Proxy: OECD publishes no euro-area aggregate in its current leading-indicator release. This is the four major European economies (Germany, France, Italy, Spain).
The OECD's amplitude-adjusted leading indicator for the four largest euro-area economies, which together are three quarters of euro-area GDP. Below 100 and falling means growth is expected to run under trend and the gap is widening.
Threshold source: OECD: 100 is the long-term trend. How thresholds are chosen
A proxy, not the euro area. Revised for several months after first publication.