Available headline data are generally compiled from commercial data supplied by MSCI (www.msci.com). For the experimental European aggregates, when a country prefers a different source these data are included replacing that reported by MSCI and using the appropriate code. The data are heterogeneous in terms of the transaction or valuation based methodologies used. Therefore, comparisons between countries or of different sources within individual countries should be made with caution. The indicators are generally available at quarterly frequency. Breakdowns of the data are also available but these are strictly shown by the type of data collection i.e. transaction based or valuation based.