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Unit 4 Part B Concept: Frequencies EQ: How do we record and use various types of frequencies? Vocabulary: Joint Frequency Marginal Frequency Trend Conditional Relative Frequency 4.2.1: Summarizing Data Using Two- Way Frequency Tables 1

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Standard…. S.ID.5 Summarize categorical data for two categories in twoway frequency tables. Interpret relative frequencies in the context of the data (including joint, marginal, and conditional relative frequencies). Recognize possible associations and trends in the data. 4.2.1: Summarizing Data Using Two- Way Frequency Tables 2

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Introduction Information about people who are surveyed can be captured in two-way frequency tables. A two-way frequency table is a table of data that separates responses by a characteristic of the respondents. 4 4.2.1: Summarizing Data Using Two-Way Frequency Tables Type of characteristic Type of response Response 1Response 2 Characteristic 1ab cd

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Introduction, continued A joint frequency is the number of responses for a given characteristic. The entries in the cells of a two-way frequency table are joint frequencies. In the sample table, a, b, c, and d are each joint frequencies. A marginal frequency is the total number of times a response was given, or the total number of respondents with a given characteristic. This is the sum of either a row or a column in a two-way frequency table. In the sample table, a + b would be the marginal frequency of people with Characteristic 1. 5 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Introduction, continued A conditional relative frequency allows a comparison to be made for multiple responses in a single row, single column, or table. Relative frequencies are expressed as a percentage, usually written as a decimal. In the sample table, is the relative frequency of Response 1 for people with Characteristic 1. 6 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Key Concepts A two-way frequency table divides survey responses by characteristics of respondents. The number of times a response was given by people with a certain characteristic is called a joint frequency. A marginal frequency is the total number of times a response is given, or the total number of people with a certain characteristic. 7 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Key Concepts, continued A conditional relative frequency expresses a number of responses as a percentage of the total number of respondents, the total number of people with a given characteristic, or the total number of times a specific response was given. Trends, or patterns of responses, can be identified by looking at the frequency of responses. 8 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice Example 1 Abigail surveys students in different grades, and asks each student which pet they prefer. The responses are in the table below. What is the marginal frequency of each type of pet? 9 4.2.1: Summarizing Data Using Two-Way Frequency Tables Grade Preferred pet BirdCatDogFish 93495322 107366410

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Guided Practice: Example 1, continued 1.Sum the responses of people with each characteristic for the first pet type, bird. 3 people in grade 9 preferred birds, and 7 people in grade 10 preferred birds. 3 + 7 = 10 people who preferred birds 10 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 1, continued 2.Sum the responses of people with each characteristic for the second pet type, cat. 49 people in grade 9 preferred cats, and 36 people in grade 10 preferred cats. 49 + 36 = 85 people who preferred cats 11 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 1, continued 3.Sum the responses of people with each characteristic for the third pet type, dog. 53 people in grade 9 preferred dogs, and 64 people in grade 10 preferred dogs. 53 + 64 = 117 people who preferred dogs 12 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 1, continued 4.Sum the responses of people with each characteristic for the fourth pet type, fish. 22 people in grade 9 preferred fish, and 10 people in grade 10 preferred fish. 22 + 10 = 32 people who preferred fish 13 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 1, continued 5.Organize the marginal frequencies in a two-way frequency table. Create a row and include the marginal frequencies of each response under the name of each response. 14 4.2.1: Summarizing Data Using Two-Way Frequency Tables Grade Preferred pet BirdCatDogFish 93495322 107366410 Total108511732

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4.2.1: Summarizing Data Using Two-Way Frequency Tables Guided Practice: Example 1, continued 15

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Guided Practice Example 2 Ms. Scanlon surveys her students about the time they spend studying. She creates a table showing the amount of time students studied and the score each students earned on a recent test. 16 4.2.1: Summarizing Data Using Two-Way Frequency Tables Time spent studying in hours Test score 0–2526–5051–7576–100 0–228122 2–4010824 4–61029 6+0014

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Guided Practice: Example 2, continued Ms. Scanlon wants to understand the distribution of scores among all the students, and to get a sense of how students are performing and how much students are studying. Find the conditional relative frequencies as a percentage of the total number of students. 17 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 2, continued 1.Find the total number of students represented in the table by summing the joint frequencies. 2 + 8 + 12 + 2 + 0 + 10 + 8 + 24 + 1 + 0 + 2 + 9 + 0 + 0 + 1 + 4 = 83 18 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 2, continued 2.Divide each joint frequency by the total number of students. 19 4.2.1: Summarizing Data Using Two-Way Frequency Tables

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Guided Practice: Example 2, continued 3.Represent the conditional joint frequencies in a new table. Insert each conditional joint frequency in a table set up the same way as the two-way frequency table. 20 4.2.1: Summarizing Data Using Two-Way Frequency Tables Time spent studying in hours Test score 0–2526–5051–7576–100 0–20.0240.0960.1450.024 2–400.1200.0960.289 4–60.01200.0240.108 6+000.0120.048

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4.2.1: Summarizing Data Using Two-Way Frequency Tables Guided Practice: Example 2, continued 21

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