Quote from thinkplus:
DD are little more delta and vega neutral and have higher theta than DC. it depends on your outlook of IV to say if it is good or not. If you expect Iv to go up, DC are better and vice versa.
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Quote from FT79:
Not true
I wish you gave an explanation rather than an opinion. Anyway, here is an explanation / example / reasoning behind the statement. I have taken the data from Russell 2000 (RUT) options closing prices today.
RUT @753.37 15-Aug-08
DD
--
Sell Sep 770 C, -40 Delta, 30 Theta, -90 Vega
Buy Oct 780 C, 39 Delta, -23 Theta, 120 Vega
Sell Sep 740 P, 38 Delta, 29 Theta, -89 Vega
Buy Oct 730 P, -35 Delta, -22 Theta, 116 Vega
Total: 2 Delta, 14 Theta, 57 Vega
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DC (strikes 25 pts. from the underlying)
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Sell Sep 780 C, -33 Delta, 28 Theta, -84 Vega
Buy Oct 780 C, 39 Delta, -23 Theta, 120 Vega
Sell Sep 730 P, 32 Delta, 28 Theta, -83 Vega
Buy Oct 730 P, -35 Delta, -22 Theta, 116 Vega
Total: 3 Delta, 11 Theta, 69 Vega
=================================================
DC (strikes 15 pts. from the underlying)
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Sell Sep 770 C, -40 Delta, 30 Theta, -90 Vega
Buy Oct 770 C, 44 Delta, -24 Theta, 124 Vega
Sell Sep 740 P, 38 Delta, 29 Theta, -89 Vega
Buy Oct 740 P, -40 Delta, -23 Theta, 121 Vega
Total: 3 Delta, 12 Theta, 66 Vega
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As you can see the DD delta and vega are less and theta is higher than DC. (note: I have rounded the decimals).