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.

Below is a list of the best performing Russell 3,000 stocks year-to-date. As mentioned above, Health Care looks stronger underneath the surface due to big gains on an equal-weight basis. You can see what we mean by looking at the list of best performers. They’re nearly all biotech names! Of the 30 best performing Russell 3,000 stocks year-to-date, 21 are Health Care sector stocks.

Four Russell 3,000 stocks are up more than 100% in 2018 already, and they’re all biotech names — CASC, ATRA, IOVA, and FATE. The top performing non-Health Care stocks are Fossil Group (FOSL), Virtu Financial (VIRT), and Eastmak Kodak (KODK). We doubt many investors would have guessed FOSL and KODK to be top performers at the start of the year.

Below is a list of the top performing S&P 500 stocks year-to-date.Netflix (NFLX) is up the most at +69%, followed by XL Group (XL), CSRA, Hewlett Packard Enterprise (HPE), and Amazon.com (AMZN). Other notable winners include NVIDIA (NVDA), Kohl’s (KSS), Under Armour (UAA), salesforce.com (CRM), Adobe (ADBE), and Macy’s (M).