PSY200 Chapter 1/2

A stem-and-leaf plot offers an advantage over a histogram in that it shows the data both visually and numerically, whereas a histogram displays the data visually only.

True

True or False: In a negatively skewed distribution, the tail extends to the left.

True

True or False: Normal distributions are symmetric and inherently have no skew.

True

A sample in which every member of the population has an equal chance of being selected for inclusion in the study is a _____ sample.

random

Random assignment differs from random selection because:

random assignment deals with how participants in a sample are assigned to levels of the independent variable whereas random selection deals with how participants for a study are chosen to begin with.

The _____ is the difference between the lowest and highest score in the distribution.

range

Random selection is _____ used, but random assignment is _____ used.

rarely; frequently

To determine a person's percentile, first convert the person's _____ score to a z score.

raw

In the famous Zimbardo prison study, Stanford students were assigned the role of either a prisoner or a guard so that the experimenters could examine prison life behaviors and interactions. The experiment was intended to run for two weeks but was stopped after only six days because of the brutal behavior of the guards and the depression of the prisoners. What was the independent variable in this study?

role of prisoner or guard

When creating histograms and frequency polygons, the x-axis typically represents _____ and the y-axis represents _____.

values or intervals; frequencies

External validity is _____ by the use of volunteer samples.

weakened

In a sample of data that has several extremely high scores, creating positive skew, the mean:

will be greater than the median.

A _____ represents the number of standard deviations a particular score is from the mean average.

z score

The mean of the population is represented by the symbol _____ and the mean of the sample is represented by the symbol _____.

µ; M

In one statistics course, students reported studying an average of 9.92 hours a week, with a standard deviation of 4.54. Jessica is working two jobs and struggles to find time to study, averaging only 3 hours per week. What percent of students are at least as extreme as Jessica, in both directions? (Round z score to two decimal places.)

12.85

In one statistics course, students reported studying an average of 9.92 hours a week, with a standard deviation of 4.54. The professor tells David he scored at the 76th percentile. How many hours does he study per week? (Round z score to two decimal places.)

13.14

Here is a set of data: 11, 14, 10, 12, 19, 15, 18, 22, 14. What is the mode?

14

On the first statistics exam, the class average was 70 with a standard deviation of 6. Adam scored 82. What is his z score?

2.0

In one statistics course, students reported studying an average of 9.92 hours a week, with a standard deviation of 4.54. Treating this class as the population, what percent of students study more than 12 hours a week? (Round z score to two decimal places.)

32.28

Sixteen college freshmen were asked to record the number of alcoholic drinks that they typically consume in a week. Here are their data: 2, 4, 6, 0, 1, 10, 9, 0, 6, 3, 6, 8, 5, 4, 6, 2. What is the mean number of alcoholic drinks consumed per week?

4.5

What is the percentage of observations that fall between z scores of -1.2 and 0.50?

57.64

In a normal standard curve, approximately _____ percent of scores fall within 1 standard deviation from the mean.

68

Six students from a statistics class reported the number of hours of television they watched per week. Here are their data: 8, 10, 5, 14, 3, 6. What is the median number of hours of television watched per week for this sample of six students?

7.0

The mean for the population is 67 with a standard deviation of 8.78. Given a z score of 2.56, what is the raw score?

89.48

Here is a set of scores: 18, 99, 14, 16, 31, 43, 12, 14, 13, 51, 12. Which score is considered to be an outlier?

99

Dr. Choi is examining the weights of 750 children, 2 to 18 years old, to find out if childhood obesity rates are increasing in his city. With this type of data, is it better to use a frequency table or a grouped frequency table? Why?

A grouped frequency table is better because the data are a large set of continuous intervals.

Janice tosses a penny 10 times and finds that 7 of the 10 times the penny comes up heads and 3 of the 10 times the penny comes up tails. What should Janice conclude?

In the long-term the expected relative frequency would be 5/5, but with only 10 trials a different pattern has emerged.

Which score is more extreme: 0.32 or -0.45?

-0.45

Jenna scored 40 on a standardized test of reading ability where the mean score is 50 and the standard deviation is 10. Based on this information, what is Jenna's z score?

-1.0

Gibson (1986) asked a sample of college students to complete a self-esteem scale on which the midpoint of the scale was the score 108. He found that the average self-esteem score for this sample was 135.2, well above the actual midpoint of the scale. Given that the standard deviation of self-esteem scores was 28.15, what would be the z score for a person whose self-esteem score was 101.6?

-1.19

True or False: Raw data are scores that have been modified from their original form.

False

A community researcher wanted to explore the connection between the number of bathrooms in a house and the sale price of the house. He studied 1750 home sales in an economically diverse, medium-sized city and found that the average sale price went up by $63,000 for each full bath. Which statement involves a logical inferential statistic based on this research?

On average, adding a bathroom to your house can increase the sale price.

Why are true random samples rarely used?

Researchers rarely have access to the entire population.

Marco insists that women are poorer drivers than men. To back up his claim he describes two incidents: one in which his girlfriend sideswiped a car and a second in which his mother failed to react in time to avoid hitting a squirrel on the highway. Marco's attention to this positive evidence for his belief reflects:

a confirmation bias

A single observation can be expressed in a number of ways that all refer to that same observation and the exact same place within the normal curve. These expressions are:

a raw score, z score, and percentile.

A researcher wanted to determine whether eating sugary cereal for breakfast increased the aggression of second graders during their morning play period. After feeding a group of 20 students sugary cereal for breakfast she observed that, on average, the students committed 4.5 aggressive behaviors during their morning play period. In this example, the population is:

all second graders who eat sugary cereal for breakfast

The mean of the distribution of a set of z scores is:

always 0.

_____ are the requirements that the population from which one is sampling has specific characteristics that will allow one to make accurate inferences.

assumptions

A z score _____ the mean will always be _____.

below; negative

Dr. Feldman was interested in the effect of Valium on motor performance. He injected 30 rats in the experimental group with a small amount of Valium and 30 rats in the control group with saline solution. Following injection, he measured the rate of bar pressing by both groups of rats. On average, rats in the control group had 800 presses per hour and rats in the experimental group had 715 presses per hour. The same testing box was used for both groups of rats, but different student assistants tested the control and experimental groups. In this example, having two different student assistants test the two groups is a(n) _____ variable.

confounding

A researcher is interested in the eventual divorce rates of people who live together before they get married compared to those who do not cohabitate before marriage. The researcher is particularly interested in the couples who cohabitate to see if that leads to higher divorce rates. In a sense, the couples who do not cohabitate are serving as the _____ group.

control

A researcher is interested in comparing reaction time differences between men and women. He obtains a sample of 45 students from a psychology student research database. Participants take part in the study, the data are later analyzed, and the researcher concludes that women have faster reaction times compared to men. What type of sampling strategy was used in this study?

convenience

One rejects the null hypothesis when the test statistic falls in which area of the distribution?

critical region

Which "branch" of statistics uses numerical observations and incorporates them into an organized and informative summary of the data?

descriptive

Continuous observations are related to scale variables as ________ observations are related to nominal and ordinal variable(s).

discrete

The expected outcome if an experiment is repeated many, many times is the:

expected relative-frequency probability.

When a variable cannot take on values below a certain level, this is known as a(n)__effect.

floor

Any raw score can be converted into a z score, as long as you know the _____ and _____ of the distribution.

mean; standard deviation

A person's political affiliation is a(n) _____ variable.

nominal

The _____ curve forms a symmetrical and mathematically defined bell-shaped pattern.

normal

In a student election, five people run for student body president. The votes are tallied to create a list of candidates from most to least popular. The number of votes is then removed so that a list of candidates from most to least popular is presented. This is a(n) _____ variable.

ordinal

There are three different types of Olympic medals: gold, silver, and bronze. Which variable describes the different types of Olympic medals?

ordinal

In a physical geography course, the average score on the first exam across all sections of the course was 77.63 percent. Because all students were included in the calculation, the mean is assumed to be based on population data. The test average may be considered to be a:

parameter

The EPA noticed a large increase in the output of greenhouse gases from automobile traffic between 1996 and 1998 in California. When the agency looked at the data by city, it noticed that the score for Los Angeles was significantly higher than that for the other major cities in California combined. How was the city skewing the distribution?

positively

The distribution of National League baseball players' incomes is likely to be__skewed.

positively

Numbers that describe samples are called:

statistics

What type of graph displays individual data points of one variable both numerically and visually?

stem-and-leaf plot

Because of the principle of _____, when sample sizes are at least 30, the distribution will most likely resemble a normal distribution.

the central limit theorem

The concept of variability is best described as:

the spread of the distribution of data.

Matthew is interested in measuring whether there is a difference in time spent sleeping at night in a given week between elementary school-aged children and high school-aged students. In this study, the dependent variable is MOST likely to be:

time spent sleeping