# MBA 611 STATISTICS AND QUANTITATIVE METHODS

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1 MBA 611 STATISTICS AND QUANTITATIVE METHODS Part I. Review of Basic Statistics (Chapters 1-11) A. Introduction (Chapter 1) Uncertainty: Decisions are often based on incomplete information from uncertain events. We use statistical methods and statistical analysis to make decisions in uncertain environment. Population: Sample: A population is the complete set of all items in which an investigator is interested. A sample is a subset of population values. & Eample: Population - High school students - Households in the U.S. Sample - A sample of 30 students - A Gallup poll of 1,000 consumers - Nielson Survey of TV rating Random Sample: A random sample of n data values is one selected from the population in such a way that every different sample of size n has an equal chance of selection. & Eample: Random Selection - Lotto numbers - Random numbers Random Variable: A variable takes different possible values for a given subject of study. Numerical Variable: A numerical variable takes some countable finite numbers or infinite numbers. Categorical Variable: A categorical variable takes values that belong to groups or categories. Data: Data are measured values of the variable. There are two types of data: quantitative data and qualitative data. 1

2 Quantitative Data: Qualitative Data: Quantitative data are data measured on a numerical scale. Qualitative data are non-numerical data that can only be classified into one of a group of categories. & Eample: 1. Temperature. Height 3. Age in years 3. Income 4. Prices 5. Occupations 6. Race 7. Sales and Advertising 8. Consumption and Income Statistics: Statistics is the science of data. This involves collecting, classifying, summarizing, analyzing data, and then making inferences and decisions based on the data collected. Population Parameters: The numerical measures of a population are called parameters. & Eample: Population average. Sample Statistics: The numerical measures of a sample are called sample statistics. & Eample: Sample average. Descriptive Statistics: Descriptive statistics involves collecting, classifying, and summarizing data. Inferential Statistics: Inferential statistics makes statistical inference about the population parameters based on sample information. Business Decisions: From time to time, we use quantitative analysis to make business decisions. & Eample: Economics: Price of a Good, Interest Rate, Mortgage Rate Finance: Returns, Stock Prices Marketing: Advertising, Sales Management: Quality Control

3 B. Descriptive Statistics (Chapters and 3) B.1 Describing Data Sets Graphically (Chapter ) The simplest way to describe data is to use graphs. The following shows two types of graphs: frequency histogram and line graph. B.1.1 Relative Frequency Histogram The relative frequency histogram shows the proportions of the total set of data values that fall in various numerical intervals. & Eample: Sale Prices The following data represent sale prices (in thousands of dollars) for a random sample of 5 residential properties sold Sort the data Organize the data and construct the following relative frequency distribution table. Class i Class Limits Freq. ( f i ) Relative Frequency 1 (30, 49) /5 =0.08 (50, 69) 7 7/5 = (70, 89) 8 8/5 = (90, 109) 5 5/5 = (110, 19) /5 = (130, 149) 1 1/5 = 0.04 Sum 5 1 3

4 The relative frequency histogram is Relative Frequency Relative Frequency Sale Price In this graph, 1. The data are classified into 6 classes.. Each class has the same width. The width is equal to The graph shows the midpoints of these classes on the horizontal ais. 4. The vertical bar shows the relative frequency of sale prices falling in each class interval. How to decide the class width: the largest number - the smallest number Width =. the number of classes & Eample: Sale Prices Width = = O Eercise: The following data are year-to-day (YTD) returns for a sample of 30 mutual funds ( ) Then Width = =

5 Sort the data as the following: Organize the data and construct the following relative frequency distribution table. Class i Class Limits Freq. ( f i ) Relative Frequency 1 (-5.00, -.51) (-.50, -0.01) Sum Draw a relative frequency histogram. Tetbook Eercises:.5,.6,.8,.9, pages -3. Ecel: Create a Histogram 1. Click on Tools.. Click on Data Analysis. (If Data Analysis is not on the list, click and Check AAnalysis to install the add-in from Microsoft Office CD.) 3. Select Histogram; click OK. 4. Complete dialog bo: Input range contains data; Bin range contains upper boundary of interval; click OK. 5. Delete (using Edit) last row called More. 5

6 B.1. Line Graph (Time Plot) A line graph is graphic representation for a time series. Time series are data collected at different time period. & Eample: The following data are daily high temperatures from Monday through Friday: The line graph for the temperatures is 80 Temperature Temperature Monday Tuesday Wedn. Thursday Friday Date & Eample: The line graph of IBM stock price is IBM Stock Price Price Date Tetbook Eercises:.-.9, pages -3; , pages

7 Ecel: Create a Line Graph 1. Click on Insert.. Click on Chart. 3. In Chart-Wizard Step 1: Select Line and the top-left line chart; click Net. 4. In Chart-Wizard Step : Click Series tab, Values contains data, Category (X) ais labels contains the values of date or time. Click Net and complete the rest steps. B. Measures of Central Tendency (Section 3.1) To describe data sets numerically, we use mean, median, range, and standard deviation. B..1 Mean (Average) The mean of a collection of n data values is the sum of the data values divided by n. & Eample: Calculate the mean of the following daily high temperatures: The mean is = Notation: Sum and Mean Suppose there is a collection of n data values. These values are represented by 1,, K,,. The n sum of these values is denoted as n i i= 1 The mean is equal to. n i=1 n i. Sample Mean, X The mean of a sample of n data values, 1,, K n is denoted as X. And n i i= X = 1. n 7

8 O Eercise: Prices of product A Suppose the prices of product A in the past five months are Calculate the mean. Answer: Population Mean, μ The mean of a population is denoted as μ. If the data values of are represented by then the population variance is defined as N i i= μ = 1. N, 1,, K N, B.. Median The median of a collection of data values is the data value in the middle position for sorted data. & Eample: Calculate the median of the following daily high temperatures: The sorted data are The median is 74. Tetbook Eercises: , pages

9 B.3 Measures of Variability (Section 3.) B.3.1 Range The range of a collection of data values is the difference between the largest and the smallest values. & Eample: Calculate the range of the following daily high temperatures: The range is = 8. & Eample: Sale Prices for Residential Properties Calculate the range. The range is = 11. O Eercise: YTD Returns Calculate the range. The range is B.3. Variance and Standard Deviation The variance is used to measure the variation of the data values from its mean. The variance of a collection of data values is defined to be the average of the squares of the deviations of the data values about their mean. s Sample Variance, The variance of a sample of n data values 1,, K, n is defined as s = n ( i X ) i= 1 n 1. & Eample: Prices of product A Suppose the prices of product A in the past five months are Calculate the mean and the variance. 9

10 i i deviation i X (deviation) ( X ) i = = = = = 1 1 Sum The sample mean is X = = The sample variance is s = = Alternative Formula: A shortcut formula to compute s is ( ) n ( X ) s = n 1 i. & Eample: Prices of product A Suppose the prices of product A in the past five months are Use a shortcut formula to compute the sample variance. 10

11 i i i Sum The sample mean is X = = 4. 5 ( ) n ( X ) The sample variance is s = n = =.5. 4 O Eercise: Prices of product B Suppose the prices for product B in the past five months are Calculate the sample mean and the sample variance. i Sum 0 The sample mean is i i i The sample variance is 11

12 Standard Deviation The standard deviation of a collection of data values is equal to the square root of their variance. Sample Standard Deviation, s s = s. & Eample: Prices of Product A The sample standard deviation is s =.5 = O Eercise: Prices of Product B Calculate the sample standard deviation. The sample standard deviation is Population Variance σ and Population Standard Deviation σ The population variance is denoted as σ. For a population with the data values of and the mean μ, population variance is defined as σ = n i= 1 (i - μ ). N The population standard deviation is σ = σ.,,, 1 K Note: Sample mean X, variance s, and standard deviation s are sample statistics. Population mean μ, variance σ, and standard deviation σ are population parameters. Tetbook Eercises: , , pages N 1

13 B.4 Skewness and Kurtosis We use skewness and kurtosis to show the shape of distribution. B.4.1 Skewness The skewness measures the amount of asymmetry in a distribution or in a relative frequency histogram. If a distribution is symmetric, skewness equals zero; the larger the absolute size of the skewness statistic, the more asymmetric is the distribution. The measure of sample skewness is defined as ( X ) 1 3 i skewness = n. 3 s When skewness has a large positive value indicates a long right tail. When skewness has a large negative value indicates a long left tail. & Eample: Sale Prices The data set has a positive skewness. Hence, the distribution has a long right tail. Column1 Mean 81 Standard Error Median 76 Mode #N/A Standard Deviation Sample Variance Kurtosis Skewness Range 11 Minimum 36 Maimum 148 Sum 05 Count 5 B.4. Kurtosis The kurtosis is a measure of the thickness of the tails of its distribution (or relative frequency histogram) relative to those of a normal distribution. A normal distribution has a kurtosis of three. A kurtosis above three indicates Afat The measure of sample kurtosis is defined as ( X ) 1 4 i Kurtosis = n. 4 s 13

14 & Eercise: YTD Returns Column1 Mean 1.1 Standard Error Median 0.85 Mode 0.6 Standard Deviation Sample Variance Kurtosis Skewness Range 13.9 Minimum -4.3 Maimum 9.6 Sum 33.6 Count 30 Tetbook Eercises: 3.4, 3.6, , pages 50, 51. Ecel: Descriptive Statistics (See Appendi) 1. Click on Tools.. Click on Data Analysis. (If Data Analysis is not on the list, click and Check AAnalysis to install the add-in from Microsoft Office CD.) 3. Select Descriptive Statistics; click OK. 4. Complete dialog bo: Input range contains data; Output range contains the starting cell with descriptive statistics; select Summary statistics. Click OK. 14

15 C. Random Variables and Normal Distribution (Sections , 6.1, 6.3) C.1 Random Variables (Section 5.1) Part I (Chapters 1 11) Random Eperiment: A random eperiment is a process leading to two or more possible outcomes with uncertainty as to which outcome will occur. Random Variable: A random variable is a variable that takes on numerical values determined by the outcome of a random eperiment. Usually, there are two usages of random variables. Random Variables for a Population: We can use a random variable to represent different possible data values for a population. This random variable has a probability distribution. & Eample: The sale price can be represented by a variable X. Then different data values of sale price can also be represented by ( 1,, K, n ). The population mean is denoted as μ X and the population standard deviation isσ X. Random Variables for Statistical Analysis: Some random variables have interesting probability distributions. These probability distributions are useful in statistical inference. & Eample: The random variable Z has a standard normal distribution. There are two types of random variables. One is discrete random variable and the other is continuous variable. Discrete Random Variable: Continuous Random Variable: A discrete random variable takes some countable number of values. A continuous random variable is a random variable taking values on a line interval. & Eample: Age in years - Discrete random variable Income - Discrete Prices - Discrete Temperature - Continuous Height - Continuous Growth rates - Continuous 15

16 C. Discrete Random Variable (Sections 5., 5.3) The probability distribution of a random variable X is denoted as P(). The properties of P() are a. ( ) 0 b. ( ) P. P = 1. & Eample: New Products Suppose the number of new products introduced each year is a random variable X. The values and the probabilities of Χ are P ( ) Mean and Standard Deviation The mean of a discrete random variable X is ( ) μ = P. The mean of is also called the epected value of X, ( ) = ( ) E Χ P. The variance of a discrete random variable X is ( ) P( ) σ =. μ 16

17 & Eample: New Products Calculate the mean and standard deviation. P ( ) P( ) μ ( ) ( μ ) P( ) μ Sum The mean is μ = The variance is σ = The standard deviation is σ = 0.84 = O Eercise: Returned Checks Suppose the number of returned checks in a day for a department store is a random variable X. The values and the probabilities of X are P ( ) Calculate the mean, variance, and standard deviation. 17

18 P ( ) P( ) μ ( μ ) ( μ ) P( ) Sum The mean is The variance is The standard deviation is Alternative Formula for Calculating Variance: A shortcut formula to compute σ is ( P( ) ) μ σ =. & Eample: New Products The variance is P ( ) P( ) P( ) Sum ( P( ) ) μ = σ = =. 18

19 O Eercise: Returned Checks P ( ) P( ) P( ) Sum The variance is σ X = Tetbook Eercises: , pages 136, 137; , , pages C.3 Continuous Random Variable (Sections 6.1, 6.3, 8.3) The probability distribution of a random variable X can be denoted as f ( ) probability distribution of X has the following properties: a. f ( ) 0. b. Total area under f ( ) is one. c. The probability of falling within an interval ( a, b) is denoted as P ( a < < b). It is the area under the curve ( ) f between a and b. One of the most commonly used continuous random variable is normal random variable. C.3.1 Normal Distribution (Section 6.3). The Normal Random Variable and Normal Probability Distribution A normal random variable with a normal probability distribution has the following properties: a. The probability distribution has a bell-shaped. b. The distribution is symmetric about its mean μ. c. The spread of the distribution is determined by the standard deviation σ. d. Any normal random variable X with mean μ and standard deviation σ can be standardized as a standard normal random variable. X μ Z =. σ 19

20 Standard Normal Random Variable A standard normal random variable is a normal random variable with mean zero and standard deviation one. The probability table for standard normal random variable shows the probability of ( < Z a) P 0 <. Using Standard Normal Probability Distribution Table Case 1. Find P ( < Z < a) & Eample: 0. ( 0 < Z < 1.) = ( 0 < Z < 1.76) = P. P. O Eercise: P ( 0 < Z < 1. 64)= P ( 0 < Z < 1. 96)= Case. Find ( a < Z < 0) P. & Eample: P ( 1. < Z < 0) = P ( 1.76 < Z < 0) = P ( Z < 0 ) = P Z > 0 = 0.. ( ) 5 O Eercise: P ( 1.8 < Z < 0)= P (.33 < Z < 0)= Case 3. Find ( Z a) & Eample: P <. ( Z < 1.) = = ( Z < 1.76) = = P. P. 0

21 Note: We denote the cumulative probability as F ( a), such that F ( a) P( Z < a) O Eercise: P ( Z < 1. 64)= P ( Z < 1. 96)= Case 4. Find ( Z a) & Eample: P >. ( Z > 1.) = = ( Z > 1.76) = = P. P. O Eercise: P ( Z > 1. 64)= P ( Z. > 1. 96)= P ( Z > 1. 8)= P ( Z >. 33)= Case 5. The probability P ( < Z < a) & Eample: P( 0 < Z < a) = 30%. What is a? From the table, a = O Eercise: P 0 < Z < a = 40. What is a? ( ) % 0 is given. Find the value of a. Part I (Chapters 1 11) =. Case 6. The probability ( Z a) P > is given. Find the value of a. & Eample: P ( Z > a) = 5%, find a. The point a locates on the right-hand side of origin and P ( 0 < Z < a) = = With the given probability 0.45, we find a = from the table. 1

22 O Eercise: P ( Z > a) = 0. 10, find a. Answer: Tetbook Eercises:6.17, 6.18, page 07. Probabilities for Normal Random Variables Let X be a normal random variable with mean μ and variance σ. Then random variable X μ Z = is a standard normal random variable. Also, σ a μ b μ P ( a < X < b) = P < Z <. σ σ & Eample: A company produces light bulbs whose life follows a normal distribution with mean 1,00 hours and standard deviation 50 hours. If we choose a light bulb at random, what is the probability that its lifetime will be between 900 and 1,300 hours? Answers: P ( 900 < X < 1300) X = P < < = P 1. < Z < 0.4 = = 0.. ( ) 5403 O Eercise: Anticipated consumer demand for a product net month can be represented by a normal random variable with mean 1,00 units and standard deviation 100 units. a. What is the probability that sales will be between 1,000 and 1,300 units? b. What is the probability that sales will eceed 1,100 units? Answers: Tetbook Eercises: 6.19 abc, 6.0 abc, 6.1 abc, 6. abd, 6.3 ab, 6.4 abc, 6.5, 6.6, 6.7 a, 6.31 ab, 6.35 ab, 6.36a, 6.37 ab, pages

23 C.3. Student=s t Distribution (Section 8.3) Student's t Distribution (t -distribution) Let t be a random variable with t -distribution. Properties of t -distribution: 1. Bell-shaped.. Symmetrical about t = The probability distribution has tails that are more spread out than the standard normal distribution. 4. The shape of probability distribution depends on a constant, the degrees of freedom (v). 5. When v is large, t distribution is close to the standard normal distribution. t Statistical Table The table shows the value of t α, such that ( t > t α ) = α P. For α = 0. 01, = α, and α = 0. 05, the values of t α for different v are v t. 05 t. 05 t

24 & Eample: Find the value a such that, a. P ( t > a) = when v = 5. b. P ( t < a) = when v = 10. c. P ( t > a) = when v = 0. Answer: a: a =. 015 ; b: a =. 8; c: a =.58. O Eercise: Find the value a such that, a. P ( t > a) = when v = 5. b. P ( t < a) = when v = 10. c. P ( t > a) = when v = 15. Answer: 4

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