Box-and-whisker plots
Reading Box-and-Whisker Plots Reading Box-and-Whisker Plots
⇐ Use this menu to view and help create subtitles for this video in many different languages.
You'll probably want to hide YouTube's captions if using these subtitles.
- An ecologist surveys the age of about 100 trees
- in a local forest.
- He uses a box and whiskers plot
- to map his data, shown below.
- What is the range of tree ages that he surved?
- What is the median age of a tree in the forest?
- So first of all, let's just...
- let's make sure we understand
- what this box and whiskers plot is even about.
- This is really a way of seeing the spread
- of all of the different data points,
- which is the age of the trees,
- and to also give other information,
- like what is the median and
- where does most... where do most of the ages
- of the trees sit.
- So this whisker part ...
- so you can see this black part is a whisker,
- this is the box,
- and this is another whisker over here.
- The whiskers tell us essentially the spread
- of all of the data.
- So it says the lowest data point in this sample
- is an 8 year old tree
- I'm assuming the axis down here is in years.
- And it says the highest, the oldest tree, right over here,
- is fifty years.
- So if we want the range,
- and we think of range in a statistics point of view.
- We're thinking of the highest data point
- minus the lowest data point.
- So it's going to be 50 - 8.
- So we have a range of 42.
- So that's what the whiskers tell us.
- It tells us that everything falls between 8 and 50 years,
- including 8 years and 50 years.
- Now what the box does, the box starts at ...
- Let me explain it to you this way:
- the mid .. This line over here this is the median
- this right over here is the median.
- And so, half of the ages are going to be less than the median
- we see right over here that the median is 21.
- So this box and whiskers plot tells us
- that half of the trees are going to be less than 21
- and half are older than 21.
- And then these end points, right over here,
- these are the medians for each of those sections.
- So this is the median for all of the trees
- that are less than the real median,
- or less than the main median.
- So this is the middle of all of the trees
- that are less than 21,
- this is the middle age for all of the trees
- that are greater or older than 21.
- And so, these essentially are splitting ...
- We're actually splitting all the data into four groups:
- this we'll call the first quartile,
- so I'll call it Q1 for the first quartile,
- maybe I'll do 1Q.
- This is the first quartile,
- or roughly a fourth of the trees,
- because the way you calculate it sometimes
- a tree ends up in one point or another.
- About a fourth of the trees end up here,
- a fourth of the trees are between 14 and 21,
- a fourth are between 21 and it looks like 33,
- and then a fourth are in this quartile.
- So we call this the first quartile, the second quartile,
- the third quartile and the fourth quartile.
- So to answer the question,
- we already did the range,
- there's a 42 year spread between the oldest and the youngest tree
- and then the median age of a tree in the forest
- is at 21.
- So even though you might have trees that are
- as old as 50,
- the median of the forest is acutally closer
- to the lower end of our entire
- our entire spectrum of all the ages.
- So if you view median as your central tendancy measurement
- it's only at 21 years.
- You can even see it.
- It's closer to the left of the box
- and closer to the left, the end of the left whisker
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
|
Have something that's not a question about this content? |
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
abuse
- disrespectful or offensive
- an advertisement
not helpful
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
wrong category
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site
Share a tip
Suggest a fix
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.