The seven basic tools of quality

The seven basic tools of quality

1. Cause and Effect Diagrams

   • Also Known as Ishikawa and Fishbone Diagrams
   • Identifies the symptoms of a problem or effect to find the root cause
     • The method forces the user to consider all the causes of a problem
       • Causes are identified by working backwards along the spines or vertebrae
   • Combines brainstorming techniques with graphical analysis

2. Control Chart

   • Used to determine if a manufacturing or business process is in a state of control.
     • If the process is under control
       • Data can be used to predict future perfomances of the process
     • If chart analysis indicates the process isn't under control
       • Data helps to determine the variation sources
   • Also known as Shewhart charts
   • Never adjust parameters if process is in control

3. The check sheet

   • Document that contains real time data from the location where is generated
     • Data is recorded by making marks on diferent regions
   • Designed to register info in a quickly, easy and efficient way
     • Quantitative or qualitative info
   • Check sheets types: Classification, location, frequency, measurements and check list

4. Histogram

   • Graphical representation of the distribution of data
     • Also can be normalized displaying relative frequencies
   • Tabulates frequencies as an adyacent rectangles
     • Rectangle area=frequency
     • Rectangle hight= interval density frecuency

5. Pareto chart

   • Combination of bars and line graphic
     • Bars=individual values
     • Lines=acumulative total
     • Purpose: to highlight a set of factors. In quality control represents the common sources of defects, the highest type of defect, costumer complaints and so on

6. Scatter plot

   • Mathematical diagram that uses Cartesian coordinates to display values for two variables
   • Suggests various kinds of correlations between variables with a certain confidence interval, for example: weight and hight
   • Powerful aspect: show no linear realtionships between variables.

7. Stratified sampling

   • Is a method of sampling from a population
     • Uses Stratification: process of dividing members of the population into homogeneous subgroups before sampling
       • Exmple: Political survey. If the respondents needs to reflect th diversity of the population such as race or religion
   • If population density varies greatly within a region, stratified sampling will ensure that estimates can be made with equal accuracy in different parts of the region
     • Disadvantage: Isn't useful in dissimilar subgroups