Hi Brian,
I think there may be an issue with the split-table adjustments in the daily price data. My backtest suddenly showed a large drawdown in the 2015 date range, which appears to be related to split adjustments downloaded within the last couple of days.
The split records I checked from 2015 onward are stored with ratio = 1.000 (no adjustment), including the examples below:
| Stock | Split date | Raw close before → after | Ratio in split table | Expected ratio |
|---|---|---|---|---|
| GILD | 2013-01-28 | 79.36 → 39.44 | 0.500 ✓ | 0.5 |
| AAPL | 2014-06-09 | 645.57 → 93.70 | 0.143 ✓ | 1/7 |
| CNC | 2015-02-20 | 120.67 → 59.85 | 1.000 ✗ | 0.5 |
| MPC | 2015-06-11 | 101.79 → 52.03 | 1.000 ✗ | 0.5 |
| NFLX | 2015-07-15 | 702.60 → 98.13 | 1.000 ✗ | 1/7 |
| SKX | 2015-10-16 | 132.67 → 45.15 | 1.000 ✗ | 1/3 |
| GPN | 2015-11-03 | 136.23 → 67.56 | 1.000 ✗ | 0.5 |
| HRL | 2016-02-10 | 82.86 → 41.67 | 1.000 ✗ | 0.5 |
| AAPL / TSLA | 2020-08-31 | 499 → 129 / 2213 → 498 | 1.000 ✗ | 1/4, 1/5 |
| NVDA | 2021-07-20 | 751 → 186 | 1.000 ✗ | 1/4 |
| WMT | 2024-02-26 | 175.56 → 59.60 | 1.000 ✗ | 1/3 |
| NVDA | 2024-06-10 | 1208.88 → 121.79 | 1.000 ✗ | 1/10 |
| ORLY | 2025-06-10 | 1348.10 → 91.71 | 1.000 ✗ | 1/15 |
Across the full table, the percentage of records stored with a ratio of 1.0 increases sharply starting in 2015. This affects both splits and dividends:
| Years | Splits stored with ratio 1.0 (no adjustment) | Dividends stored with ratio 1.0 |
|---|---|---|
| 2007–2014 | 4–9% | 1–3% |
| 2015–2026 | 83–95% | 85–99% |
Could you please check whether a recent data update may have caused this, and advise on how to correct the affected adjustment records?
Thanks,
Kamran