ABSTRACT
This chapter presents and describes some more advanced concepts and techniques that are commonly used in quantitative analysis of environmental issues. It begins to understand the concept of validity: how it is defined in quantitative research and why it is important. The internal validity of a conclusion can be threatened by not accounting for other factors that may be causing the estimated relationship among research people's variables. In quantitative research, external validity is about whether research people's conclusions, based upon the observations in their sample, are true for the larger population from which they drew the sample. The chapter explains sample selection bias with a simple example. It focuses on how to characterize the relationship among variables. Creating a scatterplot or calculating a correlation coefficient can be suggestive of a positive, negative, or zero relationship between two variables. The confidence interval provides a measure of the reliability of an estimate of the relationship among variables.
