Basic Statistical Concepts
Measures of Central Tendency: Mean, Median, and Mode
Mean: The mean, or average, is a number calculated by adding a series of values and then dividing by the number of values. For example, to find the mean of the numbers 5, 19, and 27, we add them and divide by the number of values (3). The mean would then be 17 (Schaefer and Lamm 1992: 36).
Median: The median is the midpoint or number that divides a series of values (which are ranked in ascending or descending order). For the quiz discussed above, the median is 8 (Schaefer and Lamm 1992: 36).
Rates and Percentages
A percentage is a portion based on 100. Use of percentages allows one to compare groups of different sizes.
Example: Comparing Populations of Different Sizes If we are comparing contributors to a town's Baptist and Roman Catholic churches, the absolute numbers of contributors could be misleading if there were many more Baptists than Catholics living in the town. With percentages, we can obtain a more meaningful comparison, showing the proportion of persons in each group who contribute to their respective churches (Schaefer and Lamm 1992: 36). |
Target Populations and Samples
The target population refers to everyone in a group that is studies. For example, if one wants to know how people will vote in an election, the target population is everyone who is eligible to vote. How can a researcher study a population as large as that of the United States? The answer is that one cannot study entire populations. Large populations are simply too big. The researcher, therefore, needs to look at a small subset of the population. We call this subset a sample. The trick is to make sure that your sample closely parallels the characteristics of the larger population.
Random Sample: Henslin (1999:126) contends that a random sample is one in which everyone in a population has the same chance of being included in a study. A random sample is necessary if one is going to attempt to generalize the findings in a study to the larger population.