Sampling involves taking measurements of individuals, selected from the population of organisms which is being investigated. However sometimes, the effects of chance takeover, and the sample lacks representitiveness. There are several reasons why they might not be, including:
- Sampling bias - the selection process may be biased. The investigators may be making unrepresentative choices, either deliberately or unwittingly.
- Chance - even if sampling bias is avoided the individuals chosen may, by pure chance, not be representative.
The best way to prevent sampling bias is to eliminate, as far as possible, any human involvement in choosing the samples.
This can be achieved by carrying out random sampling. This can be done by:
- divide the study area into a grid of numbered lines
- using random numbers from a table or generated by a computer, obtain a series of coordinates.
- Tae samples at the intersection of each pair of coordinates.
Arises when scars form on the epithelium of the lungs, causing them to become irreversibly thickened.
To diffuse respiratory gases the lining of the alveoli need to be thin. This means suffers of PF have the following symptoms:
- Shortness of breath - the air space in the lungs is being taken up by the scar tissue, which decreases the volume of air that can occupy the lungs at a given time. Also, the elasticity of the lungs is reduced, and this results in suffers being unable to maintain a diffusion gradient.
- Chronic, dry cough - fibrous tissue creates an obstruction in the airways of the lungs.
- Pain and discomfort in the chest - consequences of pressure, and hence damage, from the mass of fibrous tissue.
- Weakness and fatigue - results from the reduced oxygen intake. The release of cellular respiration is reduced, and so is ATP production, leading to tiredness.