A PWS is a SOW for Performance-Based Acquisitions (PBA). PBAs are structured around the desired results/objectives, as opposed to the "how". In other words, the Government doesn't (or at least shouldn't in PBA) attempt to tell the KTR the step-by-step guidance on how to meet the objectives - it leaves the approach up to the KTR - after all, they are the SME most of the time.
In the PBA world, and within the services arena, agencies have a choice to deploy either a SOO or a PWS to industry. When you read FAR Part 37, and what is included in each, there are naturally some differences. One of the differences is that a PWS includes performance standards - in other words, "to what level" the Government's performance objectives/desired results must be met. A SOO includes the performance objectives/desired results, but does not include these performance standards. Instead, the KTR would propose performance standards that it feels are comensurate with the nature of the requirement - risk and other factors considered. They do this by submitting a PWS as part of their proposal. Now, FAR 37.601( states that Performance-based contracts for services "shall" (the imperative) include a PWS. However, the PWS is not the "how" the KTR intends to meet the objectives and standards specified in the PWS. By sheer definition of PWS and PBA in FAR 2.101, a PWS should never include the "how".
Some PCO's want to know the "how" as well though. I've seen it as a separate volume requirement. They want to evaluate it. They want to attach it to Section J and then (here it gets tricky) enforce it once the contract gets awarded.
They feel that if they made an award decision based upon the best value continuum - namely trade-offs - and they award a contract to a KTR based upon (among other factors) that KTR's "how", then that award decision is invalidated if the KTR possesses the agility to freelance after the award is distributed. That said, if we stick to the spirit of PBA after the award is made, then the Government shouldn't focus on the how - only on if the true objectives and performance standards of the contract are being met. Because if the Government has done a good job up front in identifying the true objectives, then, as long as they are being met at the standards identified, it shouldn't matter the approach the KTR is taking.
I've seen the Government manage what is called a FFP as if it were a LH contract - simply because the contractor proposed an approach that included a certain amount of people/labor cats....and now the Government is holding them to it, but still calling it a FFP PBA.
I think I may be muddying the waters though.....sorry, I'm new to the blog...(smile)