| Exam Board | OCR |
|---|---|
| Module | S2 (Statistics 2) |
| Session | Specimen |
| Marks | 5 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Data representation |
| Type | Critique given sampling method |
| Difficulty | Easy -1.2 This is a straightforward sampling methods question requiring recall of basic sampling theory definitions and standard techniques. Students need only identify that pin-sticking creates bias (larger gardens more likely selected, same house can be selected multiple times) and suggest systematic/stratified sampling from a numbered list—all standard textbook material with no problem-solving or calculation required. |
| Spec | 2.01c Sampling techniques: simple random, opportunity, etc |
| Answer | Marks | Guidance |
|---|---|---|
| - Some regions of the map numbered likely | B1 | For stating one valid relevant reason |
| B1 | For stating a second valid relevant reason |
| Answer | Marks | Guidance |
|---|---|---|
| Select the sample using random numbers | B1 | For stating or implying a sampling frame |
| B1 | For numbering the sampling units | |
| B1 | For referring to use of random numbers |
(i) Reasons for bias may include:
- Larger properties more likely to be picked
- Some regions of the map numbered likely | B1 | For stating one valid relevant reason
| B1 | For stating a second valid relevant reason
(ii) Make a list of all the houses in the neighbourhood
Number the houses from 1 upwards
Select the sample using random numbers | B1 | For stating or implying a sampling frame
| B1 | For numbering the sampling units
| B1 | For referring to use of random numbers
**Total: 5 marks**
---2 A certain neighbourhood contains many small houses (with small gardens) and a few large houses (with large gardens). A sample survey of all houses is to be carried out in this neighbourhood. A student suggests that the sample could be selected by sticking a pin into a map of the neighbourhood the requisite number of times, while blindfolded.\\
(i) Give two reasons why this method does not produce a random sample.\\
(ii) Describe a better method.
\hfill \mbox{\textit{OCR S2 Q2 [5]}}