Psych stats exam 2

If a population with μ = 0 and σ = 1.5 is transformed into z-scores, then the distribution of z-scores will have a mean of ___ and a standard deviation of ___.

0 and 1

A normal distribution has a mean of μ = 40 with σ = 10. What proportion of the scores in this distribution are smaller than X = 30?

0.1587

What proportion of a normal distribution falls between z = -1.96 and z = +1.96?

0.9500

One sample with n=8 scores has a mean of M=12, and a second sample with n=4 scores has a mean of M=8. If the two samples are combined, what is the mean for the combined set of scores?

10.7

Assuming that the null hypothesis is true, what is the probability of obtaining a sample that generates a z-value at least as extreme as z = -1.19?

234

A sample of n=800 scores has SS=50. If these same exact scores constituted a population with an N=800, then the SS value for the population would be?

50

John drives to work each morning and the trip takes an average of μ = 25 minutes. The distribution of driving times is normal with a standard deviation of σ = 10 minutes. For a randomly selected morning, what is the probability (in percentages) that John's drive to work will take no more than 40 minutes but will take more than 36 minutes?

6.89%

For a sample with M = 75 and s = 24, what is the X value corresponding to z = -0.25?

69

Which of the following statements cannot be true for a distribution of scores?

80% of the scores are above the median.

Assuming that the null hypothesis is true, what is the likelihood of obtaining a sample mean as least as extreme as one that produces a z-score of 2.58?

98%

A study investigates whether men or women (age 16-20) spend more money on clothing. Assume the amount of money spent is not normally distributed. Which statistical test should be used to analyze the data?

A Wilcoxon rank-sum test

A study investigates the frequency of drug use in suburban versus urban high schools.Which statistical test should be used to analyze the data?

A chi-square test of independence

When frequency data are collected, which test is used to determine how well an observed frequency distribution of two nominal variables fits some expected breakdown.

A chi-square test of independence

It is impossible for fewer than half of the scores in a distribution to have values greater than the mean.

False

True or False:A score with a value higher than the mean will have a negative z-score.

False

In right-skewed distributions the mean and the median are

Greater than the mode

If two samples are selected from the same population and are testing the same null hypothesis, under what circumstances will the two samples have exactly the same t statistic?

If the samples are the same size, have the same sample mean, and have the same sample variance.

In a population of N=60, 59 individuals all have scores that are exactly 1 point above the mean. From this information, what can you determine about the score for the sixtieth individual?

It is below the mean by 59 points.

A researcher calculated a t-ratio of 2.456, using a sample of 31 subjects. Estimate the p-value.

Lower than 4% but greater than 2%

A test statistic of t(10) = 2.5 was calculated. Estimate the p-value

Lower than 4%, greater than 2%

Chi-square tests use ____ data, whereas Wilcoxon tests use _______ data.

Nominal / Ordinal

In a distribution with negative skew, scores with the highest frequencies are ?

On the right side of the distribution

Which of the following accurately describes the critical region?

Outcomes with very low probabilities if the null hypothesis is true

The effect size for a chi-square test is determined by using the:

Phi-coefficient

Inferential statistics allow us to infer something about the ____based on the _______.

Population;Sample

The sampling distribution is a distribution of:

Sample means

A sample of n=225 scores has M=25 and s^2=64. What is the sample standard deviation?

Square root 64

The calculation of the standard deviation differs from the calculation of the average deviation in that the deviation scores are:

Squared

The standard deviation of the sampling distribution of mean differences between dependent samples in a two-group experiment is the:

Standard error of the difference scores.

Parametric is to nonparametric as _______is to______.

T-test;X^2 test

As the number of samples contained within a sampling distribution approaches infinity, the ...

The average of the sample means approaches the population mean and the sampling distribution approaches normality

What happens to the critical value for a chi-square test if the number of categories is increased?

The critical value also increases.

What happens to the critical value for a chi-square test if the size of the sample is increased?

The critical value depends on the number of categories, not the sample size.

When using a one-tailed hypothesis, the researcher predicts:

The direction of the expected difference between the groups

True or False: For a hypothesis test using a t statistic, the boundaries for the critical region will change if the sample size is changed. (Assume that the alpha level is held constant).

True

True or False: In general, an increase in the sample variance makes it less likely that the tstatistic will be large enough to reject the null hypothesis.

True

True or False: In general, the larger the value of the estimated standard error, the lower the likelihood of rejecting the null hypothesis.

True

True or False: Within any normal or symmetrical distribution of scores, the location specified by z = +.1 and the location specified by z = -.1 are exactly the same distance from the mean.

True

Assuming that a treatment has an effect on the population, it is still possible to obtain a sample mean that doesn't result in rejection of the null hypothesis. What can be concluded from this outcome?

Type 2 error

A normal distribution has a mean of μ = 24 with σ = 5.5. What is the minimum score needed to avoid being in the bottom 14% of the distribution?

X = >18.06

If researchers reported that, for a paired t-test t(15) = 2.57, p < 0.05, you can conclude that:

a total of 16 people participated in the study

The Wilcoxon rank-sum test is used with ________ data.

ordinal

For a normal population with a mean of μ = 80 and a standard deviation of σ = 10, what is the probability of obtaining a sample mean greater than M = 75 for a sample of n = 25 scores?

p = 0.9938

You are instructed to add 10 points to each score, square the resulting value, and find the sum of the squared numbers. How would this set of instructions be expressed in summation notation?

(X+10)^2

The sum of differences of each value from the mean of values in a distribution is always:

0

The Cohen's d effect size for the difference in means was 0.42. Does this suggest the difference is:

A small effect

A researcher is interested in studying if there are gender differences in risk-taking. She recruits 8 male and 9 female students to take a risk-taking survey. The survey is out of 20, with 20 being the highest risk-taking score. The males scored 15, 16, 19, 8, 19, 14, 16, 11. The females scored 15, 13, 11, 10, 8, 5, 12, 18, 10. Which test should be used to analyze these data?

A two-tailed independent t-test

If a treatment has a very small, but nevertheless legitimate effect on the population, then what is the most likely outcome for a small sample hypothesis test evaluating the treatment?

A type 2 error

The relationship between a statistic and a parameter is roughly equivalent to the relationship between...?

A typical UT class and all UT students

A study investigates whether men or women (age 16-20) spend more money on clothing. Assume the amount of money spent is normally distributed. Which statistical test should be used to analyze the data?

An independent t-test

What must be calculated to compute the critical value of t ?

Degrees of freedom

A researcher believes that a greater percentage of people in his art class are left-handed than the national average of 12%. He samples 60 students and finds 19 are left handed. What test should he use to analyze these data to test his hypothesis?

Chi-squared goodness of fit test

Which of the following is a inferential statistic used for measuring effect size in t-tests?

Cohen's d

If it is theoretically possible to divide the existing categories of a variable into an infinite number of values, then it is an example of a ________variable.

Continuous

Which of the following accurately describes the effect of increasing the sample size?

Decreases the standard error, increases statistical power, and has no effect on the risk of a type 1 error

The value of one score in a distribution is changed from X=20 to X=30. Which measures of central tendency is certain to be changed?

The mean

Which of the following is an assumption of χ2tests?

The sample should be randomly selected.

Which of the following is an assumption of the t-test ?

The sample size is typically less than 30.

Why does the critical value of t change when the sample size changes?

The t-distribution is different for different sample sizes.

Adding a new score to a distribution will not change the value of the mean, as long as the new score has the same value as the mean.

True

As sample size decreases, the estimated standard error increases.

True

For a positively skewed distribution, the mean usually has a larger value than either the median or the mode.

True

It is possible for the value of the mode to be greater than the value of the mean.

True

True or False: As df increases,the student'st distribution approaches a normal distribution.

True

In a study of the effects of caffeine on driving performance, researchers predict that those in the group that is given more caffeine will exhibit worse driving performance. The researchers are using a _______ hypothesis.

both directional and one-tailed

In general, decreasing the alpha level (for example, from .05 to .01) will ________.

decrease the likelihood of rejecting H0 and decrease the risk of a Type I error

In general, increasing the sample size (for example, from n = 4 to n = 50) will ________ the risk of Type-I error (assuming α is held constant at .05).

have no influence on

A researcher expects a treatment to produce a decrease in the population mean. The treatment is evaluated using a one tailed hypothesis test, and the test produces z = +1.85. Based on this result, what is the correct statistical decision?

he researcher should fail to reject H0 with either α = .05 or α = .01.

With α = .01 and df = 25, the critical value for a one-tailed t test is t = 2.485. Assuming all other factors are held constant, if the df value were decreased, the critical value of t would _______.

increase

A researcher is predicting that a treatment will decrease scores. If this treatment is evaluated using a directional hypothesis test, then the critical region for the test _______.

is in the left - hand tail of the distribution

With α = .10, the two-tailed critical region for a t test using a sample of n = 36 subjects will have boundaries of ______.

t = ±1.684

What z-score value separates the bottom 10% of a normal distribution from the top 90%?

z = -1.28

The calculation of the degrees of freedom for the ____________ is (r-1)(c-1).

χ2 test of independence