When there's a 2-for-1 stock split,
- the number of shares doubles, while
- the value of the stock halves
For symbol 2154 on the Tokyo Stock Exchange, there was such a 2-for-1 split on 2016/3/29.
However when looking at csv data download from Yahoo, I see the "adjusted close" doubling (not halving), while the unadjusted "Close", as well as Open, High, Low, barely move.
Here's an excerpt:
2154 Open High Low Close Volume Adj Close
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2016-03-30 1576.00 1602.00 1530.00 1530.00 63600 1503.08
2016-03-29 1455.00 1620.00 1455.00 1551.00 86700 1523.71
2016-03-28 1450.00 1452.50 1425.50 1450.00 29000 712.24
2016-03-25 1469.50 1475.00 1438.50 1442.50 23200 708.56
How does this all add up? What was the actual price used on 2016/03/28 when 2154 was traded? Somewhere around 1450? Or 700? Or 2900?
I just looked at another set of Yahoo data for 2170 on the Tokyo Stock Exchange, which had a 100-for-1 split on 2014/3/27, and here everything looks as I would have expected.
2170 Open High Low Close Volume Adj Close
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2014-03-28 230.00 230.00 219.00 230.00 74700 190.4468
2014-03-27 224.00 229.00 191.00 225.00 119300 186.3067
2014-03-26 23500.00 23500.00 22000.00 22339.9994 181700 184.2366
2014-03-25 23739.9994 24080.0003 22810.0006 23230.0003 278800 191.5764
Is Yahoo's data for 2154 just wrong? Did they perhaps get already adjusted OHLC data for 2154, used those values as their OHLC values, and then re-adjusted the already adjusted close, which lead to incorrect "Adj Close" values?
That would also mean that the actual share price of symbol 2154 on 2016/3/28 would have been around 2900.