Why Industry P/E Series Differ: Averaging Stock-Level P/E Ratios
Summary
The document asks why a historical price-to-earnings series for China’s pharmaceutical industry differs from a series calculated in code. The example selects constituents classified under the 2021 Shenwan industry scheme, joins them to daily stock valuation data, and takes the arithmetic mean of constituent trailing P/E ratios for each date. It compares this approach with an external industry chart but provides no chart values or resolution to the question.
The example highlights that an industry valuation series depends on its construction. Averaging stock-level P/E ratios may differ from an aggregate industry P/E calculated from total market capitalization and earnings; treatment of loss-making firms, constituent changes, and missing observations can also affect results. The document does not establish which method the external chart uses, so it cannot identify the cause of the discrepancy. Researchers should confirm definitions and filters before comparing series.
Key ideas
- A daily arithmetic mean of constituent P/E ratios is one way to construct an industry valuation series.
- An external industry P/E series may use a different aggregation method or constituent definition.
- Loss-making firms, membership changes, and missing data can influence the calculated average.
- The example raises the discrepancy but does not provide enough evidence to resolve it.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.