I need to calculate the put-call ratio for an American option. But I'm a complete naïf: I don't know how. I think I'd use the put open interest and the call open interest. I can imagine two ways to calculate PCR:
Simply (as some references tell me) take OIputs divided by OIcalls and there's my number, right there:
PCR = OIputs / OIcalls
Or (as other sources seem to suggest) take OIputs divided by the sum of OIputs and OIcalls:
PCR = OIputs / ( OIputs + OIcalls )
Further, I don't even know if the ratio can most usefully be expressed as a decimal (i.e., 0.667) or as a fraction (i.e., 2/3) or as the ratio notation I learned in grammar school (i.e., 2:3).
What's the usual, expected, and/or "right" way to calculate PCR?