LIR 832 SPRING 2007 Lecture 2 power point notes

LIR 832 SPRING 2007 Lecture 2 power point notes -...

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1 Univariate Statistics LIR 832 Class #2 January 16, 2007 Topics for Next Four Lectures Topics for Next Four Lectures z Fundamental Problem in Statistics: Learning about populations from samples z Describing Data Compactly: How we might describe data, why compactness matters. Measures of Central Tendency (what are they, when to use them) Measures of dispersion z Probability Distributions: As samples are hopefully random draws from populations, we need to understand the likelihood of drawing samples. This leads us to a review of some basic probability distributions. z Inference from Samples to Populations: Sampling Distributions and the Central Limit Theorem Estimation Hypothesis Testing Basic Issues in Statistics Basic Issues in Statistics z Populations and Samples: Generally wish to know about populations What is a population? How do we count a population? What types of populations would you be concerned with in your professional life?
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2 Basic Issues in Statistics z Use of Samples to Learn about Populations z What is a sample? representative sample random sample convenience sample z Why use samples rather than populations? less time consuming to collect less expensive to collect often more accurate than census population may not exist at the time data is collected Basic Issues in Statistics Basic Issues in Statistics z Samples are affected by randomness , two samples drawn from a population are unlikely to be identical ( sampling variability ) and neither is an exact reproduction of the population. What is meant by random ? z An event is random if, despite knowing all of the possible outcomes in advance, we are not able to exactly predict a particular outcome. z experiment: M&M issue z Samples are, to some degree, random different samples produce different estimates sample mean may be different than (but close to) population mean Basic Issues in Statistics Basic Issues in Statistics z Since sample is not an exact reproduction of the population, we need to allow for sampling variability in using samples to tell us about populations. z What types of HR/IR issues might involve the use of samples?
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3 Example: Training Program Example: Training Program z We are interested in a training program which is supposed to improve productivity. It would be very expensive to implement throughout a firm, particularly if it doesn’t work. Instead, we set up an experiment in which we try the program on a sample of employees at a single location (this may be called a pilot program). Example: Training Program Example: Training Program z We experiment with a pilot program and find that productivity rose by 2% Our problem in using the pilot (sample): if we replicate the pilot throughout the firm is it reasonable to believe that: we will get a 2% boost in productivity, or This could this just be the result of getting a “good” sample (Folks who happened to respond favorably to the program).
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