← VCE Data Analytics U4O1

Confirming a chart represents the data

A chart whose plotted values, axis scales and categories all match the source data, so it shows the data truthfully and does not mislead the viewer.

Part of: VCE Data Analytics - U4O1 - Development and Evaluation — Module 86

Understanding Confirming a chart represents the data in VCE Data Analytics U4O1

What it does: A bar chart axis that starts at zero keeps bar heights in proportion to the real values, so the chart is representative. A formula comparing a source cell with the chart's data cell returns TRUE when the plotted value matches the table, confirming that value is represented correctly. The chart type must suit the data. Pie charts show parts of a whole, while line charts show trends over time.

Common mistakes: The check should confirm the plotted values equal the table values, so it needs == (equal). != returns True when the chart does NOT match the data. A bar chart axis should start at 0 so bar lengths match the data. Starting at the smallest value exaggerates the differences. It should be axis_start = 0.

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This module's key terms are also in a printable crossword (Modules 85–105) and word search (Modules 63–105).

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Learning

Duo

A bar chart shows Maths = 80, but the source table says Maths = 88. What does this tell you?

The chart is not representative because a plotted value does not match the tableThe chart is representative because the bar is close enough to the table value

Matches

Source total = 250, chart bars add up to 310

↓

The totals do not match, so a value has been plotted wrongly, doubled or added by mistake. Check each bar against the table and correct it.

Applying

Meanings

Term

representative chart

Meaning

A chart whose plotted values, axis scales and categories all match the source data, so it shows the data truthfully and does not mislead the viewer.

Practice

=IF(SUM(B2:B9)=579,"Totals match","Check chart")

Testing

Gaps

=(B2:B9)

Check Answer

Spots

3print(sum(sales), sum(shown))

4match = sales != shown

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Quick Questions

1. A bar chart shows Maths = 80, but the source table says Maths = 88. What does this tell you?

A. The chart is representative because the bar is close enough to the table value

B. The chart is not representative because a plotted value does not match the table ✓

Every plotted value must match the source data exactly. A bar showing 80 instead of 88 means the chart misrepresents the data.

2. A column chart's y-axis starts at 70 instead of 0, which makes a small difference look huge. What should you check?

A. Check the axis start and scale, because a truncated axis can exaggerate differences ✓

B. Nothing needs checking, because the axis start never changes how the data looks

A truncated axis exaggerates gaps between bars. Checking the axis start and scale is part of confirming a chart is representative.

3. A pie chart of sales by category shows slices that add up to 112%. What is the problem?

A. This is fine, because pie chart slices can add up to more than 100%

B. The totals do not add up, so the chart does not match the source data ✓

Parts of a whole must add up to 100%. If they do not, some values or categories are wrong, so the chart is not representative.

4. Your table has 5 categories, but the chart only shows 4. Which action best confirms the chart is representative?

A. Compare the chart categories with the table and add the missing category ✓

B. Leave the chart as it is, because 4 categories are enough

A representative chart includes all the categories in the source data. A missing category hides part of the data from the viewer.

5. Which chart type best suits showing how daily temperature changes across a week?

A. A line chart, because it shows change over time ✓

B. A pie chart, because it shows each day's temperature as a slice

The chart type must suit the data. Pie charts show parts of a whole, while line charts show trends over time.

Match the Pairs

representative chart → A chart whose plotted values, axis scales and categories all match the source data, so it shows the data truthfully

=SUM(B2:B6)=SUM(C2:C6) → A check that the total of the source table equals the total shown in the chart's data, to confirm the totals add up

Check that the chart's axis starts at zero so bar lengths are not exaggerated → Axis minimum = 0

Compare each plotted value with its matching cell in the source table → =B3=D3

Source total = 250, chart bars add up to 310 → The totals do not match, so a value has been plotted wrongly, doubled or added by mistake. Check each bar against the table and correct it.

Pie chart used to show daily temperatures across 30 days → The chart type does not suit the data. A pie chart shows parts of a whole, so a line or column chart should be used to show change over time.

Key Term

representative chart

A chart whose plotted values, axis scales and categories all match the source data, so it shows the data truthfully and does not mislead the viewer.

Fill in the Blanks

1. =SUM(B2:B9)

Hint: Type the function that adds the plotted values so the total can be compared with the chart or source table.

2. =MAX(B2:B9)

Hint: Type the function that finds the largest value, to compare with the tallest bar on the chart.

3. =COUNT(B2:B9)

Hint: Type the function that counts how many numbers there are, to check it matches the number of bars drawn.

4. =IF(SUM(B2:B9)=SUM(C2:C9),"Match","Check")

Hint: Type the function that tests whether two totals are equal and returns one of two messages.

5. =MIN(B2:B9)

Hint: Type the function that finds the smallest value, to see whether the chart's axis start hides or exaggerates differences.

Spot the Error

Question 1

A sales = [12, 18, 9, 15]

B shown = [12, 18, 9, 15]

C print(sum(sales), sum(shown))

D match = sales != shown

E print(match)

Line D — The check should confirm the plotted values equal the table values, so it needs == (equal). != returns True when the chart does NOT match the data.

Question 2

A values = [52, 55, 53]

B axis_start = min(values)

C if axis_start != 0:

D print('Truncated axis')

Line B — A bar chart axis should start at 0 so bar lengths match the data. Starting at the smallest value exaggerates the differences. It should be axis_start = 0.

Question 3

A parts = [40, 35, 25]

B total = sum(parts)

C if total = 100:

D print('Pie adds to 100%')

Line C — A single = assigns a value and is a syntax error in a condition. To check that the pie slices add up to 100 you need the comparison operator ==.

Question 4

A kinds = ['Cat', 'Dog']

B counts = [8, 5, 3]

C ok = len(kinds) == len(counts)

D print(ok)

Line A — The source data has three categories, so the chart needs all three. Leaving out 'Fish' means a category is missing and the chart does not match the data.

Question 5

A chart = 'pie'

B data = 'sales by month'

C suits = chart == 'line'

D print(suits)

Line A — Sales by month is data over time, which suits a line chart. A pie chart shows parts of a whole, so it is the wrong chart type here. It should be chart = 'line'.

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