Lesson 2 2 Statistics Honors What is a

Lesson 2. 2 Statistics Honors

What is a stem-and-leaf plot? • A T-chart that is used to show numeric data and the distribution of numbers

Why would I want to use one? • It displays a lot of numbers in a neater, cleaner, and organized way. • It makes it easier to see how spread out the numbers are • It is easier to identify outliers

Reading a Stem-and-Leaf Plot (how to analyze and make inferences)

Things you need to know… • Stems – The stems include the digits in the tens place and higher (sometimes the units place too, if data includes decimals) – The top of the stem includes all but the last digits of the smallest number – The bottom of the stem includes all but the last digit of the largest number – Your stems need to include ALL consecutive numbers in between—even if there is no data for it.

Things you need to know… • leaves – The leaves are always from the LAST digit from your data (usually ones place) – The leaves need to be organized from least to greatest – You can have multiples of the same digit per line (interval)

What does it look like? The stem-and-leaf plot below shows the number of students enrolled in a dance class in the past 12 years. The number of students are 81, 84, 85, 86, 93, 94, 97, 100, 102, 103, 110, and 111. 8 | 4 means 84

Should I skip numbers in my stem? You HAVE TO include all of the consecutive numbers from the first stem until the last one. No! Notice how 6, 7, and 10 have no data next to them. It means that no countries reported sixties, seventies, or one hundreds of infant deaths. You CANNOT put a zero in the leaf spot because that implies that you have data for that stem—which you don’t. This chart shows the number of infant deaths per 1, 000 live births, of countries in Western Africa.

Making a Stem-and-Leaf Plot

This stem-and-leaf plot shows points that students received on a science quiz. Stem Leaves 4 5 6 7 8 9 10 0 6 1 3 0 2 0 9 8 4 5 5 6 0 9 9 777 68 78 40 49 61 64 73 75 80 85 87 49 67 76 56 67 78 58 67 88 92 96 100 59 100

Finding the Range, Mode, Median, and Mean

Range= biggest number – smallest number 40 is the smallest number Stem Leaves 40 61 73 80 85 4 099 75 49 64 87 5 689 100 – 49 40 = 60 76 67 88 6 The 1 4 range 7 7 7 for this data set is 60 points. 7 3568 78 56 67 92 100 is the 8 0 5 7 8 largest 96 number 58 67 9 26 100 59 10 0 0 This stem-and-leaf plot shows points that students received on a science quiz. 100

Finding the Median Start counting (the with this leaf! Stem Leaves middle number) 40 61 73 80 Leaf number 85 12… This is 75 49 I have 6423 leaves. If I the halfway point!divided that in half, 87 I 4 099 5 689 76 49 would 67 be th number end up with 88 23 ÷ 2 = 11. 50 the 12 will our median. 6 14777 The twelfth number is 73. 11. 5. This is. This my median. means 7 3568 56 that the 67 12 th 78 92 number is my median. 8 0578 96 58 67 9 26 100 59 10 0 0 100 This stem-and-leaf plot shows points that students received on a science quiz.

Finding the Mode (the number that shows up most) Stem Leaves You have more 7 s than 9 s or 0 s. 40 means 61 That 67 is your mode. 73 80 85 4 099 75 49 64 For the 5 6 mode, 8 9 look at each row of leaves separately. 87 76 67 underline If you see more than one of 49 a number, it. 6 After 1 looking 4 7 7 at 7 all your rows, pick the underlined 88 digits. 78 7 3 5 number 6 8 that has the 56 most 67 92 8 0578 96 58 67 9 26 100 59 10 0 0 100 This stem-and-leaf plot shows points that students received on a science quiz.

Finding the Mean (the average) Stem Leaves 4 5 6 7 8 9 10 0 6 1 3 0 2 0 99 89 4777 568 578 6 0 Add up all the data: 40 + 49 + 56 + 58 59 + 61 + 64 + 67+ 73 and so on. Your total is 1667. This stem-and-leaf plot shows points that students received on a science quiz.

Finding the Mean (the average) Stem Leaves 4 5 6 7 8 9 10 0 6 1 3 0 2 0 99 89 4777 568 578 6 0 We have 23 leaves. Divide your sum by 23. 1667 ÷ 23 = Mean: Approximately 72. 48