Quiz 2.1

Clear your desk except for a pencil & calculator!

Warm Up

1) Find the mean & median for this data set: 7, 6, 5, 8, 10, 20, 4, 3

2) Which measure of center, the mean or median should be used to describe the data set? Why?

HW Check 2.4

You have 30 seconds to link together as many paper clips

as possible!

Given our class data:

1)Create a frequency table2)Create a histogram3)Describe the distribution

Measures of Spread: Standard Deviation

Describing Data

Two ways to describe data:• Graphically

Dot plotHistogram– Boxplot

• Numerically– Measures of Center: Median and Mean– Measures of Spread

Measures of Spread

• Range

• Interquartile Range (IQR)

• Standard Deviation

How much do values typically vary from the center?

Consider the following test scores:

Who is the best student?How do you know?

Student Test 1 Test 2 Test 3 Test 4

Johnny 65 82 93 100

Will 82 86 89 83

Anna 80 99 73 88

So who is the best?!

Sometimes you need too look at more information than the measure of center…

So we look at the SPREAD…

Measures of Spread

One-Variable:RangeInterquartile Range (IQR)Standard Deviation

How much do values typically vary from the center?

Range To find the range of a set of data you take the largest value in the data set and subtract the smallest number in the data set

BIG # - small # = range

Lets focus on STANDARD DEVIATION

Standard deviation measures the dispersion of data.

The greater the value of the standard deviation, the further the data tends to be dispersed from the mean.

Luckily, we can find the standard deviation on the calculator.

Back to our students . . .

Lets calculating each of their Standard Deviations

Student Test 1 Test 2 Test 3 Test 4

Johnny 65 82 93 100

Will 82 86 89 83

Anna 80 99 73 88

Steps

Step 1: Enter the height data in L1.

Commands: STAT EDIT (Use 2nd QUIT to exit)

Step 2: Find your “best friend” in this unit Commands: STAT CALC 1: 1-Var Stats Enter

What do they all mean…

MeanThe sum of your data

Ignore thisStandard Deviation Ignore this

Number of data entries

Who is the best student?How do you know?

Student Test 1 Test 2 Test 3 Test 4 TestAverage

Standard Deviation

Johnny 65 82 93 100 85 13.2

Will 82 86 89 83 85 2.7

Anna 80 99 73 88 85 9.7

Now calculate the standard deviation of each and discuss…

HW 2.5