# Criminal Justice

### Probability Versus Nonprobability Sampling

#### Competencies Addressed in This Discussion

• Competency 1: Differentiate research methods used by criminal justice agencies.

#### Introduction

Probability sampling is used to assist researchers in generalizing from observed cases to unobserved cases. As a research method, probability sampling is a method of selection in which each member of a population has a known chance or probability of being selected. If it is the case that all members of a population are similar in all respects, there is no need for sampling procedures. A sample must contain essentially the same variations that exist in the population. The original sampling method must be known to evaluate the quality of a sample and findings based on that sample’s responses and behavior, and findings will only be as generalizable as the sample is to the original larger target population.

The purpose of this discussion is to understand that there are various methods of sampling and that a successful study relies on the thoughtful sample planning to choose the best research method to effectively investigate social processes without having to consider every setting or person. Based on your reading assignment and any additional research needed, address the following in your main post:

1. Explain, using examples, how sampling as a research method is used for statistical data analysis in criminology or criminal justice.
2. Differentiate between the advantages and disadvantages of probability-based sampling designs and nonprobability-based designs.
3. Explore whether any of the research described in Chapter 5 of your Fundamentals of Research in Criminology and Criminal Justice text with a nonprobability-based design has been conducted instead with the probability-based design.

### Probability Samples and Validity of Generalizations

#### Competencies Addressed in This Discussion

• Competency 2: Articulate a problem statement appropriate for examination using criminal justice research methods.
• Competency 4: Use a common research method of criminal justice practitioners to examine the problem statement.

#### Introduction

Various sampling designs are available to suit different research and purposes populations. For example, although simple random sampling is logically the most fundamental probability sampling technique, it is not often in practice. Systematic sampling employs a sampling frame for selection of units that appear at a certain specified interval. This research method is, however, the functional equivalent to the simple random sampling method. The stratification method is valuable because it improves how representative a sample is by reducing the sampling error. When selecting adequate numbers of certain types of subjects who are relatively rare in the population being studied, disproportionate stratified sampling can be particularly useful. Finally, the method of multistage cluster sampling is most often utilized when there exists no list of the members of an entire population.

In Chapter 5 of Fundamentals of Research in Criminology and Criminal Justice, you learned about the three main types of probability sampling. Using your library research skills and what you have learned about sampling methods, research scholarly journal articles to find one that describes criminological research using a sample drawn from some population and respond to the following in your main post:

1. Describe the type of probability sample used in the study.
2. Draft a problem statement for a research topic relevant to criminology that could be used in conjunction with the probability sampling method you shared.
3. Differentiate the strong and weak points in how the sample was drawn in terms of how they may affect the success of the study.
4. Analyze your level of confidence in the validity of generalizations about the population based on the sample.