term for a case-control study. This use of the term "retrospective study" is misleading, however, and should be avoided because other research designs besides case-control studies are also retrospective in orientation. Superiority trials are designed to demonstrate that one treatment is more effective than a given reference treatment. This type of study design is often used to test the effectiveness of a treatment compared to placebo or to the currently best available treatment. Non-inferiority trials are designed to demonstrate that a treatment is at least not appreciably less effective than a given reference treatment. This type of study design is often employed when comparing a new treatment to an established medical standard of care, in situations where the new treatment is cheaper, safer or more convenient than the reference treatment and would therefore be preferable if not appreciably less effective. Equivalence trials are designed to demonstrate that two treatments are equally effective. When using "parallel groups", each patient receives one treatment; in a "crossover study", each patient receives several treatments but in different order. A longitudinal study assesses research subjects over two or more points in time; by contrast, a cross-sectional study assesses research subjects at only one point in time (so case-control, cohort, and randomized studies are not cross-sectional). See also Conceptual framework Epidemiological methods Epidemiology Experimental control Meta-analysis Operationalization Academic clinical trials Design of experiments Research design References External links Some aspects of study design Tufts University web site Comparison of strength Description of study designs from the National Cancer Institute Medical statistics Design of experiments Scientific method de:Forschungsdesign