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7 QC Tools: Scatter Chart (Video Tutorial)

What is a Scatter Chart?

  • A graphical tool
  • Correlates two variables, one is independent on X-Axis, and other is dependent on Y-Axis
  • Dot plot corresponding to independent vs dependent variables

Why does a Scatter Chart use as a qc tool?

  • Helps in understanding the degree of relationship between two variables
  • Helps in forecasting the future trend on the basis of current relationship between variables
  • Helps in understanding the behaviour of the dependent variable with change in independent variable
  • Confirms the independent variable actually causing the dependent variable

How does a Scatter Chart identify the relationship between two variables?

  • When the dot plot is on a straight line and moving from left to right in upward direction then it is perfect positive correlation
  • When the dot plot is on a straight line and moving from left to right in downward direction then it is perfect negative correlation
  • When the dot plot is scattered around a straight line and moving from left to right in upward direction then it is a high degree of positive correlation
  • When the dot plot is scattered around a straight line and moving from left to right in downward direction then it is a high degree of negative correlation
  • When the dot plot is scattered all over the graph then there is no correlation between variables and it is known as zero correlation

How does a Scatter Chart analyse the relationship between two variables?

  • Table 1 shows the data of speed and mileage for a vehicle
  • Now to analyse the relationship between speed and mileage you need to draw the scatter chart
  • To draw the scatter chart, take speed on X-Axis because speed is independent variable, and mileage on Y-Axis because mileage is dependent variable and it depends on the speed of the vehicle.
  • Now create the dot plot for mileage against each value of speed, and analyse the dot plot,
  • You can see here the dot plot is scattered around the line and moving from left to right in downward direction, hence speed and mileage have high degree of negative correlation,
  • This implies that mileage is decreasing most of the time while increasing the speed of the vehicle
  • Therefore, one should maintain the speed at an optimum level to get good mileage.
  • This way, scatter chart analyses, how dependent variable affected by independent variable?

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Last updated on: 04 July, 2017

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