Create an R chart with summary data

Usually, you create an R chart from a column of individual measurements. However, you can also create an R chart from a column of subgroup ranges.

To create an R chart, Minitab needs to know the range and the sample size for each subgroup. For example, suppose that each row contains individual measurements for a subgroup. If a row contains the measurements 2, 6, and 7, Minitab calculates the range for the subgroup as 5 (7 minus 2) and the subgroup size as 3.

Now suppose that you only have a column of subgroup ranges, but you know that the subgroup size is 3. You can create 2 columns of zeros so that Minitab will calculate the correct ranges and sample sizes. For example, a row that contains the values 5, 0, and 0 results in the same range and subgroup size as a row that contains the individual measurements of 2, 6, and 7.

Example of creating an R chart using subgroup range data

For example, suppose that column C1 contains the ranges for 20 subgroups, and the subgroup size is 3.

  1. Enter 20 zeros in C2 and 20 zeros in C3. To enter all the zeros for a column in a single step, use Calc > Make Patterned Data > Simple Set of Numbers.
  2. Choose Stat > Control Charts > Variables Charts for Subgroups > R.
  3. Choose Observations for a subgroup are in one row of columns from the drop-down list, then enter C1 C2 C3.
  4. Click OK.