Prospective vs. retrospective studies
Case-Control studies are usually but not exclusively retrospective, the opposite is true for cohort studies.
http://www.statsdirect.com/help/basics/prospective.htm

Ensaio Clínico Cruzado (Crossover) http://tinyurl.com/mmc2n2
Crossover study: A crossover study (also referred to as a crossover trial) is a longitudinal study in which subjects receive a sequence of different treatments (or exposures). While crossover studies can be observational studies, many important crossover studies are controlled experiments, which are discussed in this article. http://en.wikipedia.org/wiki/Crossover_study

An unblinded, ****prospective, case-control, crossover study*** comparing bedside addition of fluid thickener to pre-thickened fluids was performed on 11 dysphagic extended care residents for a period of 12 weeks. Constipation rates, fluid, protein, calorie, calcium and vitamin C intakes were determined at baseline and weeks 6 and 12.
http://ageing.oxfordjournals.org/cgi/reprint/35/suppl_3/i31....