The preliminary flash data for the July-September period showed a surprisingly strong 0.4 percent quarterly rise in GDP, double both the market consensus and the unrevised second quarter rate. Annual growth was 0.9 percent, up from 0.6 percent previously.

Within the region's quarterly advance, France expanded 0.4 percent, in large part due to the effects of the Paris Olympics, and Spain a solid 0.8 percent, matching its second quarter gain. Germany surprised on the upside with a 0.2 percent rise, although this followed a weaker revised second quarter, while Italy disappointed as GDP only stagnated. Elsewhere, Ireland climbed fully 2.0 percent and Lithuania 1.1 percent but Latvia remained in recession with a 0.4 percent contraction. There were no other outright declines.

Lacking any expenditure components, the provisional headline third quarter data probably flatter to deceive and conceal another quarter of sluggish private sector domestic demand. In any event, they are not strong enough to undermine expectations for another cut in ECB interest rates in December. That said, today's reports lift the Eurozone RPI to 6 and the RPI-P to 8, both measures showing a marginal degree of overall economic underperformance versus market expectations.

The preliminary flash report is expected to put quarterly growth at 0.2 percent, unchanged from the downwardly revised final second quarter rate, and the yearly change at 0.8 percent, up from 0.6 percent.

Gross domestic product (GDP) is the broadest measure of aggregate economic activity and encompasses every sector of the economy. There are two preliminary estimates which are based on only partial data. The first is the preliminary flash, introduced in April 2016 and limited to just quarterly and annual growth statistics for the region as a whole. This is issued close to the end of the month immediately after the reference period. The second flash report, released about two weeks later, expands on the first to include growth figures for most member states but still provides no information on the GDP expenditure components.

GDP is the all-inclusive measure of economic activity. Investors need to closely track the economy because it usually dictates how investments will perform. Stock market Investors like to see healthy economic growth because robust business activity translates to higher corporate profits. The GDP report contains information which not only paints an image of the overall economy, but tells investors about important trends within the big picture. These data, which follow the international classification system (SNA93), are readily comparable to other industrialized countries. GDP components such as consumer spending, business and residential investment illuminate the economy's undercurrents, which can translate to investment opportunities and guidance in managing a portfolio.

Each financial market reacts differently to GDP data because of their focus. For example, equity market participants cheer healthy economic growth because it improves the corporate profit outlook while weak growth generally means anemic earnings. Equities generally drop on disappointing growth and climb on good growth prospects.

Bond or fixed income markets are contrarians. They prefer weak growth so that there is less of a chance of higher central bank interest rates and inflation. When GDP growth is poor or negative it indicates anaemic or negative economic activity. Bond prices will rise and interest rates will fall. When growth is positive and good, interest rates will be higher and bond prices lower. Currency traders prefer healthy growth and higher interest rates. Both lead to increased demand for a local currency. However, inflationary pressures put pressure on a currency regardless of growth.