Another question that is common relates to processed meat products. Once a processed meat product (ham, hot dog, lunchmeat, etc.) package is opened, the product should be good for up to seven days unless another type of date is on the package and has passed. After the seven days, the product should not be consumed.
Primary research is any type of research that you go out and collect yourself. Examples include surveys, interviews, observations, and ethnographic research. A good researcher knows how to use both primary and secondary sources in her writing and to integrate them in a cohesive fashion.
Primary sources are written by the scientists that performed the experiment and are writing about it. They are normally found in peer-reviewed journals. Your example is of a primary source. Primary sources can cite other articles, but must be based on novel research. Secondary sources are commonly found in general magazines and newspapers in the science sections. They cite original research, and contribute nothing new or original to the report.