PSYC 210 Poll Questions

Using n instead of n-1 in the formula for sample variance results in _____ estimator of the population variance and systematically ______

-biased -underestimates it

Suppose the correlation between X1 & Y is r = .40. When a second variable (X2) is added to the regression equation, we obtain R-square = 0.60. What additional proportion of the Y score variance is added by using both variables compared to using X1 alone?

.44; take the difference between the 2 r-squared values (.6-.16)

For the regression equation Yhat=3X-2, if the mean for Y is 10, what is the mean for X?

4 (just plug in 10 for Y)

Suppose a normal distribution has a mean of 8 and a standard deviation of 2. What is the range of scores within which at least 95% of scores are contained? A. 8 to 10 B. 4 to 12 C. 6 to 10 D. 6 to 8

4 to 12

As a general rule, when the number of intervals needed to summarize a data set is smaller than ___, we can leave the data ungrouped. A. 5 B. 15 C. 20 D. The data should never be grouped.

5

Suppose the average score on a test is 500 with a sd of 100. if each score is increased by 25, what are the new mean and sd?

525, 100

use the empirical rule to find percent of data that is within one standard deviation of the mean

68%

For a population with a standard deviation of 10, a score of X = 60 corresponds to a z = -1.50. What is the population mean? A. 30 B. 45 C. 75 D. 90

75

What is the IQR for the following data: 6, 3, 14, 1

8

A statistical procedure used to compute the slope (b) and y-intercept (a) of the best-fitting line to a set of data points is called: A. the method of least squares B. the method of most squares C. the method of common squares D. the method of data squares

A

To accommodate more predictor variables in the equation of a regression line, we add the ___ and the ___ to the equation of the regression line for each additional variable. A. slope; predictor variable B. criterion variable; predictor variable C. coefficient of determination; sample size D. slope; coefficient of determination

A

When a Pearson correlation is computed for data measured on an ordinal scale (ranks), the result is known as A. the Spearman correlation. B. the point-biserial correlation. C. the phi coefficient. D. It is still called a Pearson correlation.

A. The Spearman correlation

The mean is used to describe: A. data that are normally distributed B. data that are on an interval scale C. data that are on a ratio scale D. all of the above

All of the above

The median is: A. the preferred measure of central tendency when outliers are in a data set. B. the middle value in a distribution of 123 scores listed in numerical order. C. at the 50th percentile of a cumulative percent distribution. D. all of the above.

All of the above

For a population with a standard deviation of 6, what is the z-score corresponding to a score that is 12 points above the mean? A. z = 1 B. z = 2 C. z = 6 D. z = 12

B

For the regression equation, ŷ = -2x + 6, what can be determined about the correlation between x and y? A. The correlation definitely will be positive. B. The correlation definitely will be negative. C. The correlation will be relatively large and positive. D. The correlation will be relatively large and negative.

B

Without doing any calculations, which of the following samples has the largest variance? A. 1, 3, 4, 5, 6 B. 1, 5, 8, 12, 22 C. 30, 32, 34, 35, 36

B

For which of the following Pearson correlations would the data points be clustered mostly around a straight line? A. r = -0.10 B. r = +0.40 C. r = -0.70 D. there is no relationship between the correlation and how close the points are to a straight line.

C

If you have a score of X = 75 on an exam, which set of parameters would give you the highest position within the class? A. mean of 70, standard deviation of 5 B. mean of 70, standard deviation of 10 C. mean of 60, standard deviation of 5 D. mean of 60, standard deviation of 10

C

Outliers can obscure the relationship between two factors by altering the: A. extent to which two correlations are related to a third factor B. the extent to which changes in one factor cause changes in a second factor C. direction and strength of an observed correlation coefficient D. none of the above

C

Which of the following is true of the mean? A. Changing the value of one score will always change the value of the mean. B. Adding a score to a distribution will always change the value of the mean. C. Removing a score from a distribution will always change the value of the mean. D. All three (a-c) are correct. E. None of the above are correct.

Changing the value of one score will ALWAYS change the value of the mean

A researcher measures the following correlation between the amount of fat consumed in a diet and general health: r = -0.62. Which of the following gives an appropriate description of the relationship between these two factors? A. Increased amount of fat in diet was negatively associated with general health, such that people who consumed more fat in their diet had lower general health. B. About 38%, of the variability in general health can be explained by the amount fat consumed in a diet. C. Increasing the amount of fat consumed in a diet leads to a decline in general health. D. both a and b

D

For an exam with a mean of M = 74 and a standard deviation of s = 8, Mindy has a score of X = 80, Tosh's score corresponds to z = +1.50, and Sarah's score is located above the mean by 10 points. If the students are placed in order from smallest score to largest score, what is the correct order? A. Tosh, Mindy, Sarah B. Sarah, Tosh, Mindy C. Mindy, Tosh, Sarah D. Mindy, Sarah, Tosh

D

A researcher summarizes a set of data by describing the score that occurred most often. What type of statistics did the researcher use to summarize these data? A. descriptive B. inferential C. analytical D. professional

Descriptive

The research method used to demonstrate that one variable causes changes in a dependent variable is called the: A. experimental method B. quasi-experimental method C. correlational method D. investigative method

Experimental Method

T/F: A trimodal distribution must be symmetrical

False

T/F: Adding a score to a data set will change the mean

False. If you add a score that is equal to the mean, the mean will not change

True/False: The mode is always located at the exact center of a perfectly symmetrical distribution

False. be careful about the word ALWAYS; could be bimodal!!

X=enjoyment of statistics class. Y=life happiness. b=2. The best interpretation of b in this model is:

For every additional point of enjoyment of statistics class, there is a 2 point increase in life happiness

What does a higher beta value mean?

It means that that predictor has a bigger impact on the criterion

The ______ is the preferred measure of central tendency when there are outliers or the data is heavily skewed

Median

What measure of central tendency is most resistant to extreme values?

Median

Suppose you have some skewed grade data. Which would you like to see?

Negative/Left Skewed data

A researcher measures the following scores: 0, 2, 2, 2, 2,2, 2, 2, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0, 2, 4, 2, 2, 4, 4, 4, 4, 4, 4, and 0. Should these data be grouped? A. yes, because so many scores were measured B. yes, because the range of values is small C. no, because the data are categorical D. no, because the number of different score is small

No, because the number of different scores is small

What is the value of SS for the following set of scores? Scores: 5, 6, 1. A. 62 B. 13 C. 6 D. None of the other choices are correct.

None of the other choices are correct

When I say that the mean is considered the balance point of a distribution, I'm saying that it is: A. always equal to 0 B. not always located at the center of a distribution of scores C. equal to the score in the middle of a distribution of scores D. used to measure the extent to which objects balance

Not always located at the center of a distribution of scores

A researcher records the family relationship (brother, son, father, cousin, etc.) of the people who stay in regular contact with loved ones in a nursing home. What type of measure is family relationship? A. quantitative and discrete B. qualitative and discrete C. qualitative and continuous D. quantitative and continuous

Qualitative and Discrete

A researcher records the number of times a person repeats a compulsive behavior. What type of data was measured? A. qualitative B. quantitative C. nominal D. ordinal

Quantitative

What measure of variability would you choose for the bell tower data

Standard deviation, variance, IQR, range

a distribution has many more scores above the mean than below the mean. What can be said about the distribution?

The distribution is probably negatively skewed

The regression equation is determined by minimizing

The total squared error between the predicted y values and the actual y values

T/F: Outliers can impact the range more than the IQR

True

T/F: Changing a score in a data set will change the mean

True!!!

If there is a negative correlation between X and Y, then the regression equation will have

a b value that is less than 0; negative slope=negative correlation; the b value tells you the slope

What values are added to the new regression equation when a new predictor variable is added to the model

an additional b and X

An interval scale A. has no true zero B. is distributed on an equidistant scale C. is the most informative scale of measurement D. both a and b

both a and b; remember that an interval scale is like a likert scale

True/False: The mean is always at the 50th percentile

false. when the data is skewed, the mean is not always going to be at the 50th percentile

Adding 2 feet to everyone's bell tower estimate will

increase the mean by 2

Mean is 1000 and sd is 100. offers 10% discount. what are the new mean and sd?

mean=900 and sd=90

A researcher measures the number of hours spent studying among students living on-campus and off-campus at a local college. In this study, location (on-campus, off-campus) is the ___ and hours spent studying is the ___. A. independent variable; dependent variable B. dependent variable; independent variable C. quasi-independent variable; dependent variable D. dependent variable; quasi-independent variable

quasi-independent variable; dependent variable

A researcher selects a ___ and uses inferential statistics to draw conclusions about the larger ___. A. sample; statistic B. parameter; population C. population; sample D. sample; population

sample; population

A researcher conducts an experiment to determine whether moderate doses of St. Johns Wort have any effect of memory for college students. For this study, what is the independent variable? A. the amount of St. Johns Wort given to each participant B. the memory score for each participant C. the group of college students D. cannot answer without more information

the amount of St. Johns Wort given to each participant

A professor records the academic major for each student in a class of n = 40. The best measure of central tendency for these data would be ____. A. the mean B. the median C. the mode D. Central tendency cannot be determined for these data.

the mode

The criterion in a regression is

the predicted y value

set of n=15. correlation of r=.4. if each x value is multiplied by 2, what value will be obtained for new correlation?

the slope will be changed but not the actual relationship

The sample variance is a(n) ____ when, on average, its value is equal to the value of the population variance. A. biased estimator B. unbiased estimator

unbiased estimator

Which of the following factors is NOT important to consider when interpreting a correlation coefficient

unit of measurement because you have converted your x and y values to z scores