Download IB Math SL Chapter 20F

Variance and Standard Deviation
IB MATH SL CHAPTER 20F
20F.1 VARIANCE AND STANDARD DEVIATION
Another way to discuss spread of data
 Range and IQR only use two values of data, so
we need a better way to describe the spread.

VARIANCE
STANDARD DEVIATION
Standard deviation is only useful if the distribution
is approximately symmetrical. Most useful if data is
normally distributed (CH 24).
Standard deviation is quoted more than variance.
IQR and percentiles are more appropriate tools for
measuring spread if distribution is skewed.
EXAMPLE 6 P.518
ANSWERS
USING TECHNOLOGY

Enter data into graphing calculator list.
 STAT,
edit 1, clear L1 by moving curser on top of L1
and hit clear enter, enter data, 2nd quit.

Run 1-variable test
 STAT,
CALC, 1-Var Stats, 2nd 1 to get L1, enter
 “1-Var
Stats L1”
USING TECHNOLOGY
What does all this mean?
ANOTHER SUPER FUN EXAMPLE
ANOTHER SUPER FUN EXAMPLE
Answer:
20F.2
SAMPLING FROM A POPULATION
Populations are often too large to gather all
data.
 Thus, a random sample is taken from the
population in hopes it truly reflects
characteristics of the population.
 Samples must be large and unbiased.

NOTATIONS
20F.3 STANDARD DEVIATION FOR GROUP DATA
FYI: For continuous data, or data that has been
grouped in classes, we use the midpoint of the
interval to represent all data in that interval.
EXAMPLE:
EXAMPLE: