In the current session, Illumina Inc. ILMN is trading at $419.95, after a 9.21% spike. Over the past month, the stock increased by 4.76%, and in the past year, by 49.45%. With performance like this, long-term shareholders optimistic but others are more likely to look into the price-to-earnings ratio to see if the stock might be overvalued.

Assuming that all other factors are held constant, this could present itself as an opportunity for shareholders trying to capitalize on the higher share price. The stock is currently under from its 52 week high by 24.44%.

The P/E ratio is used by long-term shareholders to assess the company's market performance against aggregate market data, historical earnings, and the industry at large. A lower P/E indicates that shareholders do not expect the stock to perform better in the future, and that the company is probably undervalued. It shows that shareholders are less than willing to pay a high share price, because they do not expect the company to exhibit growth, in terms of future earnings.

Most often, an industry will prevail in a particular phase of a business cycle, than other industries.

Compared to the aggregate P/E ratio of the 133.62 in the Life Sciences Tools & Services industry, Illumina Inc. has a lower P/E ratio of 86.41. Shareholders might be inclined to think that the stock might perform worse than its industry peers. It's also possible that the stock is undervalued.

Price to earnings ratio is not always a great indicator of the company's performance. Depending on the earnings makeup of a company, investors can become unable to attain key insights from trailing earnings.