedure is applied to a weakly identified process, the investigator learns that the data tell us little about the parameters – and is thus protected against making spurious inferences. We recommend that mixture models be computed routinely when inference about ARMA coefficients is of interest.

This paper aims to examine the Treasury bond yields response to monetary policy shocks in Tunisia under a heterogeneous economic environment.

Using a traditional fixed coefficient model, the impact of monetary policy changes on the term structure of interest rates for the whole period from January 2006 to December 2016 is estimated first. Then the stability of this relationship by distinguishing two sub-periods around the revolution of January 2011 is studies. To investigate how the relationship between the monetary policy and the Treasury yield curve evolves over time, a time-varying parameter model is estimated.

The results show that the impact of monetary policy is more pronounced at the short end of the yield curve relative to the longer end. Furthermore, this impact declines significantly across all maturities following the revolution and exhibits wide time variation. This evidence supports the negative influence of high levels of uncertainty on monetary policy effectiveness and highlights the desirability of more active monetary policy, especially in turbulent environment.

The impact of uncertainty on the effectiveness of monetary policy shocks needs to be explored further in future research to understand the structural sources of uncertainty and their dynamic interactions with monetary policy and risk aversion in asset markets.

A more active role of the central bank to influence the yield curve mainly through Treasury bond purchases covering medium and long maturities may be warranted. Communication also needs to be reinforced to ensure predictability of the monetary policy stance.

This paper extends the empirical literature on the pass-through of monetary policy to interest rates for an emerging country in context of transition by estimating a state-space model to test the time-varying behavior and examine the influence of increased economic uncertainty on monetary policy effectiveness.