Those that fall into the "unknown effectiveness" category are medical treatments that "for which there are currently insufficient data or data of inadequate quality."
When health policy wonks talk about ending unnecessary care, they usually mean targeting these types of treatments -- the ones where we have no idea whether they're making us any healthier. but still increase spending.
There are specific bodies dedicated to figuring out whether these 1,500 treatments actually work. That includes the Patient Centered Outcomes Research Institute, or PCORI, which was created by the health-care law to study comparative effectiveness research. They have been giving out grants to researchers to figure whether screening adolescent lipid levels will help control cholesterol and whether it's better to treat serious bacterial infections with oral or intravenous antibiotics.
This Clinical Evidence research suggests they'll have no shortage of medical treatments to study.