It comes from the fact that there is 1 leaf in the first (6) stem and 0 leaves in the second (the first 7) stem, and so 1 + 0 = 1. The second number in the depths column is also a 1. It comes from the fact that there is just one number in the first (6) stem. For example, the first number in the depths column is a 1.
The depths are the frequencies accumulated from the top of the plot and the bottom of the plot until they converge in the middle. That column contains what are called depths.
Now, back to that first column of numbers appearing in Minitab's plot. Minitab orders the data before producing the plot, and thereby creating what is called an ordered stem-and-leaf plot.
Sometimes the one row per stem option produces the better plot, and sometimes the two rows per stem plot option produces the better plot.ĭo you notice any other differences between Minitab's plot and our plot? Note that the leaves in Minitab's plot are ordered. The decision to use one or two rows for the stems depends on the data. For example, note that the first 9 row contains the 0 to 4 leaves, while the second 9 row contains the 5 to 9 leaves. When you opt to use two rows for each stem, the first row is reserved for the leaves 0, 1, 2, 3, and 4, while the second row is reserved for the leaves 5, 6, 7, 8, and 9. Minitab takes an alternative here that we could have taken as well. Note, though, that Minitab uses two rows for each of the stems 7, 8, 9, 10, 11, 12, and 13. Then, ignoring the first column of numbers for now, the second column contains the stems from 6 to 14. how does the plot differ from ours? First, Minitab tells us that there are n = 64 numbers and that the leaf unit is 1.0. Here's what Minitab's stem-and-leaf plot of the 64 IQs looks like: Stem-and-Leaf of IQ Instead, you'd probably want to let some statistical software, such as Minitab or SAS, do the work for you. First and foremost, no one in their right mind is going to want to create too many of these stem-and-leaf plots by hand. That's all well and good, but we could do better. the smallest IQ in the data set is 68, while the largest is 141.most of the IQs are in the 90s and 100s.Now, rather than looking at a list of 64 unordered IQs, we have a nice picture of the data that quite readily tells us that: Here's what the our stem-and-leaf plot would look like after adding the first five numbers 111, 85, 83, 98, and 107:Īnd here's what the completed stem-and-leaf plot would look like after adding all 64 leaves to the nine stems: Once the column of stems are written down, we work our way through each number in the data set, and write its leaf in the row headed by its stem. To create the plot then, we first create a column of numbers containing the ordered stems. We could divide 83 into a stem of 8 and a leaf of 3. We could divide 85 into a stem of 8 and a leaf of 5. We could divide our first data point, 111, for example, into a stem of 11 and a leaf of 1. The basic idea behind a stem-and-leaf plot is to divide each data point into a stem and a leaf. A stem-and-leaf plot, on the other hand, summarizes the data and preserves the data at the same time. One primary disadvantage of using a histogram to summarize data is that the original data aren't preserved in the graph.
We could, of course, summarize the data using a histogram. Once the data are obtained, it might be nice to summarize the data. After each person completed the test, they were assigned an intelligence quotient (IQ) based on their performance on the test. A random sample of 64 people were selected to take the Stanford-Binet Intelligence Test.
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