Exploring data: Graphs and numerical summaries
Exploring data: Graphs and numerical summaries

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Exploring data: Graphs and numerical summaries

5.4.2 Waiting times between geyser eruptions

Figure 20 shows a histogram of waiting times, varying from about 40 minutes to about 110 minutes.

Figure 4.3
Figure 4.3 Waiting times (minutes), source: Azzalini, A. and Bowman, A.W. (1990) A look at some data on the Old Faithful geyser. Applied Statistics, 39, 357–366.

In fact, these are waiting times between the starts of successive eruptions of the Old Faithful geyser in the Yellowstone National Park, Wyoming, USA, during August, 1985. Observe the two modes. These data are said to be bimodal.

Sometimes data sets may exhibit three modes (trimodal) or many modes (multimodal). You should be wary of too precise a description. Both the data sets in Figures 19 and 20 were based on large samples, and their message is unambiguous. As you will see later in the course, smaller data sets can give rise to very jagged histograms indeed, and any message about one or more preferred observations is consequently very unclear.

M248_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371