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NMDS 2.0 Program Description Dealing with Missing Values (MV) Basic Knowledge about the Interface This is a usual Power Point Presentation. Use Mouse-Clicks or the Hyperlinks to proceed. How to start a NMDS Dealing with the Temperature Option

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The Menu of NMDS The menu of NMDS is very simple Each topic directly leads to a window of the application

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The Menu of NMDS The menu of Access calls the Access data-base that contains the rank-matrixes. Call this option to import your own matrix. You, for instance, can simply import any correlation matrix generated by excel using the access import filter and visualize the relations using NMDS The list of all matrixes that are stored in the Access database are listed in this combo box

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The NMDS Rank-Matrix This is the examle rank-matrix of the example “Staedte” (towns) This is the classical example in psychological text-books.

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The NMDS Rank-Matrix This is the example rank-matrix based on reaction times (1/100-seconds) typing several letters with a QWERTY keyboard

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The NMDS Rank-Matrix This is the example rank-matrix based on an imported correlation matrix produced in EXCEL and imported in ACCESS

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If you start NMDS, you see the following Windows. This is the Information Line showing you the actual Progress of the NMDS This is the Option Box where you select the Rank Matrix you want to elaborate Here you have to adjust whether high values in the rank-matrix mean similarity or no-similarity Here you choose the dimensionality of the NMDS graph (since a screen only has a 2D presentation, usually keep the default) Here you select how to deal with missing values The Interface - NMDS Control 1/5 This button loads the specified rank-matrix

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This button starts the NMDS calculation The Interface - NMDS Control 2/5 Here you select the Random Algorithm you want to use for calculation (usually you*ll keep 0 as default) This option box determines the temperature for the NMDS calculation This option box determines what is affected by the temperature

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This button shows you the NMDS graph This is the information that is generated automatically with each start of the program This option decides whether the information in the text-field is presented on the NMDS graph The Interface - NMDS Control 2/5 In this field you can specufy how long the labels are on the NMDS graph This option box determines the size of NMDS graph Mirroring the NMDS graph horizontally Mirroring the NMDS graph vertically Rotating the NMDS graph in steps of 45 degrees

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An information field of the actual calculated alienus An information field of the actual iterations calculated The Interface - NMDS Control 4/5 This button shows you the Alienus graph Switching into the single step mode (you then have to press a key for each iteration step)

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The Interface - NMDS Control 5/5 This button stops and continues the NMDS calculation This button terminates the NMDS program This button exports the NMDS calculation into *.txt files This button prints the NMDS graph on the standard printer

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Click into this window to refresh the NMDS drawing Use right button to move an item The Interface - NMDS Graph Moving an item manually is useful to test certain hypotheses about relationships of variables

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The Interface - Alienus Monitor The Alienus Monitor shows the development of the alienus over time. It is useful to set the appropriate temperature for a give rank matrix

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How to Start a NMDS 1. Press here 2. Press here 3. Press here 4. Press here 5. Enter 10 here 6. Press here & wait To see how NMDS is working just try the default “Städte” (towns)

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How to deal with Missing Values (MV) NMDS has various options to deal with Missing Values (MV) by choosing several options in this combo-box

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How to deal with Missing Values (MV) Missing-Values can be treated with the following options MV set to -1 All MV are set to -1 MV set to 0 All MV are set to 0 inverse-single Optimal Option if the Rank-Matrix contains values from 0 to 1 positive-double Optimal Option if the Rank-Matrix contains values from 1 onwards negative-double Option if the Rank-Matrix contains values from 0 to 1 and the MV are to be distinguished very clearly from known values inverse-double Option if the Rank-Matrix contains values from 0 to 1 and the MV are to be distinguished clearly from known values all-inverse Fits to all problems that cannot be treated with means above

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The Temperature Option The temperature Option is a highly efficient option to avoid local minima in a NMDS calculation. A temperature of 0 would, for instance lead to about 1%-4% wrong representations in a simple Example with about 10 varibales and a defined optimal solution, as “Städte” (towns) in this software package. Using a temperature of 1.0 for this example reduces this error to zero, i.e. in all times the optimal minimum is found. Set the temperature in a way that the calculated points are “shaken” and cooled down in order to find the best fit of the NMDS graph to your rank matrix. Consider the following experience-based suggestions: For 10 Variables:Temperature set to 0.5 or higher For 30 Variables:Temperature set to 1.0 or higher For 90 Variables:Temperature set to 3.0 or higher

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The Temperature Option. Input the value for the temperature as you like here. The most efficient value for about 10 variables in terms of time and result-quality for the temperature is preset. There are two algorithms implemented how the temperature boils the points in the NMDS graph. “Dots+Alineation” or “Alineation” “Dots+Alineation” is more efficient in finding local minima “Alineation” is more efficient in terms of time until the solution is found

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The Temperature Option Without the temperature, a Rank-Matrix may fall into a local minimum. This means, the NMDS will not find the optimal interrelation of the variables The temperature avoids that a NMDS graph falls into a local minimum and fixes 90% to 100% of all possible local mimima. In general the Alienus-Monitor is showing a graph like the green one if the temperature has successfully overcome a local minima

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The Temperature Option Don’t worry, if the NMDS graph looks like this during the NMDS calculation. The temperature cools down with each iteration so that an optimum is found after a certain amount of interations. The absolute number of iterations required depends on the quality of the data as well as the temperature set

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Showdown Return to NMDS 2.0 Mail Comment to Development Visit the Web-site for further Information © Oliver Straeter

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