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Ratio
 Real measurements
 ex. height, weight, speed, velocity, mass, area, volume
 there is a true 0 point
 this means that division and multiplication are meaningful
 experimental psychology tends to use ratio measurements

Experimental psychology ratios
 accuracy
 reaction time
 heartrate
 brain waves
 response rates of pigeon or rate in a Skinner box

Interval
 quantitative variable
 like ratio measurement
 There is NO true 0 point
 Sums and differences are meaningful, but not multiplication and division (ratios)

Interval examples
 temperature scales, including Celsius and FAhrenheit
 clock or calender time, because we dont know when time started

Interval level measurements
 In testing, personality and social psychology we frequently use questionnaire and test responses such as Liket (agreedisagree) scales
 usually convert these to numbers and use math on them, so we are treating them as interval scales.
 may be considered ordinal scales

Nominal
 categories without order
 there are no numbers
 sometimes we use numbers as categories
 ex. social security numbers
 numbers on football jersies
 telephone numbers

how do you do statistics with nominal variables
it requires a trick, count the number of items in each category

Ordinal
 Ordered categories
 freshman, sophomore, junior, senior
 Nominal and ordinal are similar
 the distances between each point are not neccessarily equal

Levels of measurement have a natural order, from strong to weak
 Strong: Ratio; Interval (quantitative)
 Weak: Ordinal;Nominal (qualitative/catergorical)

Permissible operations
all levels of measurement have certain mathematical operations that are allowed, and others that are not allowed

Permissible operations: Ratio variables
Multiplication and division (ratio) operations ar permitted because there is a true 0 point

Permissble operations: Interval variables
addition and subtraction ar allowed, but not division and multiplication

Permissible operations: ordinal variables
comparison of less and more are allowed, but not the other mathematical operations

Permissible operations: nominal variables
comparison of same or different are allowed, but not less or more, or any other mathematical operations

Demotion
 Involves throwing away information
 ex Rank height

Promotion
 Involves adding information that you dont have
 ex. GPA calculator

Norm Referencing
 each score is compared to the average of a reference group
 grading on a curve is an application
 ex IQ testsĀ
 SAT, GRE
 Personality inventories

Criterion referencing
 each score is compared to an absolute standard
 these are generally used when absolute performance levels are set
 Ex. DMV written exams
 State K12 testing (No Child Left Behind)
 PACT

Percentile
it depends on how many ppl took the test to determine how good the rank is

Standard scores
 obtained from raw scores by converting the distribution to one with a new mean and standard deviation
 Z scores are the most common

Z scores
once z score is obtained we can convert this to a percentile by looking up the z scored on a table of the normal distibution

grade equivalents
 publishers cheat
 based on z scores for the same school grade, not different school grades

SEM
 standard error of measurement
 test scores vary randomly
 ppl test scores may vary from their true scores
 measures how far a test score is likely to be from the true score (it is a kind of standard deviation of measurment)

True score
a real score that would be obtained by giving the test over and over again and averaging the results

