Test theory and psychometrics Flashcards
What must you know about a test to use it?
- Name of test
- Type of distribution
- Definition of construct
- Standardisation or raw?
- Norms / cut offs / population
- Evidence used to support measures - validity
- M and SD
- Out of
- Experience of Tester
What is a distribution?
A set of test scores
What are raw scores?
unmodified scores of test performance
What is frequency distribution?
a tally of the number of score occurrences
What is a grouped frequency distribution?
Scores that fall within intervals are counted (95-99 etc.)
How can we describe the distribution of test scores?
Using:
measures of central tendency
measures of variability/ dispersion
What are the measures of central tendency?
mean, medium and mode
What are the measures of variability/ dispersion?
range, standard deviation
What does SD mean?
The average distance from the mean
What is used to develop norms?
Standard scores
What is a normative sample?
A group of people’s scores who are used as reference
Norms are?
test performance data for reference
What is a criterion?
A standard on which a judgement or decision is based: e.g. GPA x to get into a course
How many scores in a normal distribution fall above and below the mean?
50:50
How many scores in a normal distribution occur between the mean and 1 SD?
34%
How many scores in a normal distribution occur between +-1 SD? e.g. -1 SD to +1 SD
68% (34% on each side)
How many scores in a normal distribution occur between +-2 SD? e.g. -2 SD to +2 SD
96% (48% on each side)
How many scores in a normal distribution occur fall above 2SD?
2% (on each side)
How many scores in a normal distribution occur fall between 1SD and 2SD?
14% (on each side)
What does 75th percentile mean?
higher than 75% of people (in the top 25%)
What are the limitations of using percentiles?
changes all of the time
may not give an accurate reading
if ordinal data it looses precision
Why don’t we just give raw scores?
For broader meaning/ comparison
What is the simplest example of a standard score?
z score
What is the formula for calculating a z score?
z = x - mean / SD
What is the mean for a set of z scores?
0
What is the SD for a set of z scores?
1 SD
What does a z score tell us?
How many SD the raw score is below or above the mean