Bar charts can also be used to represent frequencies ofdifferent categories. A bar chart of the iMac purchases is
shown in
. Frequencies are shown on the Y
axis and the type of computer previously owned is shown on theX axis. Typically the Y-axis shows the number of observations
rather than the percentage of observations in each category asis typical in pie charts.
Bar chart of iMac purchases as a function of
previous computer ownership.
Often we need to compare the results of different surveys,or of different conditions within the same overall
survey. In this case, we are comparing the
distributions of responses between the surveys
or conditions. Bar charts are often excellent forillustrating differences between two distributions.
shows the number of people playing card
games at the Yahoo website on a Sunday and on a Wednesday on
a day in the Spring of 2001. We see that there were moreplayers overall on Wednesday compared to Sunday. The number
of people playing Pinochle was nonetheless the same on thesetwo days. In contrast, there were about twice as many people
playing hearts on Wednesday as on Sunday. Facts like theseemerge clearly from a well-designed bar chart.
A bar chart of the number of people playing different
card games on Sunday and Wednesday. The bars in
are oriented horizontally
rather than vertically. The horizontal format is useful whenyou have many categories because there is more room for the
category labels. Such
horizontal bar charts may
be contrasted with
vertical bar charts like the
one in
.
We'll have more to say about bar charts when we consider
numerical quantities later in this chapter. (See
Bar Charts .)
Some graphical mistakes to avoid
Don't get fancy! People sometimes add features to graphs that
don't help to convey their information. For example,3-dimensional bar charts like the one shown in
are usually not as effective as their
two-dimensional counterparts.
A three-dimensional version of
. Here is another way that fanciness can lead to
trouble. Instead of plain bars, it is tempting to substitutemeaningful images. For example,
presents
the iMac data using pictures of computers. The heights of thepictures accurately represent the number of buyers, yet
is misleading because the viewer's attention
will be captured by areas. This can exaggerate the sizedifferences between the groups. In terms of percentages, the
ratio of previous Macintosh owners to previous Windows ownersis about 6 to 1. But the ratio of the two areas in
is about 35 to 1. A biased person wishing to
hide the fact that many Windows owners purchased iMacs wouldbe tempted to use
instead of
!
Edward Tufte coined
the term
lie factor to refer to the ratio of the size of the
effect shown in a graph to the size of the effect shown in thedata. He suggests that lie factors greater than 1.05 or less
than 0.95 produce unacceptable distortion.
A redrawing of
with a lie factor
greater than 8. Another distortion in bar charts results from setting the
baseline to a value other than zero. The baseline is thebottom of the Y-axis, representing the least number of cases
that could have occurred in a category. Normally, this numbershould be zero.
shows the iMac data with
a baseline of 50. Once again, the difference in areas suggestsa different story than the true differences in
percentages. The number of Windows-switchers seems minusculecompared to its true value of 12%.
A redrawing of
with a baseline of
50. Finally, we note that it is a serious mistake to use a line
graph when the X-axis contains merely qualitative variables. Aline graph is essentially a bar graph with the tops of the bars
represented by points joined by lines (the rest of the bar issuppressed).
inappropriately shows a line
graph of the card game data from Yahoo. The drawback to
is that it gives the false impression that the
games are naturally ordered in a numerical way.
A line graph of the number of people playing
different card games on Sunday and Wednesday.
Summary
Pie charts and bar charts can both be effective methods of
portraying qualitative data. Bar charts are better when thereare more than just a few categories and for comparing two or
more distributions. Be careful to avoid creating misleadinggraphs.
Questions & Answers
A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
Receive real-time job alerts and never miss the right job again
Source:
OpenStax, Collaborative statistics (custom online version modified by t. short). OpenStax CNX. Jul 15, 2013 Download for free at http://cnx.org/content/col11476/1.5
Google Play and the Google Play logo are trademarks of Google Inc.
Notification Switch
Would you like to follow the 'Collaborative statistics (custom online version modified by t. short)' conversation and receive update notifications?
