Blocks are assigned either automatically or manually, depending on whether you use dynamic or static randomization.

• With dynamic assignment, Clinical One Cloud Service assigns a block to a given site, country, or region during randomization.

  We recommend using dynamic assignment. This type of randomization uses the numbers in the list more efficiently and can help reduce having large sections of unassigned numbers.

  For instance, for site-blocked randomization, Clinical One Cloud Service assigns the first block to the first site that enrolls a subject. Subsequent subjects who enroll at the site are randomized using the numbers in that block until all numbers are used. Clinical One Cloud Service assigns another block to the site after all numbers are used and another subject enrolls.

• With static assignment, a statistician assigns blocks to sites, countries, or regions in the randomization list.

  Static assignment can sometimes lead to randomization failures that are difficult to troubleshoot.