Midterm 1 - Scales, distributions & norms (Ch. 2) Flashcards
What are the 3 key properties of scales?
- magnitude: “moreness” (when we can say one instance has more/equal/less of an attribute compared to another)
- equal intervals: diff btw 2 points at any point on scale has same meaning as diff btw any 2 other points (IQ does NOT have equal intervals, diff btw 45 and 50 means smt diff than btw 105 and 110)
- absolute zero: when nothing of property measured exists
IQ can be considered a(n) ____ scale
ordinal! (has property of magnitude but not equal intervals or absolute zero)
Which of the 3 properties does each type of scale have?
- Nominal
- Ordinal
- Interval
- Ratio
- Nominal: none
- Ordinal: magnitude
- Interval: magnitude, equal intervals
- Ratio: magnitude, equal intervals, absolute zero
What type of scale is most commonly used in psychological research/testing?
interval (eg Likert scale)
In a nominal scale, numbers are assigned to represent _____. Appropriate statistics for these scales are _______.
labels or categories of data only
frequency, mode
In an ordinal scale, numbers are assigned to _____. The distances between numbers are _____. Appropriate statistics for these scales are _______.
rank-ordered data; NOT equal
frequency, mode, median, percentile, rank-order correlation
In an interval scale, numbers are assigned to _____. The distances between numbers are _____ and there (is/is not) an absolute zero point. Appropriate statistics for these scales are _______.
rank-ordered data; judged to be equal; is NOT
frequency, mean, mode, median, percentile, Pearson correlation, t-test
In a ratio scale, numbers are assigned to _____. The distances between numbers are _____ and there (is/is not) an absolute zero point. Appropriate statistics for these scales are _______.
rank-ordered data; equal; IS absolute 0
frequency, mean, mode, median, percentile, Pearson correlation, proportion, t-test
What are the 3 types of norms presented in class?
- Developmental norms (use norm sample)
- Within-group norms (use norm sample)
- Criterion-referenced norms (no norm sample)
For developmental norms, age-equivalent or grade-equivalent scores are assigned based on the ______ score for that chronological age or grade level
median raw score (using mean would assume normal distribution and no outliers)
Within-group norms use _____
standard scores (z-scores)
A percentile reflects the percentage of individuals ____
falling below a score (eg if you score 90th percentile, 90% of ppl scored lower than you)
What is the formula for percentiles?
(nL/N) x100
nL (number of ppl w lower score)
N (number of ppl in sample)
Z-scores tell us ______
how far from the mean a score is
A the curve for a normal distribution with a larger SD would (taller/flatter) vs a smaller SD
flatter (smaller SD is a tall spike)
Standard deviation is a measure of ____
the avg distance of scores from the mean
what is the formula for z transformation?
z = (X-M)/SD
X (raw score)
M (mean)
transformed standard scores involve a ____ transformation of z-scores.
The transformed standard score = _____ + _____
linear!
Bz + A
A = mean, B = SD of transformed scores
In normal distributions, __% of scores fall below the mean.
About __% of scores fall between the mean and 1 SD.
About __% of scores fall below 1 SD below the mean.
50%
34%
16%
In a normal distribution:
__% of scores fall between -/+1 SD
__% of scores fall between -/+2 SD
__% of scores fall between -/+3 SD
68%
95%
99.7%
What is the percentile for a z score of 1? what about -2?
84th percentile; 2.5th percentile
When standard scores are near the mean, (small/large) diffs in scores correspond to (small/large) diffs in percentile
small; large
T scores have a M of __ and SD of __
M = 50; SD = 10
(T/F) you can use percentiles w ordinal and nominal scales
FALSE ordinal but not nominal
What are 2 disadvantages of using percentiles?
- magnifies diffs near men, minimizes diffs at extremes
- some common stat analyses not possible w percentiles
What are 2 disadvantages of standard scores (z-scores)?
- unfamiliar to many non-specialists
- interpretation difficult when distribution not normal
What are 2 common criticisms of within-group norms?
- only meaningful if norm sample is representative
- within group comparisons encourage competition
Criterion-referenced norms evaluate scores relative to ___ rather than ____
a standard rather than other individuals
WHat are 3 problems w criterion-referenced norms?
- hard to specifically define elements of performance
- focus is just on reaching a certain minimum standard
- absence of relative knowledge
In clinical contexts, what is considered an elevated/atypical z-score?
+/-2z
What are 3 key characteristics of a good norm sample?
- sufficiently large (usually more representative)
- representative of target population
- contemporary/current
