Lecture 3

• Desirable properties of psychological measurement include reliability, validity, and objectivity.
• Measures of variability is a type of statistic that describes the amount of variation in a distribution.
• Variability is an indication of how scores in a distribution are scattered or dispersed.
• Range refers to the difference between highest and lowest scores in a distribution, making it the simplest measure of variability but also the most limited.
• Quartile range is any of the three values which divide the data set into four equal parts, so that each part represents 1/4 th of the sample population.
• Interquartile range is the difference between the third and first quartiles and is a measure of statistical dispersion.
• Standard deviation is the measure of variability equal to the square root of the average square deviations of the mean while the variance (s2) is equal to the arithmetic mean of the squares of the difference between the scores in a distribution and their mean.
• Regardless of sample size, the distribution of sample means will be normally distributed.
• The mean of the distribution of sample means is the mean of the population.
• Sample size does not affect the center of the distribution.
• The standard deviation of the distribution of sample means, or the standard error, is spread out.
• Negative Skewed Distribution is when scores are more concentrated in the high end.
• Positive Skewed Distribution is when scores are more concentrated in the low end.
• Skewness measures of symmetry (information about the tendency), while kurtosis measures peakness.
• Standardization in psychological measurement is an agreement about the process of the test administration.
• Population norms in psychological measurement are necessary to interpret the scores from an individual or group, requiring a large representative or sample, solid standardization in administration and scoring, and great inter-rater reliability if subjective.
• Standardization in test administration involves specific instructions, order of items, timing etc.
• Scoring distribution in psychological measurement involves identifying what is high, low and normal scores, and identifying the cut-off scores to define important populations and subpopulations.
• Reliability in psychological measurement refers to the consistency of scores obtained by the same person when they are reexamined by the same test on different occasions, or with different set of equivalent items under the variable examining conditions.
• Scoring in psychological measurement involves correct, ‘partial’ and incorrect answers, points awarded.
• Validity in psychological measurement estimates how well a test measures what it purports to measure.
• Two major trends in validity are strengthened theoretical decisions and close linkage between psychological theory and verification through empirical and experimental hypothesis testing.
• Constructs in psychological measurement are broad categories, derived from common features shared by directly observable behavioral variables.
• Validity in psychological measurement leads to the growing recognition of the value of constructs in describing and understanding human behavior.
• Validity in psychological measurement can’t be reported in general terms, in terms of just high or low, it is established with references to the particular use it is being considered.
• Standardization of test administration ensures that the assessment is conducted under specific conditions which can be repeated and that the test are scored the same way.
• Psychometrics is a scientific discipline concerned with the construction of assessment tools, measurement instruments, and formalized models that may serve to connect observable phenomena (e.g., responses to items in an IQ-test) to theoretical attributes (e.g., intelligence).
• Psychometric properties are characteristics of tests and other measures of human characteristics that identify and describe attributes of an instrument, such as its reliability or appropriateness for use in a particular circumstance.
• 68% of scores are within 1 standard deviation of the mean.
• The development of refinement of theoretical approaches to measurement is another major research task in psychometrics.
• The Empirical Rule states that 99.7% of data observed following a normal distribution lies within 3 standard deviations of the mean.
• The 68-95-99 rule states that 25-8 (17) +8 (33) +8 (41) +8 (49) - 8 (9) - 8 (1) are standard normal deviations.
• 68% of people will be between 17 (25 - 8= 17) and 33 years ( 25+8= 33).
• Test user refers to the wide array of professionals who relay on psychological assessment and tools for various purposes.
• Test taker refers to the person whom the assessment tools were administered to.
• The construct of instruments and procedures for measurement is one of the major research tasks in psychometrics.
• If the normal average score of test takers is 75, how many SD is needed to get the score of 125 and 25 if the population mean is 20?
• 99.7% of scores are within 3 standard deviations of the mean.
• Desirable properties of psychological measurement include standardization, reliability, validity, population norms, and interpretability of individual results.
• 95% of scores are within 2 standard deviations of the mean.