So far this year, the S&P 500 is up 2%, while the average stock in the Russell 3,000 (an index that contains large-cap, mid-cap, and small-cap stocks) is up 0.9%. These performance numbers highlight how the largest stocks in the market have boosted the performance of major indices.

There are some big discrepancies when you look at cap-weighted S&P 500 sector performance versus the performance of the average stock in each Russell 3,000 sector. One of the biggest standouts is the Consumer Discretionary sector. As shown in the chart below, the S&P 500 Consumer Discretionary sector is up 6.3% year-to-date. That’s the second-best performing sector in the market. In the Russell 3,000 Consumer Discretionary sector, though, the average stock is actually down 0.1% year-to-date. The significant underperformance on an equal-weight basis suggests that Consumer Discretionary is much weaker than it appears underneath the surface. The two main stocks causing this discrepancy are Netflix (NFLX) and Amazon (AMZN). Given their massive market caps, their movements have a huge impact on the S&P 500 Consumer Discretionary sector.With NFLX up 69% YTD and AMZN up 31%, these two stocks account for nearly all of the cap-weighted sector’s YTD gains.

The opposite trend is in place for the Health Care sector.Here we’ve seen the largest Health Care stocks lag the smaller ones year-to-date. The S&P 500 Health Care sector is up 1.8% in 2018, while the average Health Care stock in the Russell 3,000 is up 7.4%. This suggests that the Health Care sector has actually been performing better than it appears. The same is true for Consumer Staples based on the data points in the chart.

For Technology, we’ve seen strength across all market cap levels. The S&P 500 Technology sector (cap-weighted) is up 7.9% year-to-date — the best of any sector. The average Technology stock in the Russell 3,000 is also up 7.9% — the best of any sector. You won’t find any weakness underneath the surface for Tech at this point.