Generalization is an act of reasoning that involves drawing broad inferences from particular observations in quantitative research, but is more controversial in qualitative research. The goal of most qualitative studies is not to generalize but rather to provide a rich, contextualized understanding of some aspect of human experience through the intensive study of particular cases. The four types of quantitative research are Survey (Descriptive), Correlational, Causal comparative (Ex post facto) and Experimental. Experimental research involves a hypothesis, a variable that can be manipulated by the researcher, and variables that can be measured, calculated and compared in a controlled environment. Causal comparative research seeks to find relationships between independent and dependent variables after an action or event has already occurred. Descriptive research describes situations; it does not make accurate predictions, nor does it determine cause and effect. Historical research is a qualitative research that examines past events to draw conclusions and make predictions about the future.