Rullst AcademyRullst Academy/Lesson
Data, probability and statistics I · Lesson 02 / 12

Check the data before calculating

Record B6 has no duration. Turning it into zero would make the route look faster. Investigation starts by understanding what is recorded and what is missing.

Learning paths16 min

Let's discover together

  1. 1

    The Missions example has 12 rows, 11 known durations and one missing value. Zero is a measurement; a blank means “we do not know”. The workshop excludes missing values from numerical calculations and reports their count.

  2. 2

    Two records may share a duration. Two records with the same id need investigation: was the same delivery repeated, or was the identifier wrong? The workshop rejects duplicate ids rather than silently choosing a row.

  3. 3

    This workshop uses a simple CSV format: id,group,minutes; groups A/B; decimal point; duration from 0 to 1440, with up to two decimal places. This limit is an exercise rule, not a statistical law. Quoted fields and decimal commas are unsupported.

  4. 4

    Duplicate an id and try analyzing; read the line number in the error. Correct it and compare blank B6 with B6 equal to zero. Record the effect before returning to the original data. Do not invent a value just to improve the result.

  5. 5

    If the slowest deliveries are the ones missing records, analyzing only known values may distort the conclusion. Reporting missingness is necessary; it does not guarantee the distortion has disappeared.

Evidence lab

Experiment with fictional deliveries at Aurora station. Analysis runs in this browser. Nothing entered here is sent to the server.

The workshop resets when you leave or reload. Download data and report to keep your work, or send the report to the activity editor, which keeps a draft in this browser. Completion and XP belong to the account.

Header id,group,minutes; one delivery per row; unique id; groups A/B; decimal point; duration 0–1440 with up to two decimal places. Blank means unknown. Up to 100 rows. No quotes or decimal commas. Use invented data.

Selection uses the entered table, including missing values. A draw does not guarantee representativeness. The same seed reproduces selection; it cannot recover cases outside the table.

Make a prediction and analyze the table.

Virtual bag: model with replacement

There are four equally likely tokens; choose how many are blue. Each token returns before the next draw. This is a deterministic simulation, without prizes, money or real observations.

Repeating the seed repeats the sequence. More draws do not guarantee a closer result in every run and do not validate the real-world model.

Two rules, the same accuracy

Ten fictional cases: nine normal and one failure. Rules defined for this example; no AI training or real equipment testing. Same number correct, different consequences.

Two rules, the same accuracy
RuleCorrect / totalMissed failuresFalse alarms

Your investigation report

Official links and next step

✦
YOUR MISSION

Distinguish zero, missingness, duplication and unit errors without discarding evidence.

Now it's your turn

Discovery workshop

Predict, check, explain

Distinguish zero, missingness, duplication and unit errors without discarding evidence.
Build your answers and check when you are ready.
A moment to understand

What should you do with an unknown duration?

I need a hint

Missingness tells us something about collection. Changes need reasons and a record; equal values do not prove duplication.

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Take it with you

Create six deliveries with one missing duration and two equal durations. Show how many values enter the mean and explain what additional information would help assess missingness.

At your own pace

My files and GitHub

Every lesson can become your own record: code, notes or a practice plan. Saving a file to GitHub is optional and does not change your XP.

Student guide

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AI can make mistakes. Check the lesson material.