Assessment, Statistics, and Research

  Skewed Distributions* Skewed distributions have one tail that is longer than the other tail compared to the "normal" distribution, which is perfectly symmetrical. Skew affects the location of the central values of the mean and median. Positive Skew Below is an image of positive skew, which is also called right skew. Skew is named for the "tail." If you had statistics, you may have heard a professor say, "the tail tells the tale." The tail is the extended part of the distribution close to the horizontal axis. The large "hump" area to the left represents the location of most data. In behavioural science, the high part often refers to the location of most of the scores. Thus, in positively skewed distributions, most of the participants earned low scores and few obtained high scores as you can see by the low level of the curve, or the tail, to the right. Negative Skew As you might expect, negatively skewed distributions have the long tail on the le...

Can you answer these questions that every counselor ought to know? Choose the BEST available answer. I'll post the answers below. 1. If the correlation between a test of intelligence and a test of achievement is usually between .88 and .92, how well can you use the intelligence test results to predict achievement test results? A. Very well B. Moderately well C. Not well at all D. None of the above 2. A personality test score was high on a scale of Extraversion. The validity of the Extraversion scale was reported as .52 to .57 compared to similar tests. How much confidence should the person have that their score is "valid?" A. A high degree B. A moderate degree C. A low degree D. None of the above 3. School counselors administered a questionnaire to 1,000 students. They calculated results for answers about four school improvements rated on a scale of 1 to 5. Most of the scores were in the range of 18 to 20. The counselors reported a mean rating o...

Averages Can Be Deceiving What You Need to Know About Averages Most people assume that a simple statistic like a mean or a median tells the whole story. It doesn’t. Averages can clarify—but they can also mislead—depending on which one you use and how your data are distributed. Understanding the mean, median, and mode helps you interpret test scores, salaries, evaluations, and research findings with greater accuracy. CALCULATOR : I have included a basic calculator at the bottom of this page. The Mean, Median, and Mode Mean The mean is the arithmetic average of a set of numbers. You calculate it by adding all the values and dividing by the number of values. Example: For the data 1, 2, 3, 4, 5, the sum is 15 and the mean is 3. The mean uses every value in the dataset, which makes it useful but also sensitive to extreme scores. Median The median is the middle value when numbers are arranged from lowest to highest. Half the values fall above it and half fall below it. Example: In the set 1,...