Data AnalysisDP1a 1c

Frequency charts

Bar graphs histograms

stem & leaf plots

Appropriate Data Displays

BELL Ringer

• Define : Population

• Define: Sample

Population:

• The entire group of people or objects that you want information about

Sample:

The part of the group that is actually surveyed.

Biased versus unbiased questions

Biased slanted

Can be by question or sample

Question is biased if the answer goes one particular way.

A group is biased if it is “prejudiced”towards one particular answer.

TYPES OF GRAPHS

titletitle

J F M A M

Test Scores Out Of 100Stem Leaf

9 2 2 6 88 3 5 7 2 4 6 8 8 96 1 4 4 7 85 0 0 2 8 8

Stem-leaf chart•sort the data from smallest to largest•find the range of the data •consider, typically, 3 significant (or less) digits •each number is broken into a stem value (first 2 digits) and a leaf value (next digit) •plot each leaf against each stem •sort leaves within each stem The resulting stem-leaf chart is similar to a histogram but all the actual data values can be extracted. This allows the user to find certain percentiles.

Frequency chart

•count the number of occurrences of each value

•Interval/Ratio scale frequency chart •divide range of data values in a small

number of equal sized intervals •choose appropriate endpoints for each interval

•decide where values that fall on endpoints will fall •count the number in each interval (tally marks)

Times hands washed

Tally Frequency

0-3 6

4-7 5

8-11 4

12-15 7

Hand Washing Survey

Histogram for Hand Washing Survey

Times hands washed

Tally Freq.

0-3 ||||| | 6

4-7 ||||| 5

8-11 |||| 4

12-15 ||||| || 7

Hand Washing

0-3 4-7 8-11 12-15

7

6

5

4

3

2

1

Choosing appropriate graphs?Circle graph percentages

Line graph Change over time

Histogram Intervals needed

Stem & leaf plot Group data in ordered list

Bar graph Distinct categories

Population

definition characteristics

Examples from your life illustration

Misleading graphsGraphs that are accurate – represent the data but can lead the viewer to different conclusions.

Gap in data

Bars not same width

Colors – some very bright others pale and fade into graph

Scale too small or too large to get an accurate view of the differences between categories. go up by 1’s when data is 100, 125,175

Intervals equal but data spread does not match – data 1, 2, 12, 13,14,23,24,25,29,30,32

Intervals 1-15 16-30 31-45

You are to create two graphs – both will represent the same data and will be accurate; but one will be misleading .