Collecting and Processing Information

In this note, you will find information explaining why we need data, but also how to collect and process it.

Information: click the arrow to view the information

• Why do we need data?
    * Data is used throughout the Engineering Design Process to optimize designs and improve efficiency during production
    * Statistics refer to the collection and organization of data(science) as well as the analysis and presentation of those data(mathematics)
    * Statistics are often evaluated using the assistance of computers and software such as Microsoft Excel
    * Such tools allow user to easily access, collect, organize, maintain, manipulate, and interpret data – which helps to improve efficiency

Basic Statistics Vocabulary:

• Mean - the average of a given data set
• Median - the middle number in a given ordered set
• Mode - the most frequently occurring number in a given data set
• Standard Deviation - how much variation exists from the average(mean) in a given data set
• Range - the distribution of the data set or the difference between the largest and smallest values
• Tolerance - the amount of characteristic(product/part/dimension/etc) can vary without compromising(affecting) the overall function or design of the product
• Normal size - the size used in the general description of a part/product
• Basic size - the converted normal size(fraction to decimal) that can produce some deviation
• Upper Specification Limit - the highest acceptable deviation or value for a characteristic
• Lower Specification Limit - the lowest acceptable deviation or value for a characteristic
• Mean - the average of a given data set:
    * x = represents the data set
    * ∑ = the sum of a mathematical operation
    * n = the total number of variables in the data set
    * Equation for mean =     ∑x/n
      * Add the numbers in the data set first, then divide the product by the number of variables
• Median - the middle number in a given ordered data set
    * If the given data set has an even number of data, the median is the average of the two center data
      * Add the two numbers together then divide the product by 2
• Mode - the most frequently occurring number in a given data set
• Standard Deviation - Standard Deviation (SD) is a UNIT. It is used to measure the variability of individual data to the mean.
    * The smallest value that the standard deviation can be is 0. Standard deviation can not be negative.
      * Standard Deviation Steps Explained:
        * The mean must first be found through adding all numbers in a data set, and dividing by the pieces of data within the data set.
        * Subtract the mean from each value
        * Square the differences
        * Find the average of the squared numbers to find the variance
        * Square the variance to find the standard deviation
      * Calculating Standard Deviation
        * Equation for Standard Deviation  =  ∑(xi – μ)²

    √     n - 1
    * xi = represents the individual data
    * μ = represents the mean of the data set
    * ∑ = the sum of a mathematical operation
    * n = the total number of variables in the data set
    * The range is the distribution of the data set or the difference between the largest and smallest values in a data set

• Engineering tolerance is the amount a characteristic can vary without compromising the overall function or design of the product.
• Tolerances generally apply to the following:
    * Physical dimensions (part and/or fastener)
    * Physical properties (materials, services, systems)
    * Calculated values (temperature, packaging)
• American National Standards Institute (ANSI) standards.
    * Examples:
      * Bilateral Tolerance (1.125  0.025)
      * Unilateral Tolerance (2.575)