**Chapter 11**

**Data Analysis and Interpretation: Part I. Describing Data, Confidence Intervals, Correlation**

**Short Answer Questions**

*(p. 351-352)*Describe the advantages and disadvantages of the three measures of central tendency: mean, median, mode.

The mean is the most commonly used measure of central tendency. Because it is affected by a change in any score, the mean can be seriously affected by extreme values. The median is the middle point in the frequency distribution, above which half the scores fall and below which half the scores fall. The median, because it is based on the frequency of scores and not the value of scores, is appropriate when there are extreme values in the distribution. The mode is the score appearing most frequently in the distribution. It is the simplest to calculate but is often the least useful of the measures of central tendency.

*Level: Factual *

*(p. 357)*Why is a confidence interval also called a “margin of error”?

A confidence interval is also a margin of error because it identifies a range of values that we can expect from sampling error when estimating a population value such as the mean.

*Level: Factual *

*(p. 359)*What does the width of a confidence interval tell us, and how does the size of a sample affect the width of a confidence interval for a population mean?

The narrower the interval, the better is our estimate of the population mean. As sample size increases, the interval width decreases. Increasing sample size reduces both the critical *t* value and the standard error of the mean in the formula for the confidence interval.

*Level: Factual *

*(p. 359)*What does the “95” in a 95% confidence interval refer to?

The 95 in a 95% confidence interval refers to the fact that of 100 times an interval is constructed based on different random samples of this size from a population, 95 of the intervals will contain the population mean within the interval.

*Level: Factual *

*(p. 374-375)*Explain the phrase, “Correlation does not imply causation.”

A correlation is not sufficient evidence to support a causal statement. The coefficient summarizes the degree to which scores on two variables “go together.” That scores on two variables are correlated does not mean one variable causes the other. One possibility is that a third variable is causally related to both variables.

*Level: Conceptual *

** Multiple Choice Questions **

*(p. 343-344)*Which of the following is__not__a major stage of data analysis?

A. getting to know the data

B. confirming what the data reveal

transforming the data__C.__

D. summarizing the data

*Level: Factual *

*(p. 345)*A coherent “story” of data analysis for a study will include

A. an explanation of the findings.

B. counter arguments for opposing interpretations of the findings.

C. justifications for conclusions.

all of these__D.__

*Level: Factual *

*(p. 345)*Computer-assisted data analysis requires that the researcher have a good knowledge of

A. null hypothesis testing.

research design and statistics.__B.__

C. computer hardware.

D. computer software.

*Level: Factual *

*(p. 347-348)*Which of the following procedures would not be expected during the first stage of data analysis?

performing tests using inferential statistics__A.__

B. looking for outliers

C. visualizing the distribution with graphical displays

D. checking for errors

*Level: Factual *

*(p. 347)*A score that is extreme and does not “go with” other scores in the distribution is called an

A. error.

B. impossible value.

C. significant value.

outlier.__D.__

*Level: Factual *

*(p. 349)*If a stem-and-leaf display were created for the following set of numbers, 23, 24, 24, 21, 20, 27, 29, 28, we would expect the digit 2 to be a

A. leaf.

stem.__B.__

C. tree.

D. trunk.

*Level: Factual *

*(p. 349)*An advantage of a stem-and-leaf display is that

A. it is a graph of the mean, median, and mode.

B. it reveals whether the relationship between two variables is linear.

it reveals the shape of a distribution and the presence of any outliers.__C.__

D. the intervals tells us how well our sample mean estimates the population mean.

*Level: Factual *

*(p. 350)*Distributions of scores for two groups in an experiment can be compared by

A. arranging the “stems” for both groups in one stem-and-leaf display and the “leaves” for both groups in a second stem-and-leaf display.

B. preparing one stem-and-leaf display using the scores for both groups.

arranging a stem-and-leaf display for each group side-by-side.__C.__

D. none of these

*Level: Factual *

*(p. 351)*The value that splits a frequency distribution into two halves, each half with the same number of values, is the

A. mode.

B. mean.

median.__C.__

D. standard deviation.

*Level: Factual *

*(p. 352)*The ____________ is the best measure of central tendency when there are extreme values in the distribution.

A. mode

median__B.__

C. mean

D. variance

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