11.2 Types of Sampling

Question 1

What is sampling?

Answer 1

Taking measurements

of a limited number of individuals

present in a particular area

Question 2

Why is sampling used?

Answer 2

it is difficult/impossible to count all of the organisms in an area

so sampling studies a sample and assumes it to be representative for whole area

Question 3

In what 2 ways can sampling be used?

Answer 3

• Estimate abundance of organisms present in an area
• Measure a particular characteristic
  
  • E.g height of grass

Question 4

What are the 2 types of sampling?

Answer 4

RANDOM - each individual in population has equal probability of selection.

NON-RANDOM - sample is not chosen at random.

Question 5

What is the difference between random and non-random sampling?

Answer 5

Random sampling: every individual in population has equal chance of being sampled.

Non-random sampling: some individuals have a greater chance at being sampled than others.

Question 6

What are the different types of non-random sampling?

Answer 6

• OPPORTUNISTIC - uses organisms most conveniently available. weakest form.
• STRATIFIED - population divided into strata based on a particular characteristic. Random sample taken from each strata proportional to size.
• SYSTEMATIC - different areas of habitat are identified & sampled separately.
  
  • E.g using line transect or belt transect

Question 7

What is opportunistic sampling?

Answer 7

Type of sampling

which uses organisms which are most conveniently available

(weakest form)

Question 8

What is stratified sampling?

Answer 8

Type of sampling

which divides the population into strata based on a characteristic,

& taken random samples from each strata

proportional to size

Question 9

What is systematic sampling?

Answer 9

Type of sampling

which identifies & samples different areas of a habitat

separately.

e.g using line transect or belt transect.

Question 10

What does using a line transect involve?

Answer 10

1. Line marked along the ground.
2. Samples taken at specified points.

Question 11

What does using a belt transect involve?

Answer 11

1. 2 parallel lines marked on the ground, some distance apart.
2. Samples taken at specified points between the lines.

Question 12

What are the reasons for which a sample will never be entirely representative of the organisms present in an area?

Answer 12

• SAMPLING BIAS
  
  • e.g choosing to place a transect in an area with many flowers as opposed to an area with few.
  • effect can be minimised using random sampling.
• CHANCE
  
  • By chance, the organisms chosen are not representative of the whole.
  • effect can be minimised by using large sample size.

Question 13

State & explain which type of sampling should be used to study:

a. how organisms differ throughout the length of a stream.
b. the distribution of organisms on a school field.

Answer 13

a. SYSTEMATIC - transects take samples at regular intervals, so can see how organisms differ along stream/transect.

b. RANDOM - environment is uniform. reduced sample bias.

Question 14

Decreasing the bias & increasing the sample size of a sampling technique increases the ____.

Answer 14

reliability