
Standard Deviation
 average deviation from the mean in the original
 unit of measurement.

Normal distributions
the mean, mode, and median are the same. Bellshaped & symmetrical

Positivelyskewed
distribution
majority of scores on the lower end of range (the mean is more positive than mode and median).

Negativelyskewed
majority of scoreson the higher end (mean is more negative than mode and median.

Reliability
consistent,true. Is a psychometric indicator ofquality of an instrument. Consistencywhen test is repeated.

Reliability coefficients
 can be calculated to provide an indication of
 the amount of measurement error.
 Example: on a 01 scale, .8=80% reliability. Based on the amount of consistency between
 two sets of scores.

Correlation
 the statistical technique used to calculate this
 consistency

Positive correlation
scores are consistent in the same direction

Negative correlation
scores are consistent in different directions, so as scores on one test increase, scores on another decrease

Standard Error of Measurement (SEM)
helpful in interpreting an individual’s score. Provides an estimation of the range of scores that would be obtained if someone took an instrument over and over again. Takes reliability into account.

Validity
 concerns what an instrument measures and how well it does it. Instruments are not valid, uses of instruments are.
 *Reliability is a prerequisite to validity. If there is too much error, the instrument can’t measure anything consistently.

Convergent evidence
positive relationship of instrument with other variables with which it should theoretically be related. *High=if it agrees

Discriminant evidence
no relationship or negative relationship of instrument with variables from which it should differ in these ways. *Low=it disagrees. (Happiness/stress/anxiety)

Normreferenced
in comparison to others

Norming group
group who took the instrument to which others’ scores are then compared

Mode
most frequent score in a distribution

Median
the score where half the people had a score below it and half had a score above, evenly dividing the scores in half

Mean
average of the scores

Frequency Distribution
Can interpret scores more accurately if scores are tallied this way. (Ex: clas has 30 students, these are their scores....)

Normal curve
 largest mumber of cases cluster in center (68)
 Bellshpaed

Scales of Measurement
Nominal, Ordinal, Interval, Ratio

Nominal
 Numbers are used to classify and identify persons
 Numbers are substituted for names or verbal labels

Ordinal
Assigns numbers in rank order

Interval
Helps when interested in differences or intervals between things

Ratio
 Only scale where you can say "twice as...x"
 Ratios between the umbers assigned to the person or object
 Corresponds to the ratios between the attributes measured in these things
 Addresses issues of relative size, weight, speed, etc. of 2 objects

