Assessment, Statistics, and Research

Understanding the Bell Curve and Standard Deviation The bell curve—also known as the normal curve or normal distribution—has mathematical properties that allow researchers to understand where scores (or data points) fall in relation to one another. In a normal distribution, most scores cluster around the center, with fewer scores appearing as you move toward the extremes. Central Tendency in a Normal Curve In a normal distribution, the three measures of central tendency—mode, median, and mean—all fall at the same central point. This midpoint divides the distribution into two equal halves. Standard Deviation Units On the x‑axis of a normal curve, the mean is placed at zero. Standard deviation units extend outward in both directions from the mean. These units help us understand how far a score is from the average. The height of the curve at any point represents the percentage of scores in that area. A large portion of scores fall close to the mean. In fact, about 68% of all scores lie be...

  The term correlation can refer to a statistic and a type of research.  Understanding correlations is an important building block of many complex ideas in statistics and research methods. My focus in this post is on the common correlation statistic, also called the Pearson r . The Pearson r is a statistical value that tells the strength and direction of the relationship between two normally distributed variables measured on an interval or ratio scale . Researchers examine the two sets of values and calculate a summary statistic called a correlation coefficient . The longer name for a common correlation statistic is the Pearson Product Moment Correlation Coefficient but sometimes it is referred to as the Pearson r . The symbol for correlation is a lower case and italicized r .  In behavioural research, we normally round values to two decimal points. A moderately strong positive correlation example is r = .78.       Sometimes, the relationsh...

  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...

 The Dependent Samples t test is used to test for significant differences between two sets of numerical data produced by the same organisms or organisms that are matched on all relevant variables. Dependent Samples t test Infographic Geoffrey W. Sutton & AI What you will find in this article. 1. Basic examples 2. Requirements to use the Dependent Samples t test 3. Two books professors recommend for students *4. A step by step procedure for calculation of a Dependent Samples t test *5. A detailed example of a calculation table with step by step calculations 6. An APA style results text. *7. An Calculator for you to enter your own data * AI code can contain errors- leave a message if you notice an error. Example: Same Group- Pre and Posttest In one example, a group of people who attend a workshop may complete a pretest and a posttest. A Dependent Samples t test can be used to compare the mean differences between the pretest and the posttest. Example: Two Groups: Matched Pairs ...

  Scale name: Foster Parent Experiences Measure   Scale overview This set of questions uses different ratings for different items.   Author(s ) Denby, Ramona, Rindfleisch, Nolan, & Bean, Gerald. (1999).   Items The items assess different experiences of foster parents.   Response Type Likert-type scales with different ranges.   Sample item From the Training Effect variable: “ I felt competent to handle the types of children placed in my home.” See the PsycTESTS references for more sample items.   Reliability & Validity Not included in the PsycTESTS entry.   Availability According to Science Direct , “Reprint requests should be addressed to Dr. Ramona Denby, University of Nevada Las Vegas, School of Social Work, 4505 Maryland Pkwy., Las Vegas, NV 89154”   Permissions -- if identified Test content may be reproduced and used for non-commercial research and educational purposes without seeking  written...