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29 Cards in this Set
- Front
- Back
Descriptive Statistics are used for what? |
to simplify and summarize data |
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Inferential Statistics are used for what? |
to make general conclusions about populations using sample data. |
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How could a difference be caused by the treatments? |
Treatments 1 & 2 affect individuals differently, so the scores of the individuals receiving treatment 1 are different from those of individuals receiving treatment 2. |
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How could a difference simply be sampling error? |
The two treatments do not have different effects, but the individuals in one sampledo not behave exactly like the individuals in the second sample. |
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What additional information is obtained from measurements on an ordinal scale compared to measurements on a nominal scale? |
The direction of the difference between 2 measurements |
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What additional information is obtained from measurements on an interval scale compared to measurements on an ordinal sclae? |
The magnitude of the difference between 2 measurements |
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What additional information is obtained from measurements on a ratio scale compared to measurements on an interval scale? |
the relative sizes of two measurements |
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A numerical value that describes a sample data set is called a |
statistic |
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A numerical value that describes a population data set is called a |
parameter |
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Why is it necessary to have more than one method for measuring central tendency? |
Because no single method works well in all situations. |
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Why is the mean often not a good measure of central tendency for a skewed distribution? |
Extreme scores can displace the mean toward the tail |
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For a negatively skewed distribution with a mean of M=20, what is the most probable value for the median? |
greater than 20 |
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For a perfectly symmetrical distribution with a median of 30, what is the value of the mean? |
30 |
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Describe the data for a correlational research study. |
A correlational study has only one group of individuals and measures two (or more) different variables for each individual. |
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experimental? |
manipulating 2 variables |
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nonexperimental? |
observation |
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f? |
frequency of X |
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What general purpose is served by a good measure of central tendency? |
The purpose of central tendency is to identify a single score that serves as the best representative for an entire distribution, usually a score from the center of the distribution. |
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Identify the circumstances in which the median rather than the mean is the preferred measure of central tendency. |
The median is used instead of the mean when there is a skewed distribution (a few extreme scores), an open-ended distribution, undetermined scores, or an ordinal scale. |
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SS |
SS is the sum of squared deviation scores. |
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Variance |
Variance is the mean squared deviation. |
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Standard deviation |
Standard deviation is the square root of the variance. It provides a measure of the standard distance from the mean. |
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Is it possible to obtain a negative value for the variance or the standard deviation? |
Standard deviation and variance are measures of distance and are always greater than or equal to zero. |
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Explain why the formulas for sample variance and population variance are different. |
Without some correction, the sample variance underestimates the variance for the population. Changing the formula for sample variance (using n − 1 instead of N) is the necessary correction. |
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After 3 points have been added to every score in a sample, the mean is found to be M = 83 and the standard deviation is s = 8. What were the values for the mean and standard deviation for the original sample? |
The original mean is M = 80 and the standard deviation is s = 8. |
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After every score in a sample has been multiplied by 4, the mean is found to be M = 48 and the standard deviation is s = 12. What were the values for the mean and standard deviation for the original sample? |
The original mean is M = 12 and the standard deviation is s = 3. |
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What information is provided by the sign (+/−) of a z-score? What information is provided by the numerical value of the z-score? |
The sign of the z-score tells whether the location is above (+) or below (−) the mean, and the magnitude tells the distance from the mean in terms of the number of standard deviations. |
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What are the two requirements that must be satisfied for a random sample? |
The two requirements for a random sample are: (1) each individual has an equal chance of being selected, and (2) if more than one individual is selected, the probabilities must stay constant for all selections. |
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What information is provided by the sign (+ or −) of the Pearson correlation? |
A positive correlation indicates that X and Y change in the same direction: As X increases, Y also increases. A negative correlation indicates that X and Y tend to change in opposite directions: As X increases, Y also decreases. |