Statistics and Probability

Data Collection and Sampling

• **Primary Data**: Data collected directly by the researcher.
• **Secondary Data**: Data collected by others, e.g. government statistics.
• **Population**: The complete set of all items/individuals of interest.
• **Sample**: A subset of the population, selected to represent the whole.
• **Random Sampling**: Each member of the population has an equal chance of being selected.
• **Stratified Sampling**: The population is divided into groups, and samples are taken from each group.
• **Systematic Sampling**: Every nth item in the population is selected, starting from a random point.
• **Bias**: A systematic error in sampling or data collection that skews the results.
• **Pilot Study**: A small-scale preliminary study to test the methods and procedures.