Presentation on theme: "Section 2-2 Chapter 2 Frequency Distributions and Graphs"— Presentation transcript:
1 Section 2-2 Chapter 2 Frequency Distributions and Graphs Organizing Data
2 Frequency distribution - is the organization of raw data in table form, using classes and frequencies.Categorical frequency distribution - is used for data that can be placed in specific categories, such as nominal- or ordinal-level dataNominal data are categorical data where the order of the categories is arbitraryOrdinal data are categorical data where there is a logical ordering to the categories
3 A survey was taken on how much trust people place in Section 2-2 Exercise #7A survey was taken on how much trust people place inthe information they read on the Internet. Construct acategorical frequency distribution for the data.A = trust in everything they read,M = trust in most of what they read,H = trust in about half of what they read,S = trust in a small portion of whatthey read.MAHS
4 Constructing a Grouped Frequency Distribution Step 1 Determine the classes.Find the highest and lowest value.Find the range.Select the number of classes desired.Find the width by dividing the range by the number of classes and rounding up.Select a starting point (usually the lowest value or any convenient number lessthan the lowest value); add the width to get the lower limits.Find the upper class limits.Find the boundaries.Step 2 Tally the data.Step 3 Find the numerical frequencies from the tallies.Step 4 Find the cumulative frequencies.
5 Section 2-2 Exercise #11The average quantitative GRE scores for the top 30 graduate schools of engineering are listed below. Construct a frequency distribution with six classes.767770761760771768776756763747766754778762780750746764769759757753758
6 The ages of the signers of the Declaration of Section 2-2 Exercise #13The ages of the signers of the Declaration ofIndependence are shown below (age is approximatesince only the birth year appeared in the source, andone has been omitted since his birth year isunknown). Construct a frequencydistribution for the data usingseven classes.41544740393550374942703244523034694533636027383643484631556253
7 Section 2-3 Chapter 2 Frequency Distributions and Graphs Histograms, Frequency Polygons, and Ogives
8 The three most commonly used graphs in research are as follows: 1. The histogram.2. The frequency polygon.3. The cumulative frequency graph, or ogive (pronounced o-jive).
9 HistogramThe histogram is a graph that displays the data by using contiguous vertical bars (unless the frequency of a class is 0) of various heights to represent the frequencies of the classes.
10 Frequency PolygonThe frequency polygon is a graph that displays the data by using lines that connect points plotted for the frequencies at the midpoints of the classes. The frequencies are represented by the heights of the points.
11 OgiveThe ogive is a graph that represents the cumulative frequencies for the classes in a frequency distribution.
12 Constructing Statistical Graphs Step 1 Draw and label the x and y axes.Step 2 Choose a suitable scale for the frequencies or cumulative frequencies, and label it on the y axis.Step 3 Represent the class boundaries for the histogram or ogive, or the midpoint for the frequency polygon, on the x axis.Step 4 Plot the points and then draw the bars or lines.
13 For 108 randomly selected college applicants, the Section 2-3 Exercise #1For 108 randomly selected college applicants, thefollowing frequency distribution for entrance examscores was obtained. Construct a histogram,frequency polygon, and ogive for the data.Class limits126 – 134928117 – 12543108 – 1162299 – 107690 – 98Frequency
14 Section 2-3 Exercise #1Applicants who score above 107 need not enroll in a summer developmental program. In this group, how many students do not have to enroll in thedevelopmental program?
15 Section 2-3 Exercise #7The air quality measured for selected cities in the UnitedStates for 1993 and 2002 are shown. The data are thenumber of days per year that the cities failedto meet acceptable standards. Constructa histogram for both years and see if thereare any notable changes. If so, explain.
17 The number of calories per serving for selected ready - Section 2-3 Exercise #15The number of calories per serving for selected ready -to - eat cereals is listed here. Construct a frequencydistribution using seven classes. Draw ahistogram, frequency polygon, and ogive forthe data, using relative frequencies.Describe the shape of the histogram.1301901408010012022011021090200180260270160240115225
20 When the peak of a distribution is to the left and the data values taper off to the right, a distribution is said to be positively or right-skewed. See Figure 2–8(e).When the data values are clustered to the right and taper off to the left, a distribution is said to be negatively or left-skewed.Distributions with one peak, such as those shown in Figure 2–8(a), (e), and (f), are said to be unimodal. (The highest peak of a distribution indicates where the mode of the data values is. The mode is the data value that occurs more often than any other data value.)When a distribution has two peaks of the same height, it is said to be bimodal. See Figure 2–8(g).Finally, the graph shown in Figure 2–8(h) is a U-shaped distribution.