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29 Cards in this Set

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Descriptive Statistics are used for what?

to simplify and summarize data

Inferential Statistics are used for what?

to make general conclusions about populations




using sample data.

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.

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.

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

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

What additional information is obtained from measurements on a ratio scale compared to measurements on an interval scale?

the relative sizes of two measurements

A numerical value that describes a sample data set is called a

statistic

A numerical value that describes a population data set is called a

parameter

Why is it necessary to have more than one method for measuring central tendency?

Because no single method works well in all situations.

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

For a negatively skewed distribution with a mean of M=20, what is the most probable value for the median?

greater than 20

For a perfectly symmetrical distribution with a median of 30, what is the value of the mean?

30

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.

experimental?

manipulating 2 variables

nonexperimental?

observation

f?

frequency of X

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.

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.

SS

SS is the sum of squared deviation scores.

Variance

Variance is the mean squared deviation.

Standard deviation

Standard deviation is the square root of the variance. It provides a measure of the standard distance from the mean.

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.

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.

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.

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.

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.

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.

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.