Data Interpretation: Tables, Charts and Decisions

Formulas (2)

• Reading a table: rows, columns, units and totals · Weighted total from a table
  $$\text{total} = \sum (\text{quantity} \times \text{rate})$$
• Bar charts, line graphs and pie charts · Angle of a pie-chart sector
  $$\text{angle} = \frac{\text{value}}{\text{total}} \times 360^\circ$$

Watch out for (3)

• The most items is not the most money
  → Reading a table: rows, columns, units and totals
• A cut-off axis exaggerates differences
  → Bar charts, line graphs and pie charts
• On a distance-time graph, steeper means faster
  → Bar charts, line graphs and pie charts

Formulas (2)

• Mean, median and mode from a frequency table · Mean of a frequency table
  $$\bar{x} = \frac{\sum f x}{\sum f}$$
• Percentage change, share and contribution from data · Percentage change and share
  $$\%\ \text{change} = \frac{\text{new} - \text{old}}{\text{old}} \times 100\% \qquad \text{share} = \frac{\text{part}}{\text{total}}$$

Watch out for (4)

• Divide by the number of values, not the number of columns
  → Mean, median and mode from a frequency table
• The mode and median are values
  → Mean, median and mode from a frequency table
• Largest rise and largest percentage rise are different questions
  → Percentage change, share and contribution from data
• A falling share is not a falling amount
  → Percentage change, share and contribution from data

Reference tables (1)

Watch out for (5)

• The cheapest row usually breaks a condition
  → Combining conditions: filter first, then optimise
• Allow the waiting and task time before choosing the next service
  → Timetables, schedules and time zones
• Convert to one clock before comparing times
  → Timetables, schedules and time zones
• Together is not cause
  → What the data can and cannot support
• Count and rate can move in opposite directions
  → What the data can and cannot support