The 2016 Q1 earnings season takes center stage with Alcoa's (AA – Analyst Report) release after the close on Monday. Alcoa isn't the overall first to report Q1 results, though it is the first S&P 500 member with a fiscal March quarter to come out with results. Companies with fiscal quarters ending in February have been reporting in recent days, with 15 such S&P 500 members having reported results already. All of these results form part of our 2016 Q1 tally.

In fairness to Alcoa, market participants see the aluminum producer's earnings report as the starting point of each reporting cycle even though the list of early reporters such bellwethers as FedEx (FDX), Nike (NKE) and others have already reported. In total, we will see results from 7 S&P 500 members the rest of this week, with 13 index members on deck to report results next week. The chart below shows the weekly calendar of Q1 earnings reports for the S&P 500 index.

Here are four key points to know about this earnings season.

First, estimates remain low, having fallen sharply over the last three months. Total earnings for the quarter are expected to be down -10.3% on -2% lower revenues and modestly higher margins. Earnings growth is expected to be negative for 11 of the 16 Zacks sectors, including technology and Finance, the two largest in the index.

Second, the negative earnings growth in Q1 will be the fourth quarter in a row of earnings declines for the S&P 500 index. The headwinds remain unchanged from other recent periods, essentially a combination of Energy sector weakness, the dollar strength and global growth constraints. Please note that Q1 earnings growth would be in the negative even on an ex-Energy basis.

Third, the magnitude of negative revisions that Q1 estimates suffered over the last three months has been the highest of all recent quarters in the comparable periods. Fresh weakness in oil prices at the start of the period was no doubt a big driver of pushing estimates down. But Energy isn't the only sector that suffered negative revisions. In fact, estimates fell for 15 of the 16 Zacks sectors since the start of the period.