A TIWB Programme – like any other programme – has specific goals and objectives. These goals and objectives must be agreed upon and defined so that the effectiveness and efficiency of the work undertaken during the TIWB Programme can be valued and measured.

Measuring the impact of a TIWB Programme through the use of indicators is useful for evaluation and accountability purposes. Beyond revenue-linked targets, there are important long-term goals of effective of targeted tax audit assistance such as

• sustainable knowledge transfer
• improved consistency and fairness in audit processes
• reduced taxpayer challenges to audit outcomes
• increases in taxpayer confidence towards the Host Administration

As noted in the 2013 OECD/ITC/BMZ report, Tax and Development Aid Modalities for Strengthening Tax Systems, "Some superficially attractive indicators can be double-edged swords. The tax ratio [tax revenue to GDP] is a prominent case in point in that over-ambitious targets can lead to abusive collection practices at the expense of tax legitimacy."

The Host Administration will lead the process of establishing objectives for the TIWB Programme and selecting indicators to measure impact. This objective-setting process, including indicator selection, should be finalised in consultation with the Expert, as well as any Donor Partner or Partner Administration. The TIWB Secretariat can provide examples of programme indicators and assist the Host Administration in the objective-setting. All of the parties to a TIWB Programme should have a clear understanding of the objectives and how they will be measured in advance of the Programme. At the end of the TIWB Programme cycle, both the TIWB Expert and the Host Administration are required to submit a Final Programme Report to the TIWB Secretariat.

Recognition that the outcome and success of a TIWB programme is influenced by elements and factors which are both within and sometimes outside the control of the Expert must be considered. Ensuring an appropriate level of support for the TIWB Programme within the Host Administration – in respect to resources, personnel and support for any required changes – is crucial to success. Like the selection of objectives and impact indicators, measuring impact is the responsibility of the Host Administration, but will necessarily involve the Experts themselves.

The following are a selection of potential impact indicators that can be used or adapted to each TIWB Programme to assist in the formulation of indicators by the Host Administration. Furthermore, since impact should be assessed progressively, indicators should be tailored to consider short-, medium- and long-term objectives. It may also be appropriate to establish post-Programme objectives to ensure that measures implemented during the Programme are continued beyond the duration of the TIWB Programme. Clearly, indicators need to be adapted to take into account the scope of the particular TIWB Programme and the context of the Host Administration.

Care must be taken when selecting impact metrics, as a narrow focus on easily quantifiable indicators – such as revenue increases – needs to be balanced with more nuanced considerations. Capacity building for better quality administration and sustainability, through the transfer of practical knowledge and skills, remains the over-arching objective of any TIWB Programme. Therefore qualitative indicators are equallyrelevant than quantitative indicators; qualitative indicators bring valuable input for future development, as well as for specific measures to improve current systems and working methods. The outcome after applying qualitative indicators often proves to be more sustainable and useful for future development.

Below is a list of examples of indicators that can be used to assess the impact of TIWB Programmes. Indicators should obviously align with the Programme's stated objective(s). Depending on the situation, scope and goals of the Programme, the Host Administration can incorporate or omit certain indicators.

Some indicators target specific internal organisational measures that could be taken or developed by the Host Administration in order to reach the TIWB Programme goals. The short-term indicators are quite specific and relate more to practical day-to-day situations and issues to be dealt with by the Host Administration. The mid- and long-term indicators are targeted at monitoring the broader effects, progress and development of the Programme activities.

Impact assessment must aim to take these nuances into account while measuring the Programme's effectiveness in a concrete and meaningful way. This often means designing a balanced approach of quantitative and qualitative measures.