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Sampling and bias

Sampling and bias for A Level Combined Science AQA Foundation: what it means, how to set the working out, and the questions it is asked in.
  • A Level
  • AQA
  • Combined Science
  • Foundation
  • Spec S4 · S9 · S11
  • 12 min read
  • 7 revision boxes

Introduction

2 boxes
4 min read

What is sampling and bias?

Listen to this box

Transcript

A short spoken summary of sampling and bias and where it is used.

A spoken walk-through of sampling and bias before you read the notes.
Read the units in the question before you start; a converted unit is the most common slip.
The layout below is the one the mark scheme expects.

Diagram showing sampling and bias laid out step by step

The same idea drawn out, so the method is visible.
3 rows

The sampling and bias reference table

The specification wording is precise here, and the mark scheme follows that wording exactly.
Term
Meaning
Example
Common slip
Row 1 column 1
Row 1 column 2
a2+b2=c2a^2 + b^2 = c^2
Row 1 column 4
Row 2 column 1
Row 2 column 2
x2+5x+6=0x^2 + 5x + 6 = 0
Row 2 column 4
Row 3 column 1
Row 3 column 2
34×25\frac{3}{4} \times \frac{2}{5}
Row 3 column 4

Learning

3 boxes
4 steps

How to work with sampling and bias

Work through the method one line at a time and write down what changes at each step.
Worth knowing: 49=7\sqrt{49} = 7.
  1. Read the question and write down what is being asked for.
  2. Set out the working for sampling and bias in the order the method gives.
  3. Substitute the values and simplify.
Start from the definition and substitute the numbers the question gives you.
Simplify one line at a time: a2+b2=c2a^2 + b^2 = c^2.
Answer: ×10\times 10 moves every digit one column left
2 rules

Key facts: Sampling and bias

Check the answer against an estimate before you move on, so a place-value slip is caught here.
The layout below is the one the mark scheme expects.

Diagram showing sampling and bias laid out step by step

The same idea drawn out, so the method is visible.
Worth knowing: a2+b2=c2a^2 + b^2 = c^2.

  • Rule 1

    How sampling and bias behaves in the 1st of the cases the specification names.
    x2+5x+6=0x^2 + 5x + 6 = 0

  • Rule 2

    How sampling and bias behaves in the 2nd of the cases the specification names.
    34×25\frac{3}{4} \times \frac{2}{5}
4 steps

How to work with sampling and bias

Read the units in the question before you start; a converted unit is the most common slip.
  1. Read the question and write down what is being asked for.
  2. Set out the working for sampling and bias in the order the method gives.
  3. Substitute the values and simplify.
  4. Check the answer against an estimate before writing it down.
Start from the definition and substitute the numbers the question gives you.
Simplify one line at a time: ×10\times 10 moves every digit one column left.
Answer: x2+5x+6=0x^2 + 5x + 6 = 0

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Examples

2 boxes
2 marks · worked

Worked example: sampling and bias

Work through the method one line at a time and write down what changes at each step.
Worth knowing: x2+5x+6=0x^2 + 5x + 6 = 0.
1 marks · worked

Practice question 7: ×10\times 10 moves every digit one column left

Read the units in the question before you start; a converted unit is the most common slip.
The layout below is the one the mark scheme expects.

Diagram showing sampling and bias laid out step by step

The same idea drawn out, so the method is visible.

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Common questions

How many marks is sampling and bias usually worth?
Between one and four, depending on how many steps the question asks for.
Is this on the A Level Combined Science AQA Foundation paper?
Yes — it sits in the Programming strand.