Ch3: Norms & Reliability

Question 1

Mean

Answer 1

Add all divide by total number (Average)

Question 2

Median

Answer 2

The middle most score when all scores have been ranked

Question 3

Mode

Answer 3

The most frequently occurring score.

If two scores tie for the highest frequency or occur ace, the distribution is said to be BIMODAL

Question 4

Histogram

Answer 4

Provides a graphic representation of the same info contained in the frequency distribution

Question 5

Frequency Polygon

Answer 5

Similar to histogram, except that the frequency of the class, e.g., intervals is represented by single points rather than columns

Question 6

Norm Group

Answer 6

Consists of a sample of examiners who are representative of the population for whom the test is intended.

Question 7

Raw Score

Answer 7

Not useful by themselves

Question 8

Frequency Distribution

Answer 8

Is prepared by specifying a small number of usually equal-sized class intervals and then tallying how many scores fall within each interval. The sums of the frequencies for all intervals will equal N, the total number of scores in the sample

Question 9

Measures of Variability

Standard Deviation

Answer 9

Designated as s or abbreviated as SD.

Reflects the degree of dispersion in a group of scores

If the scores are tightly packed the SD is small. In fact, in the extreme case in which all the scores are identical, the SD is exactly 0.

As the group of scores become more spread out, the SD becomes larger.

Question 10

Variance Formula

Answer 10

See pg 49

square root of the variance

Question 11

Variance

Answer 11

The measure of variability

SD is the preferred measure of variance in psych testing because of its relevance to the normal distribution

Question 12

Normal Distribution

Answer 12

Bell-shaped curve

Preferred by psychologists
1) because it has useful mathematical features that form the basis for several kinds of statistical investigation

2) Mathematical precision
3) A normal curve arises spontaneously in nature

Question 13

Skewness

Answer 13

Refers to the symmetry or asymmetry of a frequency distribution

If scores are piled up at the low end of the scale, the distribution is said to be positively skewed

In the opposite case, when test scores are piled at the high end of the scale, the distribution is said to be negatively skewed

Question 14

In psych testing, skewed distributions usually signify

Answer 14

The test developer has included too few easy items or too few hard items

Question 15

Percentile

Answer 15

Expresses the percentage of persons in the standardization sample who scored below a specific raw score.

A percentile indicates only how an examiner compares to the standardization sample and does not convey the percentage of questions answered correctly

E.g., pg 51, paragraph 2

Question 16

Do percentile scores have drawbacks?

Answer 16

They distort the underlying measurement scale, especially at the extremes

Question 17

Standard Scores (aka Z scores)

Answer 17

Expresses the distance from the mean in standard deviation units

Uses the standard deviation of the total distribution of raw scores as the fundamental unit of measurement

Possess the desirable psychometric property of retaining the relative magnitudes of distances between successive values found in the original raw scores.

Question 18

Formula for computing standard score:

Answer 18

Subtract the mean of the normative group from the examiner’ s raw score and then divide this difference by the standard deviation of the normative group