Interactive Brokers vs. Open Tick - volume data

C

chvid

Hi there.

What accounts for the difference in volume data between Interactive Brokers and Open Tick?

For example for Apple I get:

Interactive brokers:

2008-04-09 09:00 152.05 50448.0
2008-04-09 10:00 152.75 56523.0
2008-04-09 11:00 150.74 39637.0
2008-04-09 12:00 150.85 31612.0

Open Tick:

2008-04-09 09:00 152.05 2050622.0
2008-04-09 10:00 152.75 2348828.0
2008-04-09 11:00 150.74 1617529.0
2008-04-09 12:00 150.85 1262443.0

(When I ask for hourly bar data).

Interactive brokers seem to return volume in lots of 100 shares.

The volume data corresponds to what I get from Google summerised over a full day (minus 2-3%).

Open Tick however seems to be around 50% off.

Does anyone know what causes this difference?
 

Attachments

OpenTick separates its data by exchange. What is apparently happening when you request historical data is that you are just getting the data for the first exchange that had a tick. See http://www.opentick.com/dokuwiki/doku.php?id=general:exchange_codes.

You can use @ for the exchange code when collecting live data to request data from all exchanges, but with historical data the only option is apparently to download data from all the applicable exchanges and aggregate it.
 
Thanks dsplaisted - so the Open Tick data is not wrong - it just does not have data from all of Nasdaq?

If I summerise over a full day - i.e. 2008-04-08 (see the attached xls-file for the actual data) - I get:

36,224,800

From Google Finance (http://finance.google.com/finance/historical?q=NASDAQ:AAPL).

This from IB:

353,454

And this from Open Tick:

14,100,976

Compared to Google IB is off by a factor of 102.5, Open Tick is off by a factor of 2.57.

(Other days yield similar results.)
 
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