Lesson 11 - Types of sampling

Question 1

Sampling definition

Answer 1

Taking measurements of a limited number of individual organisms present in a particular area.

Question 2

Purpose of sampling:

Answer 2

• Abundance: Estimate the number of organisms in an area without having to count them all.
• Measure particular characteristic of an organism.

Question 3

Use of a sample:

Answer 3

Use results to make generalisations or estimates about:

• Number of organisms
• Distribution of species
• Distribution of measured characteristic throughout entire habitat.

Question 4

Two types of sampling:

Answer 4

• Random
• Non-random

Question 5

Random sampling definition

Answer 5

Selective by chance

• Each individual in the population has an equal likelihood of selection.

Question 6

How to complete random sampling:

Answer 6

1. Mark out a grid on the grass using two tape measures laid at right angles.
2. Use random numbers to determine the x coordinate and the y coordinate on the grid.
3. Take a sample at each of the coordinate pairs generated.

Question 7

Non-random sampling definition:

Answer 7

Sample is not chosen at random:

• opportunistic
• Stratified
• Systematic

Question 8

Non-random sampling: opportunistic

Answer 8

• Weakest form of sampling as it may not be representative of population.
• Uses organisms that are conveniently available.

Question 9

Non-random sampling: stratified

Answer 9

• Populations divided into strata based on a particular characteristic. (Male and female)
• A random sample is taken from each of these strata proportional to its size.

Question 10

Non-random sampling: systematic

Answer 10

• Often uses a line or belt transect. –> marks a line along ground between two poles, taking samples at specified points.
• Belt transect provides more information –> two parallel lines are marked and samples are taken of area between lines.

Question 11

Sampling bias

Answer 11

Selection process biased.

• Accident or deliberate.
• Where human involvement in choosing samples is not removed.

Question 12

Chance

Answer 12

The organisms selected may, by chance, not be representative of the whole population.

• Chance can never be removed.
• Effect can be minimalised by using large samples.
• The larger the sample size the more reliable the result.

Question 13

Reliability of sampling:

Answer 13

Never fully representative of organisms present in a habitat.

• Sampling bias
• Chance

Question 14

State the difference between random and non-random sampling:

Answer 14

Random sampling has no human involvement and selects individuals by chance.

Non-random sampling has human involvement and occurs with availability, characteristics or organism distribution within the habitat.

Question 15

Describe how you can increase the likelihood of a sample being a reliable representation of the population as a whole:

Answer 15

1. Increase the sample size.
2. To reduce the effect of chance.
3. Remove human involvement in choosing samples.
4. To remove sampling bias.

Question 16

Which type of sampling would be used to measure how organisms differ throughout the length of a stream.

Answer 16

Systematic:
- Line transect

• Belt transect

To measure how the distribution and change in organisms along the length of the transect.

Question 17

Which type of sampling would be used to measure the distribution of organisms on a school field?

Answer 17

Random sampling

To select grids on the field.