Written cases, pioneered by Monitor Deloitte, and now used by all firms are very intimidating. Written cases actually test core prioritization skills much better than verbal cases, since written case interviews can dump tonnes of data on a candidate. The trick to written cases is to have a filtering system to find the data you need from the worthless data, and of course, recognizing that not all the data is useful. Written cases mirror cases done in case-method schools like Harvard. Lots of data is provided in those cases, but not all is useful. Your job is to find the useful data and that means having a framework upfront.