revenues from our DVD-by-mail membership services. The price per plan for DVD-by-mail varies from $4.99 to $43.99 per month according to the plan chosen by the member. DVD-by-mail plans differ by the number of DVDs that a member may have out at any given point. Members electing access to high definition Blu-ray discs, in addition to standard definition DVDs, pay a surcharge ranging from $2 to $4 per month for our most popular plans.

The decrease in our domestic DVD revenues was due to a 16% decrease in the average number of paid memberships.

The decrease in domestic DVD cost of revenues was primarily due to a $16.0 million decrease in content expenses and a $43.0 million decrease in delivery expenses resulting from a 22% decrease in the number of DVDs mailed to members. The decrease in shipments was driven by a decline in the number of DVD memberships coupled with a decrease in usage by these members. Other costs, primarily those associated with processing and customer service expenses, decreased $15.6 million primarily due to a decrease in hub operation expenses resulting from the decline in DVD shipments.

Our Domestic DVD segment had a contribution margin of 48% for the year ended December 31, 2014, and was flat as compared to the year ended December 31, 2013.

The decrease in our domestic DVD revenues was due to a 20% decrease in the average number of paid memberships.

The decrease in domestic DVD cost of revenues was primarily due to a $62.0 million decrease in content expenses and a $44.2 million decrease in delivery expenses resulting from a 19% decrease in the number of DVDs mailed to members. The decrease in shipments was driven by a decline in the number of DVD memberships. Other costs, primarily those associated with content processing and customer service center expenses, decreased $20.4 million primarily due to a decrease in hub operation expenses resulting from the decline in DVD shipments.

Our Domestic DVD segment had a contribution margin of 48% for the year ended December 31, 2013, and was relatively flat as compared to the year ended December 31, 2012.

Consolidated Operating Expenses

Technology and Development

Technology and development expenses consist of payroll and related costs incurred in making improvements to our service offerings, including testing, maintaining and modifying our user interface, our recommendation, merchandising and streaming delivery technology, as well as our telecommunications systems and infrastructures. Technology and development expenses also include costs associated with computer hardware and software.

The increase in technology and development expenses was primarily due to an $87.4 million increase in personnel-related costs, including stock-based compensation expense, resulting from an increase in compensation for existing employees and a 12% growth in average headcount supporting continued improvements in our streaming service and our international expansion.

Technology and development

The increase in technology and development expenses was primarily the result of a $42.8 million increase in personnel-related costs. These increases are primarily due to increases in employee