Basic Tools Of Quality

Basic Tools Of Quality

1. Control Charts

   • Control chart for variables
     • Graph X
       • Used to track the level of the process and detect the presence of special causes that affect the average
     • Graph R
       • Used to track process variation and detect unexpected variation.
     • Graph X-R
       • We use both types of plots when measuring the relationship of quality specifications with central tendency and dispersion.
     • Zone Graph
       • Plots cumulative scores based on "zones" at 1, 2, and 3 standard deviations from the center line. Use it to detect an unexpected variation.
     • Graph S
       • It is used to monitor the variation of the process when you have continuous data andd subgroup sizes of 9 or more.
   • Control Chart by atributtes
     • Graph U
       • percentage of defects in a unit.
     • Graph C
       • It is the number of defects per unit of production
     • Graph NP
       • number of defective units in a sample.
     • Graph P
       • percentage of defects per sample.

2. Frequency distribution

   • The purpose of frequency groupings is to facilitate obtaining the information contained in the data.
     • Absolute frequency (fi)
       • It is the number of observations that belong to each group.
     • Relative frequency (hi)
       • It is calculated by dividing the absolute frequency by the number of data.
     • Accumulated absolute frequency (Fi)
       • t results from adding the absolute frequencies of a class or group of the sample (or population) with the previous one or the previous ones.
     • Cumulative relative frequency (Hi)
       • It is the result of adding the relative frequencies

3. Measures

   • Measures of central tendency
     • Aim to summarize a set of values in a single value
       • Average or Mean
         • It is calculated by adding a group of numbers and then dividing by the count of those numbers
       • Median
         • It is a set is a value that is in the middle of the other values, that is, when ordering the numbers from smallest to largest, it is exactly in the middle.
       • Mode
         • It is the value that appears most frequently in a data set.
   • Measures of dispersion
     • Measure the degree of dispersion of the values of the variable.
       • Variation Range
         • It is defined as the difference between the highest value of the variable and the lowest value of the variable.
       • Variance
         • The variability of a data set with respect to its mean. Formally, it is calculated as the sum of the squared residuals divided by the total number of observations.
       • Typical deviation
         • Provides information on the dispersion with respect to the mean. Its calculation is exactly the same as the variance, but taking the square root of its result.
       • Coefficient of variation
         • Its calculation is obtained by dividing the standard deviation by the absolute value of the set mean and is usually expressed as a percentage.

4. Statistics

   • It is a numerical quantity calculated on the sample that summarizes its information on some aspect. It is used to approximate a parameter.

5. Parameters

   • It is a numerical quantity calculated on a population and summarizes the values that this takes on some attribute.
   • Try to summarize all the information in the population in a few numbers (parameters) example: the average height of the subjects.