Understanding and Applying Research Design

STATISTICAL PROCEDURES UNIT B: THE NATURE OF INFERENTIAL STATISTICS¹

Descriptive statistics examine the ways a set of scores or observations can be characterized. Is the set of scores normally distributed? What is the most characteristic indicator of central tendency? Are there extreme scores? What information about the nature of the scores can be obtained from examining histograms and other graphs?

Thus far, we have examined raw score distributions made up of individual raw score values. For example, a set of 40 schools each had percentages of students qualified for FR, or percentages of students passing math and reading achievement scores. We tried to understand the nature of these variables; whether they were normally distributed and how the percentages were distributed compared to the standard normal distribution.

In the real world of research and statistics, practitioners almost always deal with sample values, since they very rarely have access to population information. Thus, for example, we might want to understand whether the job satisfaction ratings of a sample of 100 software engineers is characteristic of all software engineers, not just our 100. Since it is practically impossible to get job satisfaction ratings for all software engineers, we must measure the extent to which sample values approximate or estimate the overall population values. We are using the picture at hand (of our sample group) to get a better picture of the overall (population) group that we have ...