Chapter 2 - Review Questions Flashcards
What are the symbols of frequency and total scores?
The frequency of a score is symbolized. The total number of scores in the data is symbolized by N.
.
What do these symbols mean? N?
Is the number of scores in a sample.
What do these symbols mean? f?
Ss the frequency of a score or scores.
What is the difference between a bar graph and a histogram?
In a bar graph adjacent bars do not touch; in a histogram they do.
With what kind of data is each used?
Bar graphs are used with nominal or ordinal scores; histograms are used with interval or ratio scores.
a) What does it mean when a score is in a tail of a normal distribution? (b) What is the difference
between scores in the left-hand tail and scores in the right-hand tail?
What is the difference between a score’s simple frequency and its relative frequency?
Simple frequency is the number of times a score occurs; relative frequency is the proportion of time the score occurs.
What is the difference between a score’s cumulative frequency and its percentile?
Cumulative frequency is the number of scores at or below a particular score; percentile is usually defined as the percent of the scores below a particular score.
(a) What is the advantage of computing relative frequency instead of simple frequency? (b) What is the advantage of computing percentile instead of cumulative frequency?
What is the difference between the polygon for a skewed distribution and the polygon for a normal distribution?
A skewed distribution has one distinct tail; a normal distribution has two.
What is the difference between the polygon for a bimodal distribution and the polygon for a normal distribution?
A bimodal distribution has two distinct humps above the two highest-frequency scores; a normal distribution has one hump and one highest-frequency score.
What is the difference between the graphs for a negatively skewed distribution and a positively skewed distribution?
In reading psychological research, you encounter the following statements. Interpret each one. (a) “The IQ scores were approximately normally distributed.” (b) “A bimodal distribution of physical agility scores was observed.” (c) “The distribution of the patients’ memory scores was severely negatively skewed.”
What is the difference between how we use the proportion of the total area under the normal curve to determine relative frequency and how we use it to determine percentile?
For relative frequency, we find the proportion of the total area under the curve at the specified scores. For percentile, we find the proportion of the total area under the curve that is to the left of a particular score.
What type of frequency graph is appropriate when counting the number of: Blondes, brunettes, redheads, or “others” attending a college?
Bar Graph
What type of frequency graph is appropriate when counting the number of: People having each body weight reported in a statewide survey?
Polygon
What type of frequency graph is appropriate when counting the number of: Children in each grade at an elementary school? and
Bar Graph
What type of frequency graph is appropriate when counting the number of: Car owners reporting above-average, average, or below-average problems with their car?
Histogram
The distribution of scores on a statistics test is positively skewed. What does this indicate about the difficulty of the test?
The distribution of salaries at a large corporation is negatively skewed. What would this indicate about the pay at this company?
The most frequent salaries tend to be in the middle to high range, with relatively few extremely low salaries.
The distribution of salaries at a large corporation is negatively skewed. If your salary is in the tail of this distribution, what should you conclude about your salary?
Yours is one of the lowest, least common salaries.
(a) On a normal distribution of exam scores, Crystal scored at the 10th percentile, so she claims that she outperformed 90% of her class. Why is she correct or incorrect? (b) Ernesto’s score is in a tail of the normal curve, so he claims to have one of the highest scores. Why is he correct or incorrect?
Interpret each of the following. You scored at the 35th percentile.
35% of the sample scored below you.
Interpret each of the following. Your score has a relative frequency of .40.
Your score occurred 40% of the time.
Interpret each of the following. Your score is in the upper tail of the normal curve.
It is one of the highest and least frequent scores.
Interpret each of the following. Your score is in the left-hand tail of the normal curve.
It is one of the lowest and least frequent scores.
Interpret each of the following. The cumulative frequency of your score is 50.
50 participants had either this score or a score below it.
Interpret each of the following. Using the area under the normal curve, your score is at the 60th percentile.
60% of the area under the curve is to the left of (below) your score.
Draw a normal curve and identify the approximate location of the following scores. (a) You have the most frequent score. (b) You have a low-frequency score, but it is higher than most. (c) You have one of the lower scores, but it has a relatively high frequency. (d) Your score seldom occurred.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. Order the scores 45, 60, 70, 72, and 85 from most frequent to least frequent.
70, 72, 60, 85, 45.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. What is the percentile of a score of 60?
Because .20 of the area under the curve is to the left of 60, it’s at the 20th percentile.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. What proportion of the sample scored below 70?
With .50 of the area under the curve to the left of 70, .50 of the sample is below 70.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. What proportion scored between 60 and 70?
With .50 of the area under the curve below 70, and .20 of the area under the curve below 60, then .50-.20=.30 of the area under the curve is between 60 and 70.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. What proportion scored above 80?
.20.
The following shows the distribution of final exam scores in a large introductory psychology class. The proportion of the total area under the curve is given for two segments. What is the percentile of a score of 80?
With .50 below 70 and .30 between 80 and 70, a total of .50+.30=.80 of the curve is below 80, so it is at the 80th percentile.
What type of graph should you create when counting the frequency of: The brands of cell phones owned by students? Why?
Bar graph; for a nominal (categorical) variable.
What type of graph should you create when counting the frequency of: The different body weights reported in a statewide survey? Why?
Polygon; for many different ratio scores.
What type of graph should you create when counting the frequency of: The people falling into one of eight salary ranges? Why?
Histogram; for only 8 different ratio scores.
What type of graph should you create when counting the frequency of: The number of students who were absent from a class either at the beginning, middle, or end of the semester? Why?
Bar graph; for an ordinal variable.
An experimenter studies vision in low light by having participants sit in a darkened room for either 5, 15, or 25 minutes and then testing their ability to correctly identify 20 objects. (a) What is the independent variable here? (b) What are the conditions? (c) What is the dependent variable? (d) You would use the scores from which variable to create a frequency distribution?
Why do we create a bar graph with a nominal or ordinal X variable?
These variables are assumed to be discrete, and the spaces between bars communicate a discrete variable.
Why do we connect data points with straight lines with an interval or ratio X variable?
These variables are assumed to be continuous, and the lines between data points communicate that the variable continues between the plotted X scores.
