Which of the following best describes the meaning of standard deviation for a given variable?

Lesson 2: Summarizing Data

Self-Assessment Quiz

Now that you have read Lesson 2 and have completed the exercises, you should be ready to take the self-assessment quiz. This quiz is designed to help you assess how well you have learned the content of this lesson. You may refer to the lesson text whenever you are unsure of the answer.

Unless instructed otherwise, choose ALL correct answers for each question.

Use Table 2.16 for Questions 1 and 2, and for Questions 10–13.

Table 2.16 Admitting Clinical Characteristics of Patients with Severe Acute Respiratory Syndrome — Singapore, March–May, 2003

* Date of onset not provided in manuscript

† C=cough, D=dyspnea, F=fever, H=headache, M=myalgia, S=sore throat

‡ Normal > 1.50 × 10 −9/L

¶ HCW = health-care worker

Data Source: Singh K, Hsu L-Y, Villacian JS, Habib A, Fisher D, Tambyah PA. Severe acute respiratory syndrome: lessons from Singapore. Emerg Infect Dis 2003;9:1294–8.

1. Table 2.16 is an example of a/an _______________________________________ .
2. For each of the following variables included in Table 2.16, identify if it is:
   • Ordinal
   • Qualitative
   • Quantitative
   • Ratio
   • Categorical
   • Continuous
   • Interval
   • Nominal
   1. ____ Sex
   2. ____ Age
   3. ____ Lymphocyte Count
3. Which of the following best describes the similarities and differences in the three distributions shown in Figure 2.11?

   Figure 2.11

   
   1. Same mean, median, mode; different standard deviation
   2. Same mean, median, mode; same standard deviation
   3. Different mean, median, mode; different standard deviation
   4. Different mean, median, mode; same standard deviation
4. Which of the following terms accurately describe the distribution shown in Figure 2.12?

   Figure 2.12

   
   1. Negatively skewed
   2. Positively skewed
   3. Skewed to the right
   4. Skewed to the left
   5. Asymmetrical
5. What is the likely relationship between mean, median, and mode of the distribution shown in Figure 2.12?
   1. Mean < median < mode
   2. Mean = median = mode
   3. Mean > median > mode
   4. Mode < mean and median, but cannot tell relationship between mean and median
6. The mode is the value that:
   1. Is midway between the lowest and highest value
   2. Occurs most often
   3. Has half the observations below it and half above it
   4. Is statistically closest to all of the values in the distribution
7. The median is the value that:
   1. Is midway between the lowest and highest value
   2. Occurs most often
   3. Has half the observations below it and half above it
   4. Is statistically closest to all of the values in the distribution
8. The mean is the value that:
   1. Is midway between the lowest and highest value
   2. Occurs most often
   3. Has half the observations below it and half above it
   4. Is statistically closest to all of the values in the distribution
9. The geometric mean is the value that:
   1. Is midway between the lowest and highest value on a log scale
   2. Occurs most often on a log scale
   3. Has half the observations below it and half above it on a log scale
   4. Is statistically closest to all of the values in the distribution on a log scale

Use Table 2.16 for Questions 10–13. Note that the sum of the 14 temperatures listed in Table 2.16 is 531.6.

1. The mode of the temperatures listed in Table 2.16 is:
   1. 37.35°C
   2. 37.9°C
   3. 38.0°C
   4. 38.35°C
   5. 38.5°C
2. The median of the temperatures listed in Table 2.16 is:
   1. 37.35°C
   2. 37.9°C
   3. 38.0°C
   4. 38.35°C
   5. 38.5°C
3. The mean of the temperatures listed in Table 2.16 is:
   1. 37.35°C
   2. 37.9°C
   3. 38.0°C
   4. 38.35°C
   5. 38.5°C
4. The midrange of the temperatures listed in Table 2.16 is:
   1. 37.35°C
   2. 37.9°C
   3. 38.0°C
   4. 38.35°C
   5. 38.5°C
5. In epidemiology, the measure of central location generally preferred for summarizing skewed data such as incubation periods is the:
   1. Mean
   2. Median
   3. Midrange
   4. Mode
6. The measure of central location generally preferred for additional statistical analysis is the:
   1. Mean
   2. Median
   3. Midrange
   4. Mode
7. Which of the following are considered measures of spread?
   1. Interquartile range
   2. Percentile
   3. Range
   4. Standard deviation
8. The measure of spread most affected by one extreme value is the:
   1. Interquartile range
   2. Range
   3. Standard deviation
   4. Mean
9. The interquartile range covers what proportion of a distribution?
   1. 25%
   2. 50%
   3. 75%
   4. 100%
10. The measure of central location most commonly used with the interquartile range is the:
    1. Arithmetic mean
    2. Geometric mean
    3. Median
    4. Midrange
    5. Mode
11. The measure of central location most commonly used with the standard deviation is the:
    1. Arithmetic mean
    2. Median
    3. Midrange
    4. Mode
12. The algebraic relationship between the variance and standard deviation is that:
    1. The standard deviation is the square root of the variance
    2. The variance is the square root of the standard deviation
    3. The standard deviation is the variance divided by the square root of n
    4. The variance is the standard deviation divided by the square root of n
13. Before calculating a standard deviation, one should ensure that:
    1. The data are somewhat normally distributed
    2. The total number of observations is at least 50
    3. The variable is an interval-scale or ratio-scale variable
    4. The calculator or software has a square-root function
14. Simply by scanning the values in each distribution below, identify the distribution with the largest standard deviation.
    1. 1, 10, 15, 18, 20, 20, 22, 25, 30, 39
    2. 1, 3, 8, 10, 20, 20, 30, 32, 37, 39
    3. 1, 15, 17, 19, 20, 20, 21, 23, 25, 39
    4. 41, 42, 43, 44, 45, 45, 46, 47, 48, 49
15. Given the area under a normal curve, which two of the following ranges are the same? (Circle the TWO that are the same.)
    1. From the 2.5th percentile to the 97.5th percentile
    2. From the 5th percentile to the 95th percentile
    3. From the 25th percentile to the 75th percentile
    4. From 1 standard deviation below the mean to 1 standard deviation above the mean
    5. From 1.96 standard deviations below the mean to 1.96 standard deviations above the mean
16. The primary use of the standard error of the mean is in calculating the:
    1. confidence interval
    2. error rate
    3. standard deviation
    4. variance

Figure 2.11

Description: Three symmetrical bell curves. One is short and wide. One is tall and narrow. One is in between. They all have the same central location. Return to text.

Figure 2.12

Description: Histogram showing number of cases per day for an outbreak. There are a higher number of cases per day at the beginning of the outbreak and fewer cases per day for a long period of time near the end of the outbreak. Return to text.

Which of the following best describes the meaning of standard deviation?

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