Textbook Notes (367,754)
Canada (161,370)
Psychology (3,330)
PSYC 3250 (62)
Chapter 2

Chapter 2.docx

6 Pages
112 Views
Unlock Document

Department
Psychology
Course
PSYC 3250
Professor
Jeffrey Spence
Semester
Winter

Description
Chapter 2: The Basic Statistic of Measurement The Role of Mathematics in Assessment Scales of Measurement - what is measurement? o measurement - set of rules for assigning numbers to represent objects, traits, attributes, or behaviours o psychological tests – measuring devices, involve rules for assigning numbers to an individual’s performance that are interpreted as reflecting characteristics of the individual o scale of measurement – units of measurement have this mathematical property o scale – system or scheme for assigning values or scores to the characteristic being measured o Stevens  proposed a taxonomy that specified 4 scales of measurement • nominal, ordinal, interval, and ratio - nominal scales o nominal scales  simplest  classify people or objects into categories, classes, or sets  can assign numbers simply to identify or label categories • categories are not ordered in a meaningful manner • assignment of numbers is completely arbitrary • serve only as names for the categories • numbers should not be added, subtracted, ranked, or otherwise manipulated - ordinal scales o ordinal scales - rank people or objects according to the amount of a characteristic they display or possess o enable use to quantify the variables under examination and provide substantially more information than nominal scales o provides quantitative information  does not ensure that the intervals between the ranks are consistent o indicate the rank-order position among individuals or objects, but they do not indicate the extent by which they differ o somewhat limited in both the measurement information they provide and the statistical procedures that can be applied o examples – percentile rank, age equivalents, and grade equivalents - interval scales o interval scales - rank people or objects like an ordinal scale but on a scale with equal units o equal scale unit – difference between adjacent units on the scale is equivalent o many psychological tests are designed to produce interval-level scores  can be manipulated using common mathematical operations, whereas less scales cannot o most statistical procedures can be used with interval scale data o limitation  no true zero • zero does not reflect the total absence of the attribute  ratios are not meaningful o behavioural variables  intelligence or personality characteristics – don’t know where the true zero lies o physical characteristics  zero point is well defined o derived by first locating the midpoint of a variable and then measuring outward in each direction, above and below, as far as we can establish scores with reasonable accuracy o psychology  interval scale scores are most commonly seen in the form of standard scores - ratio scales o ratio scales - have the properties of interval scales plus a true zero point that reflects the complete absence of the characteristic being measured o not meaningful or interpretable with other scales o few ratios in psychological measurement - hierarchy among the scales o nominal scales  least sophisticated and providing the least information  allowed to assign a number to a person that associates the person with a set or category  other useful quantitative properties are missing o ratio scales  most sophisticated and providing the most information  have all the positive properties of nominal scales with addition of the ability to rank people according to the amount of a characteristic they possess  have all the positive properties of an interval scale with the addition of an absolute zero point • allows one to form meaningful ratios between scores o interval scales  have all the positive properties of ordinal scales and incorporate equal scale units • allows one to make relative statements regarding scores The Description of Test Scores - to interpret or describe test scores meaningfully you need to have a frame of reference - often the frame of reference is how other people performed on the test - distributions o distribution - set of scores o represented – tables and graphs o grouped frequency  possible scores are “combined” or “grouped” into class intervals that encompass a range of possible scores o frequency graphs  popular and provide a visual representation of a distribution  x-axis – scores  y-axis – frequency of scores o symmetrical distributions o skewed distributions – positively or negatively - measures of central tendency o many distributions tend to concentrate around a center o 3 measures of central tendency  mean, median, and mode o mean  mean – arithmetic average of a distribution  MEAN = SUM OF SCORES/ NUMBERS OF SCORES  useful in providing a sense of the central tendency of the groups of scores • 1. mean is meaningful for distributions containing interval and ratio level scores • 2. mean of a sample is a good estimate of the mean for the population from which the same was drawn • 3. essential to the definition and calculation of other descriptive statistics that are useful in the context of measurement  undesirable characteristic • sensitive to unbalanced extreme scores • influence of an extreme score decreases as the total number of scores in the distribution increases Box: Population Parameters and Sample Statistics • population – complete group of people, objects, or other things of interest • sample – subset of the larger population that is though to be representative of the population • population values – parameters and are represented by Greek symbols o mu (u) – indicate a population mean o sigma (o) – indicate a population standard deviation • statistic – value that is calculated based on a sample and represented by Roman letters o sample statistics can provide information about the corresponding population parameters o median  median – score or potential score that divides a distribution in half  calculated for distributions containing ratio, interval, or ordinal level scores • not appropriate for nominal level score  useful and versatile measure of central tendency that is particularly useful for many common descriptive purposes o mode  mode – most frequently occurring score in a distribution  advantage • can be used with nominal, ordinal, interval, and ratio data  limitations • 1. some distributions have two scores that are equal in frequency and higher than other scores o bimodal distribution  mode is ineffective as a measure of central tendency • 2. mode is not a stable measure of central tendency o choosing between the mean, median, and mode  which measure of central tendency is most useful and appropriate? • mean o essential when calculating other useful statistics o considerable utility as a measure of central tendency • median o most versatile and useful measure of central
More Less

Related notes for PSYC 3250

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit