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. 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. An example of a Matched Pairs t test can be used to compare two groups of people in a reading method experiment. A relevant variable would be reading ability. A reading test could be used to identify people with similar scores. One member of the pair is then randomly assigned to a new reading method group and the matching person is then assigned to the traditional reading group. At the end of the study, a Matched Pairs t test can be used to compare mean scores for the groups. When the same person produces two sets of scores, each person is their own control. Because of the level of cont...

  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...

Scale name: Positive Home Integration Scale (PHIS) Scale overview The PHIS is a 9-item Likert-type rating scale. “This article introduces a youth-reported measure (Essential Youth Experiences [EYE]) developed to assess the experiences of foster youth in their home environment and their critical relationships across a number of service systems.” (From the Abstract) Author(s) Kothari, Brianne H., McBeath, Bowen, Bank, Lew, Sorenson, Paul, Waid, Jeff, & Webb, Sara Jade. (2018 Items = 9 Response Type Ratings from 1 to 10 with two anchors (they vary with the item) and a midrange label (somewhat). Subscales None identified in the PsycTESTS source. Sample item To what extent do you feel that you are treated with kindness in your (foster) home?   Reliability & Validity See the article reference for psychometric properties.   Availability The full set of 9 items with the 10-point descriptive labels can be found in the PsycTESTS reference below. ...

  Scale name: Family Stress Measure   Scale overview The five questions on the Family Stress Scale were rated on a 5-point Likert scale ranging from never to very often .   Author(s) Geiger, J. M., Hayes, M. J., & Lietz, C. A. (2013) Items = 5   Response Type: Likert-type, 5-point   Sample item How often have you experienced any of the following events: 1. Severe difficulties with your foster child's biological family/parents?   Reliability/ Validity Not reported in PsycTESTS entry.   Availability The 5-items are listed in the PsycTESTS entry. Geiger, J. M., Hayes, M. J., & Lietz, C. A. (2013). Family Stress Measure [Database record]. Retrieved from PsycTESTS. doi: https://dx.doi.org/10.1037/t25361-000   Permissions -- if identified “Test content may be reproduced and used for non-commercial research and educational purposes without seeking written permission. Distribution must be controlled, meaning on...