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b.lect1

# b.lect1 - Outline Why Statistics Populations Samples and...

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Outline Why Statistics? Populations, Samples, and Census Some Sampling Concepts Lecture 1 Chapter 1: Basic Statistical Concepts M. George Akritas M. George Akritas Lecture 1 Chapter 1: Basic Statistical Concepts

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Outline Why Statistics? Populations, Samples, and Census Some Sampling Concepts Why Statistics? Populations, Samples, and Census Some Sampling Concepts Representative Samples Simple Random and Stratified Sampling Sampling With and Without Replacement Non-representative Sampling M. George Akritas Lecture 1 Chapter 1: Basic Statistical Concepts
Outline Why Statistics? Populations, Samples, and Census Some Sampling Concepts Example (Examples of Engineering/Scientific Studies) I Comparing the compressive strength of two or more cement mixtures. I Comparing the effectiveness of three cleaning products in removing four different types of stains. I Predicting failure time on the basis of stress applied. I Assessing the effectiveness of a new traffic regulatory measure in reducing the weekly rate of accidents. I Testing a manufacturer’s claim regarding a product’s quality. I Studying the relation between salary increases and employee productivity in a large corporation. What makes these studies challenging (and thus to require Statistics) is the inherent or intrinsic variability : M. George Akritas Lecture 1 Chapter 1: Basic Statistical Concepts

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Outline Why Statistics? Populations, Samples, and Census Some Sampling Concepts I The compressive strength of different preparations of the same cement mixture will differ. The figure in http://sites. stat.psu.edu/ ~ mga/401/fig/HistComprStrCement.pdf shows 32 compressive strength measurements, in MPa (MegaPascal units), of test cylinders 6 in. in diameter by 12 in. high, using water/cement ratio of 0.4, measured on the 28th day after they are made. I Under the same stress, two beams will fail at different times. I The proportion of defective items of a certain product will differ from batch to batch. Intrinsic variability renders the objectives of the case studies, as stated, ambiguous. M. George Akritas Lecture 1 Chapter 1: Basic Statistical Concepts
Outline Why Statistics? Populations, Samples, and Census Some Sampling Concepts The objectives of the case studies can be made precise if stated in terms of averages or means . I Comparing the average hardness of two different cement mixtures. I Predicting the average failure time on the basis of stress applied. I Estimation of the average coefficient of thermal expansion. I Estimation of the average proportion of defective items. Moreover, because of variability, the words ”average” and ”mean” have a technical meaning which can be made clear through the concepts of population and sample . M. George Akritas Lecture 1 Chapter 1: Basic Statistical Concepts

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Outline Why Statistics?
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b.lect1 - Outline Why Statistics Populations Samples and...

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