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Chapter 2

Chapter 2 Psychology Testing Textbook, 7th edition

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Western University
Psychology 2080A/B
Doug Hazlewood

Chapter 2Statistical method serve two importnat purposes First statistics are used for purposes of description Second we can use it to make inferences which are logical deductions about events that cant be observed directly ex we dont know how many ppl watched tv can get that info by using scientific sample surveys Data gathering and analysis might be considered analogous to criminal investigation and prosecution First comes the detective work of gathering and displaying clues or what the statistician call explotatory data analysisThen comes a period confirmatory data analysis when the clues are evaluated against regid statistical rules Descriptive statistics are methods used to provide a concise description of a collection of quantitive information Inferential statistics are methods used to make inferences from observations of a small group of ppl known as a sample to a large group of individuals known as a population He or she observes a relativelly small group of subjects sample and uses inferential statistics to estimate the characteristics of the larger groupScale of measurementsOne may define measurements as the application of rules are the specific procedures used to transform qualities of attributes into numbers Properties of scales three important properties make scale of measurement different from one another magnitute equal intervals and an absolute 0Magnitute is the property of Moreness a scale has the property of magnitute if we can say that a particular instance of the attribute represents more less or equal amounts of the given quantity than does instance If the coach were to rank the teams by the number of games they have won then the new numbering system would have the property of magnituteA scale has a property of equal intervals if the difference between two points at any place on the scale has the same number of scale units When a scale has the property of equal intervals the relationship between the measured units and some outcome can be described bya straight line or a linear equation in the form YabX This equation shows that an increase in equal units on a given scale reflects equal increases in the meaningful correlates of units By examining the point on the figure 21 you an see that at first the relationship is nearly linear increases in manual dexterity are associated with increases in ratings of artwork Then the relationship becomes nonlinear the figure shows that after a manual dexterity score of approximetly 5 increases in dexterity produce relatively smaller increases in quality of artwork An absolute 0 is obtained when nothing of the property being measured exists For many psychological qualitites it is extremely difficult to define an absolute point 0Types of scales Nominal scale doesnt have the property of magnitute equal intervals or an absolute 0 Nomianl scales are really not scales at all Nominal scales are used when the information is qualitative rather then quantitative A scale with the property of magnitute but not equal intervals or an absolute 0 is an ordinal scale this scale allows u to rank individuals or objects but not to say anything about the meaning of the differences between the ranks For example IQ tests do not have the propertty of equal intervals or an absolutebut they do have the property of magnitute Because it doesnt
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