STATISTICS for the Utterly Confused , 2 nd ed. SLIDES PREPARED By Lloyd R. Jaisingh Ph.D. Morehead State University Morehead KY Part 1 DESCRIPTIVE STATISTICS Chapter 1 Graphical Displays of Univariate Data Outline Do I Need to Read This Chapter?

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SLIDES PREPARED By Lloyd R. Jaisingh Ph.D. Morehead State University Morehead KY

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Outline • Do I Need to Read This Chapter? • 1-1 Introduction • 1-2 Frequency Distributions • 1-3 Dot Plots • 1-4 Bar Charts or Bar Graphs • 1-5 Histograms

Outline • 1-6 Frequency Polygons • 1-7 Stem-and-Leaf Displays or Plots • 1-8 Time Series Graphs • 1-9 Pie Graphs or Pie Charts • 1-10 Pareto Charts • It’s a Wrap

Objectives • Introduction of some basic statistical terms. • Introduction of some graphical displays.

Introduction • What is statistics?Statistics is the science of collecting, organizing, summarizing, analyzing, and makinginferences from data. • The subject of statistics is divided into two broad areas—descriptive statistics and inferential statistics.

Breakdown of the subject of statistics Statistics Descriptive Statistics Inferential Statistics • Includes • Making inferences • Hypothesis testing • Determining relationships • Making predictions • Includes • Collecting • Organizing • Summarizing • Presenting data

Introduction (contd.) • Explanation of the termdata: Data are the values or measurements that variables describing an event can assume. • Variables whose values are determined by chance are called random variables. • Types of variables – there are two types: qualitative and quantitative.

Introduction (contd.) • What are qualitative variables: These are variables that are nonnumeric in nature. • What are quantitative variables: These are variables that can assume numeric values. • Quantitative variables can be classified into two groups – discrete variables and continuous variables.

Introduction (contd.) • What are quantitative data:These are data values that are numeric. • Example: the heights of female basketball players. • What are qualitative data:These aredata values that can be placed into distinct categories according to some characteristic or attribute. • Example: the eye color of female basketball players.

Introduction (contd.) • What are discrete variables:These are variables that can assume values that can be counted. • Example: the number of days it rained in your neighborhood for the month of March. • What are continuous variables:These are variables that can assume all values between any two values. • Example: the time it takes to complete a quiz.

Introduction (contd.) • In order for statisticians to do any analysis, data must be collected or sampled. • We can sample the entire population or just a portion of the population. • What is a population? A population consists of all elements that are being studied. • What is a sample?: A sample is a subset of the population.

Introduction (contd.) • Example: If we are interested in studying the distribution of ACT math scores of freshmen at a college, then the population of ACT math scores will be the ACT math scores of all freshmen at that particular college. • Example: If we selected every tenth ACT math scores of freshmen at a college, then this selected set will represent a sample of ACT math scores for the freshmen at that particular college.

Introduction (contd.) Population – all freshmen ACT math scores Sample – every 10th ACT math score

Introduction (contd.) • What is a census?A census is a sample of the entire population. • Example: Every 10 years the U.S. government gathers information from the entire population. Since the entire population is sampled, this is referred to as a census.

Introduction (contd.) • Both populations and samples have characteristics that are associated with them. • These are called parameters and statistics respectively. • A parameter is a characteristic of or a fact about a population. • Example: The average age for the entire student population on a campus is an example of a parameter.

Introduction (contd.) • A statistic is a characteristic of or a fact about a sample. • Example: The average ACT math score for a sampleof students on a campus is an example of a statistic.

Introduction (contd.) Population – Described by Parameters Sample – Described by Statistics

1-2 Frequency Distributions • What is a frequency distribution?A frequency distribution is an organization of raw data in tabular form, using classes (or intervals) and frequencies. • What is a frequency count? The frequency or the frequency count for a data value is the number of times the value occurs in the data set.

Categorical or Qualitative Frequency Distributions • NOTE:We will consider categorical, ungrouped, and grouped frequency distributions. • What is a categorical frequency distribution?A categorical frequency distribution represents data that can be placed in specific categories, such as gender, hair color, political affiliation etc.

Categorical or Qualitative Frequency Distributions -- Example • Example: The blood types of 25 blood donors are given below. Summarize the data using a frequency distribution. AB B A O B O B O A O B O B B B A O AB AB O A B AB O A

Quantitative Frequency Distributions -- Ungrouped • What is an ungrouped frequency distribution?An ungrouped frequency distribution simply lists the data values with the corresponding frequency counts with which each value occurs.

Quantitative Frequency Distributions – Ungrouped -- Example • Example: The at-rest pulse rate for 16 athletes at a meet were 57, 57, 56, 57, 58, 56, 54, 64, 53, 54, 54, 55, 57, 55, 60, and 58. Summarize the information with an ungrouped frequency distribution.

Relative Frequency • NOTE: Sometimes frequency distributions are displayed with relative frequencies as well. • What is a relative frequency for a class?The relative frequency of any class is obtained dividing the frequency (f) for the class by the total number of observations (n).

Relative Frequency Example: The relative frequency for the ungrouped class of 57 will be 4/16 = 0.25.

Cumulative Frequency and Cumulative Relative Frequency • What is a cumulative frequency for a class?The cumulative frequency for a specific class in a frequency table is the sum of the frequencies for all values at or below the given class.

Cumulative Frequency and Cumulative Relative Frequency • What is a cumulative relative frequency for a class?The cumulative relative frequency for a specific class in a frequency table is the sum of the relative frequencies for all values at or below the given class.

Quantitative Frequency Distributions -- Grouped • What is a grouped frequency distribution?A grouped frequency distribution is obtained by constructing classes (or intervals) for the data, and then listing the corresponding number of values (frequency counts) in each interval.

Quantitative Frequency Distributions -- Grouped • There are several procedures that one can use to construct a grouped frequency distribution. • However, because of the many statistical software packages (MINITAB, SPSS etc.) and graphing calculators (TI-83 etc.) available today, it is not necessary to try to construct such distributions using pencil and paper.

Quantitative Frequency Distributions -- Grouped • Later, we will encounter a graphical display called the histogram. We will see that one can directly construct grouped frequency distributions from these displays.

Quantitative Frequency Distributions – Grouped -- Quick Tip • A frequency distribution should have a minimum of 5 classes and a maximum of 20 classes. • For small data sets, one can use between 5 and 10 classes. • For large data sets, one can use up to 20 classes.

Quantitative Frequency Distributions – Grouped -- Example • Example:The weights of 30 female students majoring in Physical Education on a college campus are as follows: 143, 113, 107, 151, 90, 139, 136, 126, 122, 127, 123, 137, 132, 121, 112, 132, 133, 121, 126, 104, 140, 138, 99, 134, 119, 112, 133, 104, 129, and 123. Summarize the data with a frequency distribution using seven classes.

Quantitative Frequency Distributions – Grouped -- Example Continued • What is a histogram?A histogram is a graphical display of a frequency or a relative frequency distribution that uses classes and vertical (horizontal) bars (rectangles) of various heights to represent the frequencies.

Quantitative Frequency Distributions – Grouped -- Example Continued • The MINITAB statistical software was used to generate the histogram. • The histogram has seven classes. • Classes for the weights are along the x-axis and frequencies are along the y-axis. • The number at the top of each rectangular box, represents the frequency for the class.

Quantitative Frequency Distributions – Grouped -- Example Continued • Observations • From the histogram, the classes (intervals) are 85 – 95, 95 – 105, 105 – 115 etc. with corresponding frequencies of 1, 3, 4, etc. • We will use this information to construct the group frequency distribution.

Quantitative Frequency Distributions – Grouped -- Example Continued • Observations (continued) • Observe that the upper class limit of 95 for the class 85 – 95 is listed as the lower class limit for the class 95 – 105. • Since the value of 95 cannot be included in both classes, we will use the convention that the upper class limit is not included in the class.

Quantitative Frequency Distributions – Grouped -- Example Continued • Observations (continued) • That is, the class 85 – 95 should be interpreted as having the values 85 and up to 95 but not including the value of 95. • Using these observations, the grouped frequency distribution is constructed from the histogram and is given on the next slide.

Quantitative Frequency Distributions – Grouped -- Example Continued • Observations (continued) • In the previous slide with the grouped frequency distribution, the sum of the relative frequencies did not add up to 1. This is due to rounding to four decimal places. • The same observation should be noted for the cumulative relative frequency column.

Dot Plots • What is a dot plot?A dot plot is a plot that displays a dot for each value in a data set along a number line. If there are multiple occurrences of a specific value, then the dots will be stacked vertically. • Example: The following frequency distribution shows the number of defectives observed by a quality control officer over a 30 day period. Construct a dot plot for the data.