Exam 3: Measures of Variability

The Children's Depression Inventory (CDI), developed from Beck's Depression Inventory is a self-report instrument with 27 sets of statements. Higher scores indicate higher levels of depression. Scores above 13 are said to indicate a Major Depressive Disorder (MDD) and few false positives have been reported. A random sample of 20 fifth grade students was selected and given the test. Their scores were as follows: 9,10,11,9,8,9,17,2,7,11,6,12,9,10,9,9,8,10,14,1. -Find the median score for the group.

A researcher gives IQ tests to a large group of adults, and discovers that the mean, median and mode all equal 100. The highest score in the group was 130 and the lowest was 70. Between IQ's of 75 and 125, 80% of the group was found, and 50% were found between IQ's of 90 and 110. The shape of the graphed distribution was mesokurtic. -The interdecile range was equal to

A researcher wished to evaluate the operating life of a certain brand of storage battery. A group of 30, brand-new batteries was selected and placed in 30 identical automobiles. The lights in each automobile were then turned on (without running the engines), and the length of time before the batteries were fully discharged (lights went out) was recorded. The scores, in hours, were: 15, 10, 20, 18, 18, 11, 11, 11, 11, 12, 12, 12, 10, 9, 9, 8, 9, 9, 11, 11, 11, 15, 12, 12, 12, 10, 12, 12, 15, 12. -Calculate the mean.

When most scores cluster closely around the mean, the curve is

A researcher wished to evaluate the operating life of a certain brand of storage battery. A group of 30, brand-new batteries was selected and placed in 30 identical automobiles. The lights in each automobile were then turned on (without running the engines), and the length of time before the batteries were fully discharged (lights went out) was recorded. The scores, in hours, were: 15, 10, 20, 18, 18, 11, 11, 11, 11, 12, 12, 12, 10, 9, 9, 8, 9, 9, 11, 11, 11, 15, 12, 12, 12, 10, 12, 12, 15, 12. -Calculate the standard deviation.

A researcher gives IQ tests to a large group of adults, and discovers that the mean, median and mode all equal 100. The highest score in the group was 130 and the lowest was 70. Between IQ's of 75 and 125, 80% of the group was found, and 50% were found between IQ's of 90 and 110. The shape of the graphed distribution was mesokurtic. -The second quartile coincided with an IQ of

The median must always coincide with the fifth decile.

When the vast majority of scores cluster tightly around the mean, the graphed distribution is leptokurtic.

The only time the standard deviation may equal zero, is when

A platykurtic distribution always has

The deviation score is

The standard deviation may never be larger than the range. 33

A researcher gives IQ tests to a large group of adults, and discovers that the mean, median and mode all equal 100. The highest score in the group was 130 and the lowest was 70. Between IQ's of 75 and 125, 80% of the group was found, and 50% were found between IQ's of 90 and 110. The shape of the graphed distribution was mesokurtic. -The range was equal to

When an extremely homogeneous set of scores is graphed, then the resulting frequency distribution curve is

A researcher wished to evaluate the operating life of a certain brand of storage battery. A group of 30, brand-new batteries was selected and placed in 30 identical automobiles. The lights in each automobile were then turned on (without running the engines), and the length of time before the batteries were fully discharged (lights went out) was recorded. The scores, in hours, were: 15, 10, 20, 18, 18, 11, 11, 11, 11, 12, 12, 12, 10, 9, 9, 8, 9, 9, 11, 11, 11, 15, 12, 12, 12, 10, 12, 12, 15, 12. -Calculate the variance.

The interquartile range includes the middle-most

A group of inmates at a State House of Correction were tested during orientation on the LSI (Level of Security Inventory) to assess their possible security risk while incarcerated. Their scores were as follows: 4,8,2,4,6,5,7,3,4,6,5,7,4,5,4,3,7,6,5,5. -Evaluate the distribution for Skewness

One major defect of the range is that

A researcher wished to evaluate the operating life of a certain brand of storage battery. A group of 30, brand-new batteries was selected and placed in 30 identical automobiles. The lights in each automobile were then turned on (without running the engines), and the length of time before the batteries were fully discharged (lights went out) was recorded. The scores, in hours, were: 15, 10, 20, 18, 18, 11, 11, 11, 11, 12, 12, 12, 10, 9, 9, 8, 9, 9, 11, 11, 11, 15, 12, 12, 12, 10, 12, 12, 15, 12. -For the following set of scores, calculate the standard deviation:. 13, 14, 12, 15, 10, 7, 12