Drawing Charts

Tools of Quality?

• Histograms• Frequency Graph • Bar Chart• Pie Chart• Line Graph• Scatter Plots• Control Charts

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Basic knowledge for anyone interested in quality, engineering problem solving & systems design

Histogram

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Slices of Pizza

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In statistics, a histogram is a type of graph that shows the distribution of frequencies of data, usually in the form of vertical bars. This type of graph is also commonly called a frequency histogram. In a histogram graph, the height of each bar shows the number of items that fall into that range on the graph.

What is the difference between a bar graph and a histogram?

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In bar graphs are usually used to display "categorical data", that is data that fits into categories. For example suppose that I offered to buy donuts for six people and three said they wanted chocolate covered, 2 said plain and one said with icing sugar.

Histograms on the other hand are usually used to present "continuous data", that is data that represents measured quantity. The data would then be collected into categories to present a histogram.

Frequency Polygon

Easy to draw, just put a mark at the top (in the middle) of each bar and join with straight lines.

• Good for comparing sets of data

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Number of grade ‘C’ or above passes in maths (B band)

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1999 2000 2001 2002 2003 2004 2005 E O Jones

FREQUENCY

YEAR

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A bar graph

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Chocolat Vanilla Strawberr Mint & C Rocky R Bubble G

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How Is the InformationPresented?

• A bar graph is made.

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ChocolateVanillaStrawberryMint & ChipRocky RoadBubble Gum

A pie chart

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Chocolate

Vanilla

Strawberry

Mint & Chip

Rocky RoadBubble Gum

A line graph

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Chocolate Vanilla StrawberrMint & Ch Rocky Ro Bubble G

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A pictograph

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ChocolateVanilla

Strawberry

Mint & Chip

Rocky Road

Bubble Gum

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Scatter Diagrams

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150 400 650

3.5

4

4.5

5

150 400 650

3.5

4

4.5

5

150 400 6503.5

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4.5

5

150 400 650

3.5

4

4.5

5

150 400 650

Positive Correlation

Positive Correlation?

Negative Correlation

Negative Correlation?

No Correlation

Control Charts

Upper Limit

17 inches

Lower Limit15 Inches

E O JonesSmall Pie

X16 inches=