I often approximate DV01 using: DV01 = Market value of position * 1bps * Duration in years.
Here, for Bond or CDS, I generally assume duration = residual maturity.
Assume I buy a bond. So my position's market value will be +ve and hence DV01 by above method will be +ve. Now, a Long Bond position gives +ve dv01 only if yield decreases by 1bps.
Hence I feel that in this approximation, there is an implicit assumption that dv01 is being calculated for 1bps decrease in yield. And this assumption is irrespective of the type of product (bond, cds, IRS etc.) for which dv01 is calculated.
Am I correct in thinking so?