The description of a sample implies that a researcher defines variables, measures them, and for each measure calculates one or more of the following descriptive statistics: measures of central tendency and measures of variability. Measures of central tendency are: mean, median and mode. Measures of variability are: standard deviation, variance and range. The researcher can also calculate the derived scores which help interpreting the sample's scores on the variables that were measured. Derived scores aid the interpretation by providing a quantitative measure of each individual's performance relative to a comparison group. Age equivalents, grade equivalents, percentiles, and standard scores are examples of derived scores commonly used in descriptive research.
Some descriptive research provide statistical information about aspects of education that interest policy makers and educators. This type of research is the specialty of the National Center for Education Statistics. Many of this center's research results are published in an annual volume called the Digest of Educational Statistics. This center also administers the National Assessment of Educational Progress (NAEP), which is a collection of descriptive information about the performance of youth in the different subjects taught in public schools. A noticeable NAEP publication is the Reading Report Card, which reports descriptive statistics about student's performance in reading at different levels. At a higher level the International Association for the the Evaluation of Educational Achievement (IEA) does descriptive studies of the academic achievement of students in many nations including the United States.
The two main types of descriptive research differ by the time the variables are measured. In the first type the variables or the characteristics of a sample are measured at one point in time. In the second type which is called longitudinal a sample is followed over time.
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