Choosing who to survey: sample and sample size

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. You want to know what the whole school thinks about the canteen menu. Which sample is better?

A Ask 40 students picked from every year level

B Ask only your 4 best friends

2. What is a sample?

A The group of people you actually ask in a survey

B Every single person in the whole school

3. Which statement about sample size is true?

A A bigger sample usually gives more trustworthy data

B A sample of 3 people is just as trustworthy as 60

4. Mia surveys only the students sitting at her lunch table. What is the problem?

A Her sample is too fair, because she knows everyone

B Her sample is not fair, because it only includes friends

5. Your class has 28 students and you want to know their favourite sport. Which is a whole-class survey?

A Ask 10 students chosen at random

B Ask all 28 students in the class

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1sample		AAsking only a few friends gives a biased sample. Friends often think alike, so the results won't match the whole group.
2sample size		Bwhole class = 30 of 30, sample = 20 of 200
3A fair sample asks students from every year level, not only your own friends		CThe group of people you actually ask in a survey, rather than everyone in the whole group.
4Asking the whole class gets everyone's answer, but a sample of 20 out of 200 students is quicker		Dsample = students from Year 7, 8, 9 and 10
5sample = my 3 best friends		ETwo responses is too small to be trustworthy. One unusual answer changes the results a lot.
6sample size = 2, so the results are reliable		FHow many people are in your sample. A bigger sample usually gives more trustworthy data.

Definitions

sample

Fill in the Blanks

Complete each line of code by filling in the missing parts.

=______(B2:B31)

=COUNTA(B2:B31)_COUNTA(A2:A101)

=COUNTA(A2:A101)_COUNTA(B2:B31)

=__(COUNTA(B2:B31)>=30,"Enough","Need more")

=_______(C2:C31,"Friend")

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A total ← 200

B size ← 40

C pick ← random(total, size)

D pct ← total / size * 100

Question 2

A whole ← 30

B sample ← my_mates(whole, 10)

C ask(sample)

Question 3

A class ← 28

B sample ← 38

C IF sample < class THEN

D say("This is a sample")

E ENDIF

Question 4

A responses ← 0

B FOR each student in sample

C responses ← responses - 1

D OUTPUT responses

Question 5

A enough ← 30

B IF responses <= enough THEN

C say("Big enough sample")

D ELSE

E say("Ask more people")

Answer Key

Choosing who to survey: sample and sample size

Section A: Quick Questions

A — Ask 40 students picked from every year level

A — The group of people you actually ask in a survey

A — A bigger sample usually gives more trustworthy data

B — Her sample is not fair, because it only includes friends

B — Ask all 28 students in the class

Section B: Match the Pairs

sample → The group of people you actually ask in a survey, rather than everyone in the whole group.

sample size → How many people are in your sample. A bigger sample usually gives more trustworthy data.

A fair sample asks students from every year level, not only your own friends → sample = students from Year 7, 8, 9 and 10

Asking the whole class gets everyone's answer, but a sample of 20 out of 200 students is quicker → whole class = 30 of 30, sample = 20 of 200

sample = my 3 best friends → Asking only a few friends gives a biased sample. Friends often think alike, so the results won't match the whole group.

sample size = 2, so the results are reliable → Two responses is too small to be trustworthy. One unusual answer changes the results a lot.

Section C: Definitions

sample — The group of people you actually ask in a survey. A bigger, fairer sample gives more trustworthy data than asking only a few friends.

Section D: Fill in the Blanks

=COUNTA(B2:B31)

=COUNTA(B2:B31)/COUNTA(A2:A101)

=COUNTA(A2:A101)-COUNTA(B2:B31)

=IF(COUNTA(B2:B31)>=30,"Enough","Need more")

=COUNTIF(C2:C31,"Friend")

Section E: Spot the Error

D — The percentage of the group you asked is the sample size divided by the whole group, times 100. It should be size / total * 100.

B — Asking only your mates gives a biased sample. The sample should be picked fairly at random: random(whole, 10).

B — A sample is only part of the whole class, so it cannot be bigger than the class of 28. It should be a smaller number such as 8.

C — Each answer collected should add 1 to the count, not subtract. It should be responses ← responses + 1.

B — The sample is big enough when responses reach or pass the target. The check should use >=, not <=.