Investopedia

Simple Random Sampling: 6 Basic Steps With Examples

Adam Hayes, Ph.D., CFA, is a financial writer with 15+ years Wall Street experience as a derivatives trader. Besides his extensive derivative trading expertise, Adam is an expert in economics and ...
Investopedia

How Stratified Random Sampling Works, With Examples

Adam Hayes, Ph.D., CFA, is a financial writer with 15+ years Wall Street experience as a derivatives trader. Besides his extensive derivative trading expertise, Adam is an expert in economics and ...
BBC

Introduction to fieldwork - Eduqas

primary - information that is collected first-hand, eg tallies, measurements and photographs secondary - information that someone else has previously collected and made available, eg on the internet ...