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The common trend of the world nowadays is regional economic integration, which has taken place for a long time in European countries, under the name as European Union (EU) with 15 member countries, then in North America with North American Free Trade Area (NAFTA) including 3 countries, and most recently in Southeast Asia with ASEAN Free Trade Area (AFTA) including 10 countries. The abovesaid establishments of free trade areas were aimed at eliminating tariff and nontariff barriers, enhancing exchange relations of goods and services among member countries and nonmember countries. Products and services must be participated into a free competition, a positive factor of a market economy, without any protection from the government. In such economic context and environment, if an enterprise wants to enter foreign markets, its products and services must have reasonable prices, attractive designs and many features that meet demands and tastes of consumers. That enterprise must find to understand the import trend of a country, which rises or falls year by year, in order to forecast import evolutions in the longterm and in the shortterm, that is, it must conduct careful studies on import markets before working out their production plans.
11/29/2017 CHAPTER SPREADSHEET MODELS Introduction u Spreadsheet models are mathematical and logic-based models u Referred to as what-if models u Provide easy-to-use, logical functions sophisticated mathematical and u Allow for easy instantaneous recalculation for a change in model inputs u Are less expensive u Often come preloaded on computers u Are fairly easy to use u The most used business analytics tool 11/29/2017 Building Good Spreadsheet Models INFLUENCE DIAGRAMS BUILDING A MATHEMATICAL MODEL SPREADSHEET DESIGN AND IMPLEMENTING THE MODEL IN A SPREADSHEET Building Good Spreadsheet Models u u Total cost of manufacturing a product is the sum of two costs: u Fixed cost: Portion of the total cost that does not depend on the production quantity and remains the same no matter how much is produced u Variable cost: Portion of the total cost that is dependent on and varies with the production quantity Make-versus-buy decision: comparing the costs of manufacturing in-house to the costs of outsourcing production to another firm 11/29/2017 Building Good Spreadsheet Models • Example: • Nowlin Plastics produces a line of cell phone covers Nowlin’s best-selling cover is its Viper model, a slim but very durable black and gray plastic cover The annual fixed cost for the Viper cover is $234,000 • This fixed cost includes management time, advertising, and other costs that are incurred regardless of the number of units eventually produced • In addition, the total variable cost, including labor and material costs, is $2 for each unit produced Building Good Spreadsheet Models Influence Diagrams u An influence diagram is a visual representation that shows which entities influence others in a model u Parts of the model are represented by circular or oval symbols called nodes, and arrows connecting the nodes show influence 11/29/2017 Figure 6.1: An Influence Diagram for Nowlin’s Manufacturing Cost Figure 6.2: An Influence Diagram for Comparing Manufacturing Versus Outsourcing Cost for Nowlin Plastics 11/29/2017 Building Good Spreadsheet Models Building a Mathematical Model u Consider the cost of manufacturing the required units of the Viper u As the influence diagram shows, this cost is a function of the fixed cost, the variable cost per unit, and the quantity required u Define notation for every node in the influence diagram: u q = quantity (number of units) required u FC = the fixed cost of manufacturing u VC = the per-unit variable cost of manufacturing u TMC(q) = total cost to manufacture q units Building Good Spreadsheet Models u u u 10 The cost-volume model for producing q units is TMC(q) = FC + (VC × q) For the Viper, FC = $234,000 and VC = $2, so TMC(q) = $234,000 + $2q Mathematical model for purchasing q units is TPC(q) = Pq P = the per unit purchase cost TPC(q) = the total cost to outsource or purchase q units u For the Viper, since P = $3.50, TPC(q) = 3.5q 11/29/2017 Building Good Spreadsheet Models 11 u Mathematical model for the savings associated with outsourcing S(q) = TMC(q) – TPC(q) S(q) = the savings due to outsourcing u Nowlin has to decide, “For what quantities is it more cost-effective to outsource rather than produce the Viper?” u Mathematically, this question is, “For what values of q is S(q) > 0?” Building Good Spreadsheet Models 12 Spreadsheet Design and Implementing the Model in a Spreadsheet u For the Nowlin Plastics problem, we have defined the following components: q, FC, VC, TMC(q), P, TPC(q), S(q) u TMC, TPC, and S are the functions of other components, whereas q, FC, VC, and P are not u TMC, TPC, and S will be formulas involving other cells in the spreadsheet model, whereas q, FC, VC, and P will just be entries in the spreadsheet 11/29/2017 Building Good Spreadsheet Models 13 u The number of Vipers to make or buy for next year is really a decision Nowlin gets to make, hence we refer to quantity q as a decision variable u FC, VC, and P are measurable factors that define characteristics of the process we are modelling, hence we refer to FC, VC, and P as parameters Figure 6.3: Nowlin Plastics Make14 Versus-Buy Spreadsheet Model 11/29/2017 Building Good Spreadsheet Models u 15 The general principles of spreadsheet model design and construction are: u Separate the parameters from the model: This enables the user to update the model parameters without the risk of mistakenly creating an error in a formula u Document the model and use proper formatting and color as needed: A good spreadsheet model is well documented Clear labels and proper formatting and alignment facilitate navigation and understanding u Use simple formulas: Clear, simple formulas can reduce errors and make maintaining the spreadsheet easier Long and complex calculations should be divided into several cells What-If Analysis DATA TABLES GOAL SEEK 11/29/2017 What-If Analysis 17 Data Tables u Data Table: Excel tool which quantifies the impact of changing the value of a specific input on an output of interest u One-way data table: summarizes a single input’s impact on the output u Two-way data table: summarizes two inputs’ impact on the output Figure 6.4: The Input for Constructing 18 a One-Way Data Table for Nowlin Plastics 11/29/2017 Figure 6.5 Results of One-Way 19 Data Table for Nowlin Plastics Figure 6.6: The Input for Constructing 20 a Two-Way Data Table for Nowlin Plastics 10 11/29/2017 21 Figure 6.7: Results of Two-Way Data Table for Nowlin Plastics What-If Analysis 22 Goal Seek u Goal Seek: Excel tool that allows the user to determine the value of an input cell that will cause the value of a related output cell to equal some specified value (the goal) u In the case of Nowlin Plastics, suppose we want to know the value of the quantity of Vipers where it becomes more cost effective to manufacture rather than outsource 11 11/29/2017 Figure 6.8: Goal Seek Dialog Box 23 for Nowlin Plastics Figure 6.9: Results from Goal Seek for 24 Nowlin Plastics 12 11/29/2017 Some Useful Excel Functions for Modeling SUM AND SUMPRODUCT IF AND COUNTIF VLOOKUP Some Useful Excel Functions for Modeling26 SUM and SUMPRODUCT u SUM: Function that adds up all of the numbers in a range of cells u SUMPRODUCT: Function that returns the sum of the products of elements in a set of arrays 13 11/29/2017 Figure 6.10: What-If Model for Foster Generators 27 28 Some Useful Excel Functions for Modeling IF and COUNTIF u =IF(condition, result if condition is true, result if condition is false) u =COUNTIF(range, condition) u Counts the number of components having a positive order quantity Illustration: u Gambrell Manufacturing produces car stereos u Gambrell likes to keep its components inventory to a minimum u Hence, it uses an inventory policy known as an order-up-to policy u Order-up-to policy: Whenever the inventory on hand drops below a certain level, enough units are ordered to return the inventory to that predetermined level 14 11/29/2017 29 Figure 6.11: Gambrell Manufacturing Component Ordering Model 30 Some Useful Excel Functions for Modeling VLOOKUP u This function allows the user to pull a subset of data from a larger table of data based on some criterion u General form =VLOOKUP(value, table, index, range) where, value = the value to search for in the first column of the table table = the cell range containing the table index = the column in the table containing the value to be returned range = TRUE if looking for the first approximate match of value and FALSE if looking for an exact match of value 15 11/29/2017 31 Figure 6.12: Granite Insurance Bonus Model Auditing Spreadsheet Models TRACE PRECEDENTS AND DEPENDENTS SHOW FORMULAS EVALUATE FORMULAS ERROR CHECKING WATCH WINDOW 16 11/29/2017 Auditing Spreadsheet Models 33 u Excel contains a variety of tools to assist you in the development and debugging of spreadsheet models u These tools are found in the Formula Auditing group of the Formulas tab Auditing Spreadsheet Models 34 Trace Precedents and Dependents u Trace Precedents button: After selecting cells, this button creates arrows pointing to the selected cell from cells that are part of the formula in that cell u Trace Dependents button: Shows arrows pointing from the selected cell to cells that depend on the selected cell u Both of the tools are excellent for quickly ascertaining how parts of a model are linked 17 11/29/2017 Figure 6.13: The Formula Auditing Group Figure 6.14: Trace Precedents for Foster 36 Generator 18 11/29/2017 Figure 6.15: Trace Dependents for37 the Foster Generators Model Auditing Spreadsheet Models 38 Show Formulas u To see the formulas in a worksheet, simply click on any cell in the worksheet and then click on Show Formulas—you will see the formulas residing in that worksheet u To revert to hiding the formulas, click again on the Show Formulas button 19 11/29/2017 Auditing Spreadsheet Models 39 Evaluate Formulas u The Evaluate Formulas button allows you to investigate the calculations of a cell in great detail u Provides an excellent means of identifying the exact location of an error in a formula Figure 6.16: The Evaluate Formula Dialog Box for Gambrell Manufacturing 20 11/29/2017 Figure 6.17: The Evaluate Formula Dialog 41 Box for Gambrell Manufacturing Cell B17 after Four Clicks of the Evaluate Button Auditing Spreadsheet Models 42 Error Checking u The Error Checking button provides an automatic means of checking for mathematical errors within formulas of a worksheet u Clicking on the Error Checking button causes Excel to check every formula in the sheet for calculation errors u If an error is found, the Error Checking dialog box appears 21 11/29/2017 Figure 6.18: The Error Checking Dialog 43 Box for a Division by Zero Error Auditing Spreadsheet Models 44 Watch Window u The Watch Window, located in the Formula Auditing group, allows the user to observe the values of cells included in the Watch Window box list u Useful for large models when not all of the model is observable on the screen or when multiple worksheets are used 22 11/29/2017 Figure 6.19: The Watch Window for Cell 45 B17 of the Gambrell Manufacturing Model 23 ... the output Figure 6. 4: The Input for Constructing 18 a One-Way Data Table for Nowlin Plastics 11/29/2017 Figure 6. 5 Results of One-Way 19 Data Table for Nowlin Plastics Figure 6. 6: The Input for... of a model are linked 17 11/29/2017 Figure 6. 13: The Formula Auditing Group Figure 6. 14: Trace Precedents for Foster 36 Generator 18 11/29/2017 Figure 6. 15: Trace Dependents for37 the Foster Generators... identifying the exact location of an error in a formula Figure 6. 16: The Evaluate Formula Dialog Box for Gambrell Manufacturing 20 11/29/2017 Figure 6. 17: The Evaluate Formula Dialog 41 Box for Gambrell