In this thesis, several factors influencing deaf effect as indicator for IA effectiveness are studied which were (mostly) unexplored in the academic literature.
In an experiment (Chapter 2) it was tested what are the main causal effects of additional contingency factors - the organization power of the internal auditor translated in top management support and the interaction effects from the collaborative partner vs. opponent perspective. In another experiment (Chapter 3) we included nudging with descriptive social norm to test the main causal effects and interaction effects from the collaborative partner vs opponent perspective.
The results of these experiments were surprising and brought originality in this area of academic research. Our study provided interesting and surprising results from the interaction effects, indicating that top management support is not always a guarantee for reducing deafness on risk warnings of the internal auditor. While it may seem to be logical that in the high organization power conditions, decision makers are more likely to follow any advice, regardless whether the message comes from a collaborative partner or an opponent, our findings suggested that great top management support can even be contra-productive when the internal auditor is seen as a collaborative partner. Based on our study results, top management support appeared to be most useful for IA effectiveness when the internal auditor is seen as an opponent.
The findings of the second experiment indicate that nudging through descriptive social norm can be used by the internal auditor to increase IA effectiveness by overcoming the deaf effect response to their risk warnings to management. Including a descriptive social norm as part of the risk warning message of the internal auditor in our experiment appeared to be useful as it significantly reduced the deaf effect response by the message recipient. Descriptive social norm can be even more useful when the messenger is seen as a collaborative partner. When the internal auditor is seen as an opponent, nudging with a descriptive social norm is ineffective, so there is no guarantee that providing a descriptive social norm will work as intended. To our knowledge, our study is a first study within the IA effectiveness research that investigated timing in relation to IA effectiveness, thereby linking the ‘supply-side’ and the ‘demand-side’ perspective of the IA effectiveness with each other (Chapter 4 and Chapter 5). By applying Focus Groups interviews (Chapter 4) and Q methodological approach (Chapter 5), we identified what determines the right moment for the internal auditor to communicate the risk warning messages to management.
The results of these studies showed that timing is recognized by both internal auditors and management as an important factor for IA effectiveness. From these studies five ‘viewpoints’ were derived that may help internal auditors to find out the right timing to communicate the risk warning messages and hence increase IA effectiveness.

By studying IA effectiveness through deaf effect our study aimed at not only identifying additional causal factors influencing IA effectiveness, but also finding out whether deaf effect for risk warning messages of the internal auditor can be studied by applying different approaches. While most of the studies in the area of IA effectiveness have focussed on factors influencing IA effectiveness such as e.g. realisation of the audit plan, number of issued reports, implemented recommendations and the like, our study made a first step towards investigating how other, more behavioural related factors may be of benefit to the IA effectiveness. The studies in this thesis demonstrate that such factors like top management support, nudging and timing can be important for IA effectiveness and that internal auditors should look ‘out of the box’ to look for other, innovative ways to increase effectiveness.

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H.R. Commandeur (Harry) , A.L.P. Nuijten (Arno)
Erasmus University Rotterdam
Erasmus School of Accounting and Assurance (ESAA)

Verbraak-Kolevska, V. (2018, October 19). Internal Audit Effectiveness : Factors influencing management to listen to the internal auditor’s risk warnings : A multi-method study from a behavioural decision making perspective. Retrieved from