1.2 Continuous Data

Stemplot (or Stem-and-leaf plot) is another way of organizing (and displaying) data.

Stem 0 1 2 3 4 5

Leaf 9 7 1 8 3 6 7 6 4 9 3 5 5 6 8 2 1 7 9 3 4 2 1

The stem and leaf plot helps you organize the individual entries by breaking up the number into different columns. At the row 1 | 7 1 means there are entries of 17 and 11 in the data set.

The stem-and-leaf plot is called ‘ordered’ if the entries are, you guessed it, ordered.

Stem 0 1 2 3 4 5

Leaf 9 1 7 3 4 6 6 7 8 1 2 3 5 5 6 8 9 2 3 4 7 9 1

You can group two sets similar data in back to back stemplots.

Ex 1 A swimming squad recorded the times of the latest 100m freestyle practice.

Girls: 35.3, 34.7, 38.6, 36.8, 34.6, 36.8, 36.3, 37.6, 37.7, 36.3, 34.3, 35.7, 35.4, 37.6, 35.8, 37.6, 32.4

Boys: 36.8 32.1 33.2 36.7 33 34.1 34.4 35 35.7 35.9 34.4 35.9 36.8 33.7 34.3 35.4 33.2 37 34.8 35.2

Girls 4 7 6 3 8 7 4 3 0 8 8 3 3 7 6 6 6 6 0

32 33 34 36 36 37 38 39 40 41

Boys 1 0 2 2 7 1 3 4 4 8 0 2 4 7 9 9 7 8 8 0

Remember, context is everything. In this case the leaves represent the first decimal place. Be sure to define somewhere what your units are.

Grouping Discrete Data

In larger data sets, it might not be feasible to use represent all the data individually. For these cases, we group the data using appropriate intervals. Depending on the size of your data set, it is advisable to use between 5 and 20 data sets. Consider the range of your data and make a decision as to how many intervals would be appropriate. All intervals must be the same length.

Continuous Data

To organize continuous data in a frequency table, you must use intervals. Due to the nature of the numbers, you define the bottom end of the interval only-as opposed to discrete.

Interval 50 – 60 – 70 – 80 – 90 –

Frequency 2 7 9 5 3

To display the data we use a histogram. A histogram is like a bar graph but has the bars touching to indicate the continuous nature of the data.

Ex 2 Create a histogram for the data given in the frequency table.

p. 120#1-5

p. 123#1-3