No. of Recommendations: 1
2) Use Yahoo!'s unadjusted prices and split/dividend info to do our own adjustments (can't be that hard, as long as the data is good)

I did that last month for my add-in.

1) Wait for Yahoo! to fix their adjusted prices (may happen, you never know)

They added dividend adjustments last Friday, so I had to remove the adjustment processing in my add-in.

However, the adjustments by Yahoo are done incorrectly for anything other than daily data. For example, someone pointed out my add-in was returning data different from what Google has. At first, I said it was because Google didn't adjust for dividends. Which was correct. However, on their monthly data, if a stock pays out a dividend during the month, they adjust the month-end price for the dividend paid earlier in the month. Not right.

I've looked for a cookbook algorithm for adjusting close prices but haven't found one.

Easy. The CRSP standard. In the add-in, I simply did:

Cumulative adjustment = Cumulative adjustment * (Previous Close - Dividend Amount) / Previous Close

The adjustment needs to be made each time a dividend is paid out, and then the cumulative adjustment is applied to all historical data.

For example:

   Date       Open    High     Low   Close Volume    Unadj  Div Adj Split Adj Dividend
2017-06-13 $207.58 $209.67 $207.56 $209.11 1684900 $209.11 1.000000 1.000000
2017-06-12 $206.93 $208.42 $205.50 $207.39 2388200 $207.39 1.000000 1.000000
2017-06-09 $206.00 $206.97 $205.64 $206.93 1893100 $206.93 1.000000 1.000000
2017-06-08 $205.01 $206.03 $204.09 $205.94 2441400 $205.94 1.000000 1.000000
2017-06-07 $205.73 $205.87 $204.10 $205.01 1885600 $205.01 1.000000 1.000000
2017-06-06 $206.01 $206.66 $205.41 $205.41 1458800 $205.41 1.000000 1.000000
2017-06-05 $206.77 $207.33 $206.22 $206.22 1253100 $206.22 1.000000 1.000000
2017-06-02 $205.06 $207.39 $204.79 $206.70 1831900 $206.70 1.000000 1.000000
2017-06-01 $204.25 $204.90 $203.68 $204.35 2352700 $204.35 1.000000 1.000000
2017-05-31 $202.73 $204.47 $202.27 $204.47 3096800 $204.47 1.000000 1.000000
2017-05-30 $200.31 $203.03 $199.96 $202.44 2171100 $202.44 1.000000 1.000000
2017-05-26 $199.14 $200.69 $198.97 $200.67 1410600 $200.67 1.000000 1.000000
2017-05-25 $198.41 $199.61 $197.75 $199.54 1508000 $199.54 1.000000 1.000000
2017-05-24 $198.49 $198.53 $197.28 $197.49 1206400 $197.49 1.000000 1.000000
2017-05-23 $198.73 $198.97 $197.52 $197.73 1514200 $197.73 1.000000 1.000000
2017-05-22 $196.35 $198.67 $196.35 $198.51 1835900 $198.51 1.000000 1.000000
2017-05-19 $196.30 $196.30 $194.45 $195.80 1894700 $195.80 1.000000 1.000000
2017-05-18 $194.50 $195.82 $193.54 $195.24 1929000 $195.24 1.000000 1.000000
2017-05-17 $196.74 $196.74 $194.72 $194.84 1881800 $194.84 1.000000 1.000000 $1.18
2017-05-16 $196.31 $196.76 $195.69 $196.74 1183600 $197.91 0.994027 1.000000
2017-05-15 $195.50 $196.57 $195.06 $196.46 1474500 $197.63 0.994027 1.000000
2017-05-12 $194.74 $195.95 $194.70 $195.40 1323100 $196.57 0.994027 1.000000
2017-05-11 $194.88 $195.77 $194.10 $195.58 1705000 $196.75 0.994027 1.000000
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