Learn the distinctions between simple and stratified random sampling. Understand how researchers use these methods to accurately represent data populations.

National security, unlocked. Each Thursday, host Mary Louise Kelly and a team of NPR correspondents discuss the biggest national security news of the week. With decades of reporting from battlefields ...

Optical techniques are methods that use light to probe or control matter. One prominent example is optical spectroscopy, which includes such methods as pump–probe spectroscopy, Raman spectroscopy and ...

Characterization and analytical techniques are methods used to identify, isolate or quantify chemicals or materials, or to characterize their physical properties. They include microscopy, light or ...