703_FINAL_study_guide.pdf - Econ 703 Final Study Guide...

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Econ 703 Final Study Guide Professor: Cathy Xue 1 Introduction 1.1 Population vs. Sample A population is simply a set of people, places, companies, things etc. that we are interested in. A sample is a subset of a population. You get data from this subset (or portion) of the population to form a dataset and do analysis. a census is a data set that covers an entire population, not just some of the observations. 1.2 Descriptive Statistics vs. Statistical Inference If we have a sample, or a census, and only want to describe the observations in that specific data set, then the statistics we estimate are called descriptive statistics . If we have a sample and want to say something about the population. This is called inferential statistics or statistical inference or inference . 1.3 Three Levels of Data (Quantitatively) Nominal Level Data - Can be used for classification purposes only. Ordinal Level Data - Can be used for classification and also ranking/ordering. Interval Level Data - This data allows us to classify, and assign rank/order, quantify distances, and perform various kinds of calculations. Interval data is always numerical. Nominal level and ordinal level data are called qualitative data since we can’t do much math with them. Interval level data is called quantitative data . Mathematically, we can do most operations with them. 1.4 Three Types of Data (Structurally) Cross-Sectional : The data is collected at the same time and you only observe each unit once. Time Series : You observe only one unit, but you observe it at many different points in time. Panel Data : You observe multiple units, and you observe these units at multiple points in time. 1
Econ 703 Statistics Foundations Professor: Cathy Xue 2 Tables and Graphs 2.1 Tables Class Interval Midpoint Frequency Relative Frequency Cumulative Frequency 2.2 Graphs for Quantitative Data Histogram Stem and Leaf Plot Scatter Plot 2.3 Graphs for Qualitative Data Pie Chart Bar Chart 3 Descriptive Statistics 3.1 Center of a Distribution Mean - The average. μ denotes the population mean, ¯ x denotes the sample mean. ¯ x = 1 n n i =1 x i = 1 n ( x 1 + x 2 + · · · + x n ) Median - The middle observation when the observations are in ascending order. If there are even numbers of observations, median is the average of the two numbers that are in the middle.

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