week1 - Chapter 1: Section 1 What is Statistics? The...

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Chapter 1: Section 1 What is Statistics? The general field of Statistics involves methods for 1. Designing and carrying out research studies. 2. Describing collected data. 3. Making decisions, predictions, or inferences about phenomena represented by the data. Some Definitions Population: It is the entire collection of objects or outcomes about which information is sought. Sample: It is a subset of a population, containing the objects or outcomes that are actually observed. Ex 1. A physical education professor wants to study the physical fitness level of students at her university. There are 20,000 students in the university, and she draws a sample of size 100 to take a physical fitness test. The population of interest: 20,000 students in the university. The sample: the 100 students chosen to take the physical fitness test. 1
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Ex 2. A quality inspector samples 40 bolts from a large shipment and measures the length of each to see whether they meet a length specification. The population of interest: The entire shipment of bolts. The sample: 40 bolts actually inspected Ex 3 . On an election broadcast, a television network reports that 52% of the first 1,000 votes cast in California in the presidential contest for the Democratic candidate. Population of interest: Everyone in California who voted in the presidential contest. Sample: first 1000 votes cast. Types of Sampling Methods: 1) Simple Random Sample (SRS): A SRS of size n is a sample chosen by a method in which each collection of n population items is equally likely to comprise the sample. Ex 1.(contd) The PE professor obtains a list of all 20,000 students, numbered from 1 to 20,000. She uses a computer no. generator to generate 100 random integers between 1and 20,000. She invites the 100 students corresponding to those nos. to participate in the study. (SRS) 2
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Ex3(contd) Was the sample comprising of the first 1000 votes a SRS? How to draw a SRS from a population with N items? Use a random number generator Assign an integer between 1 and N to each item in the population. Generate a list of random integers between 1 and N . Choose the population items corresponding to those integers to get a SRS. In order to generate a list of random integers in Minitab, go to Calc>Random Data>Integer. Enter the number of random numbers you want to produce in the blank for “Generate ___ rows of data”. Enter 1 as the minimum value and N as the maximum value. Click O.K. 2) Sample of Convenience : A sample not drawn by a well-defined random method. e.g. A construction engineer received a shipment of 1000 concrete blocks, each weighing 50 pounds, in a huge pile. He wants to investigate the crushing strength of the blocks by measuring the strengths in a 3
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off the top of the pile as the sample. 4
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week1 - Chapter 1: Section 1 What is Statistics? The...

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