CJ490 Non-Probability Sampling 1

Introduction According to Bachman & Schutt (2007), when collecting a sample using nonprobability sampling technique, elements within the population do not have a probability of being selected into the sample. We cannot be sure the selected sample actually represents the population. 2

Population & Sample Population: All the elements in which we are interested for example- cities, states, countries, schools, jails, and prisons. Sample: A subset of a larger population –i.e. Prison- only death row inmates. 3

Importance of Sampling Is whether it’s truly a representative of the population from which it was selected and whether the sample are based on probability or nonprobability sampling method (p. 110). 4

Non-Probability Sampling Is a sampling methods in which the probability of selection of the population elements is unknown (Bachman & Schutt, 2007). 5

4 Non-Probability Sampling Methods Availability: It a convenience sample. Quota: A portion/% of the sample. Purposive/Judgment: Researcher uses own judgment in selection such as randomly. Snowball: ID one person-ask that person to ID others and speak to him/her and continue---- (p. 126). 6

Strength & Weaknesses Least expensive. Least time-consuming. Most convenient. Selection bias. Sample not representative. Not recommended for descriptive or causal research (Creswell, 2002). 7

Strength & Weaknesses Low cost. Not time consuming. Useful for some types of forecasting. Does not allow generalization. Subjective, may make the sample unrepresentative (Creswell, 2002). 8

Strength & Weaknesses 9 Sample can be controlled for certain characteristics. Selection bias. No assurance of representativeness. Projecting data beyond sample inappropriate. Can estimate rare characteristics. Time consuming. Projecting data beyond sample inappropriate (Creswell, 2002).

References Bachman, R. & Schutt, R. K., (2007). The Practice of Research in Criminology and Criminal Justice (3 rd ed.) Sage. Creswell, J. W. (2002). Educational Research: Planning, Conducting, and Evaluating Quantitative and Qualitative Research: Merrill Prentice Hall. 10