To check whether a historical price series reflects a stock split, compare the split record with unadjusted prices on either side of the event. Convert the stated ratio to new shares per old share, confirm the effective date, and divide the last pre-split close by that factor. The result should be on roughly the same per-share scale as the first post-split close—but ordinary market movement means the prices need not match exactly.
What a split should change—and what it should not
A stock split changes the number of shares into which a company’s equity is divided and changes the per-share price scale in the opposite direction. In an ordinary split, the split itself does not change the company’s market capitalization. CRSP describes the event as having “no impact on the company’s market capitalization.” That is a statement about the mechanical effect of the split, not a claim that the stock’s market value or an investor’s return cannot move for other reasons.
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A split factor is therefore a way to reconcile share units and price scales, not a measure of investment performance. A retrospective adjustment also is not the price at which a share actually traded on a past date.
Gather the right security, dates, and fields
Before doing arithmetic, make sure the records refer to the same security and cover the relevant sessions. A ticker can change over time, so use a durable identifier and historical identity information where available rather than assuming the ticker always identifies one security.
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Obtain daily unadjusted open, high, low, close, and volume (OHLCV) data, plus a corporate-action record for the same security and date range. Nasdaq Data Link documents split events in its Sharadar ACTIONS table and daily price fields in its SEP table. Its documentation distinguishes unadjusted prices from split-adjusted prices and a close adjusted for splits, dividends, and spinoffs; these fields are not interchangeable. See the Nasdaq Data Link Sharadar Equity Prices documentation.
Write down the provider, exact price field, event date convention, and adjustment scope. “Historical close” alone does not tell you whether the number is raw, split-adjusted, or adjusted for additional distributions.
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Check the split factor against raw closes
- Read the event ratio and its convention. Express the ratio as new shares divided by old shares. If the record gives the inverse, convert it. Nasdaq Data Link’s documented 3-for-2 example uses new float divided by old float, giving a factor of 1.5.
- Confirm the effective date. Identify the last trading session before the event and the first session on or after it under the provider’s convention. CRSP says its split events are applied on the Ex-Distribution Date; a different date assumption can make a correct factor appear misplaced.
- Use unadjusted closes on both sides. Divide the last pre-event raw close by the factor:
post-event scale ≈ pre-event raw close / (new shares / old shares). - Compare scales, not exact prices. Check whether the calculated pre-event value is plausibly near the first post-event raw close. A split does not freeze the market price between adjacent sessions, so a difference is normal and this check is not a return calculation.
For example, a 3-for-2 split means r = 3 / 2 = 1.5. If the last pre-event raw close is $150, dividing by 1.5 gives a reference scale of $100 per post-split share. The first post-event close could be higher or lower because the market moved; the arithmetic only tests whether the share-unit conversion is plausible.
Distinguish raw prices from adjusted history
Vendors may publish multiple versions of a price series. In Nasdaq Data Link’s documentation, the unadjusted close includes no corporate-action adjustment; OHLC and volume are adjusted for stock splits and stock dividends; and the close-adjusted field also accounts for cash dividends and spinoffs. A split-only comparison should not silently use a field that includes other distributions.
CRSP describes historical adjustment using a cumulative factor C(t): adjusted price is raw price divided by the factor, while adjusted shares and volume are raw shares and volume multiplied by it. The adjustment base date anchors the series, and the observation on that base date remains unadjusted. Thus an adjusted historical price is a restated value on a chosen share basis—not an observed transaction price from that date. See CRSP’s Chapter 3: CRSP Calculations.
When a provider supplies cumulative factors, inspect the factor across the event and verify its direction. For a forward split, historical pre-event prices expressed in the post-split share basis are lower by the split factor; corresponding historical share counts and volume are higher by that factor. A factor’s anchor and the intervening events determine the adjusted number, so do not assume two vendors’ adjusted series must match unless their definitions and bases match.
Use shares and volume as consistency checks
Where available, compare adjusted share counts and volume with the factor direction. CRSP’s method multiplies shares and volume by the cumulative factor while dividing price by it. This opposite movement is consistent with representing history on a different share basis.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteVolume is also driven by actual trading activity, however, so it is not expected to equal a simple pre/post transformation across neighboring sessions. Treat it as a directional consistency check, not proof of the split record or an exact arithmetic test.
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Investigate mismatches before calling the data wrong
- Wrong event date: Check whether the provider applies the event on the ex-distribution date and whether you selected the last pre-event and first post-event sessions accordingly.
- Inverse ratio: Verify that the record is new shares per old share, not old shares per new share.
- Different adjustment scope: Confirm whether the selected field includes only splits, also stock dividends, or cash dividends and spinoffs.
- Security identity change: Check ticker changes, reorganizations, and identifier continuity across the period.
- Other price-factor events: Review reverse splits, stock dividends, and other distributions. CRSP’s split-event adjustment framework includes some distributions with price factors, while its shares and volume adjustments apply only to stock splits and stock dividends.
- Missing sessions or history gaps: Check whether trading dates are absent or the security’s history is discontinuous. CRSP documents that adjusted values can be missing when an event is uncertain across a gap in trading history.
- Ordinary market movement: If the factor, date, identity, and field all line up, a non-identical adjacent close does not by itself indicate an error.
What the check can establish
A well-documented comparison can show whether a stated split ratio and event date produce a plausible change in raw per-share price scale, and whether an adjusted series applies the factor in the expected direction. It cannot by itself prove that a vendor’s full history is correct, identify the exact price an investor could have obtained, or calculate investment return. For a reproducible report, state the provider, security identifier, price field, event date basis, ratio convention, and any gap or coverage limitation.
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