Box Plots

Question 1

What is an outlier?

Answer 1

Any value that is more than 1.5 times the IQR below the lower quartile OR more than 1.5 times the IQR above the upper quartile

Question 2

What is the formula for finding an outlier?

Answer 2

A value is an outlier if…

value < Q1 - 1.5 * IQR
or
value > Q3 + 1.5 * IQR

Question 3

What numbers are needed in a box plot

Answer 3

minimum, lower quartile (Q1), median, upper quartile (Q3), maximum

Question 4

How does a box plot break up data?

Answer 4

A box plot breaks data into quartiles. (25% of the data points are in each quartile).

Question 5

If a box plot represents the heights of 200 people, how many people have heights below the Q1 value?

Answer 5

25% of 200 = 200/4 = 50.

This means 50 people must be in each quartile.

Therefore, 50 people have heights below the Q1 value.

Question 6

How do you calculate the interquartile range (IQR)?

Answer 6

IQR = Q3 - Q1

Question 7

How do you find the Q1, median, and Q3 values on the calculator?

Answer 7

1. Enter data (stat, enter).

If it is just a list of data, put all the data into L1.

If the data is from a frequency table, put the data values in L1 and the frequencies in L2.

2. 1-var-stats (stat, CALC, 1: 1-Var Stats)

If the data was from a list, leave freqList empty.

If the data was from a frequency table, put in L2 (2nd, 2) for freqList.

Question 8

Is this box plot symmetrically distributed, skewed left, or skewed right?

Answer 8

skewed right

this means that extreme high values are pulling the mean higher than the median

Question 9

Is this box plot symmetrically distributed, skewed left, or skewed right?

Answer 9

no skew (symmetrical distribution)

Question 10

Is this box plot symmetrically distributed, skewed left, or skewed right?

Answer 10

skewed left

this means that extreme low values are pulling the mean lower than the median