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Data and Society 9-12 / Week 04 / Friday
5/6
Week 04 · Collecting and Recording

Friday

Impact Friday: One source is rarely enough
// One row per member, one column per question
⏱ about 20 min

Friday: Impact Friday: One Source Is Rarely Enough

The collection week is over. Comet pins the Q2 frequency table to the wall. "Evening wins! We should add longer evening hours."

Wren studies the table. "Forty members answered. The Commons has 120. What do you notice?"

Comet frowns. "We only heard from a third of them."

Keeper Ines lifts a thick book from the desk. "This is the sign-in book. Every member writes a usual visit time when they join."

Nova hovers between the table and the book. "Would you like a hint?" she asks. "You also have the door count from Saturday."

"Three sources," Wren says. "Maybe together they tell us more than one alone."

Combining sources

Often, a single source does not hold all the data needed to draw a conclusion. You may need to combine data from a variety of sources.

The U.S. Census Bureau collects some data directly from people, through the censuses and surveys it runs.

It also combines other kinds of data with its survey and census data.

The crew can do the same at a small scale.

SourceWhat it holdsHow many
Commons Count surveyAnswers to Q1 to Q640 members
Sign-in bookEach member's usual visit timeAll 120 members
Saturday door countPeople through the door each hour95 entries in one day
Usual visit timeSign-in book (members)Survey Q2 (answers)
morning308
afternoon3010
evening3615
weekend247
Total12040

This is made-up data from the Commons Count story.

WHICH SOURCE HELPS?
  • Read the question.
  • Tap your answer.
How many members usually visit in the evening, counting everyone?
What is 30 plus 30 plus 36 plus 24?
Which source shows what members want the Commons to add?

Combine with care

Combining sources can give a fuller picture. It also needs care.

Last week you learned that scattered bits of data can be combined to learn about one person.

So the crew combines totals only, such as 36 evening members. They never match a survey row to a name in the sign-in book.

StatementTrue or false?
A single source always holds all the data needed for a conclusion.?
The Census Bureau combines other kinds of data with its survey and census data.?
The crew compares totals, not names, across the survey and the sign-in book.?
Combining many sources can never reveal anything about one person.?
WHY THIS EXERCISECombining sources helps you reach better conclusions, and doing it carefully protects people.

Week review

  1. A data sheet has one row per member and one column per question.
  2. A column's group totals must add up to the number of rows.
  3. Choosing how often to sample trades detail for storage.
  4. A tally becomes a frequency table, and its total is a built-in check.
  5. Metadata are data about data. Changing them does not change the answers.
  6. One source is rarely enough, so combine sources with care.
PUT THE RECORDING STEPS IN ORDER
  • Tap a card.
  • Then tap its spot.
1First
2Next
3Then
4Last
WEEK CHECK
  • Read the question.
  • Tap your answer.
Counting every 15 minutes instead of every hour gives what?
Which is metadata for a Commons Count sheet?
On paper, sketch three boxes for the survey, the sign-in book and the door count, with arrows to one box labeled conclusion.

What a week, data analyst. Tomorrow is Mission Quest: a window count of your own, with metadata on top.

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