What type of contract has gained popularity by transferring responsibility for productivity to the contractor?

Unit price contracts have gained popularity because they allow for the contractor to be compensated based on the quantity of work performed rather than a pre-determined total price. This type of contract effectively transfers the responsibility for productivity from the client to the contractor. The contractor is incentivized to work efficiently, as their earnings are directly linked to the volume of work completed. This approach can lead to better cost management for clients as they pay for actual work done rather than potentially overspending on fixed estimates that may not reflect the final effort required.

In contrast, fixed price contracts represent a set price for a specific job or project, which does not account for productivity variations and can lead to disputes if actual work exceeds initial expectations. Time and materials contracts pay for the time spent and materials used, but they can lead to unpredictability in costs and do not incentivize the contractor to maximize productivity. Retainer agreements typically involve continuous services over a period, focusing on access to support rather than productivity output linked to tasks completed.