An economic impact assessment (EIA) is an analysis of the effects of an economic stimulus on the economy. Typically, an EIA is undertaken for major projects such as a mine, industrial plant or event so that the economic benefits can be understood and promoted. Often the economic benefits of a project are used to lobby government for support as the impacts on taxation can be readily included as part of the assessment process.

EIA's are also used to calculate negative economic impacts such as the closure of a mine and the loss of associated economic activity.

EIAs are calculated using an input-output (IO) model. At the core of an IO model is an IO table. An IO table is a matrix containing all the transactions between sectors of the economy for a financial year including inter-industry transactions, primary inputs to production and final demand for industry output. Since the IO table details the input structure of a particular industry, the effects on the economy from increasing the output of that industry can be readily estimated by solving a set of linear equations.

IO tables are time consuming, data intensive and therefore expensive to construct. Government statistics offices produce them as part of the national economic accounting structure. The most recent Australian IO Table is for 1996-97 produced by the Australian Bureau of Statistics. The Queensland Office of Economic and Statistical Research has also just released a Queensland IO Table for 1996-97 and has available a full set of integrated regional IO tables for the statistical divisions of Queensland.

The results of an EIA are generally presented as both direct effects, that is effects from the direct expenditure of the project or event and indirect effects, which are additional effects from further rounds of spending in the supply chain. A third or consumption effect, resulting from rounds of consumer spending generated by the additional income in the region can also be calculated. All effects are presented as:

• Output - the actual dollar amount spent on the project in the region under study. Spending on imports to the region are excluded since they generate no economic activity;
• Income - the amount of wages and salaries paid to labour;
• Employment - the full time equivalent per annum employment generated by the project;
• Value Added - the value added to materials and labour expended on the project; and
• Industry effects - each of the above four measures can be specified for individual industries.

With major projects, two sets of impacts are usually calculated: those from construction, which will occur over a short timeframe; and those from operation, which will occur over a longer timeframe.

AECeconomics has undertaken a vast range of EIAs including: mining projects, dam raising, environmental flows, port expansion, road construction, power stations, industrial plant, pipeline construction, office relocation, sporting events, cruise ship visits and tourism.