Mathsy stuff/measuring techniques

Question 1

What is accuracy?

Answer 1

how close you observed or measured value is to the correct/real value

Question 2

How can you improve accuracy?
Give an example

Answer 2

changing the experimental technique

e.g. ensure you use the most appropriate size of quadrat in transect measurements. Applies to any equipment really

Question 3

What is reliability?

Answer 3

the consistency in (or your confidence with) a set of measurements

Question 4

How can you improve reliability?

Answer 4

repetition - if repeated results lie close together then the results have high reliability

• taking repeat measurements also helps you identify and omit anomalous results

Question 5

How can you comment on reliability?

Answer 5

• considering spread of results
• considering the closeness of replicates to the mean
• calculating variance, standard deviation, standard error or 95% confidence intervals
• considering the size of range bars or error bars on graphs

Question 6

What is validity?

Answer 6

whether a test actually measures what it sets out to measure

Question 7

How can you comment on validity/improve validity?

Answer 7

• identify factors that are not or cannot be controlled and which may therefore be limiting the validity of the investigation

Question 8

How can water turbidity be measured?

Answer 8

Secchi disk
Turbidity tube
Spectrophotometer

Question 9

How does a Secchi disk work?

Answer 9

• an 8 inch black and white disk attached to a string with measurements on and a weight on the bottom
• it is lowered into the water until you cannot see the pattern any more
• you measure the depth that you can no longer see it
• values that are higher indicate clearer water with a lower concentration of suspended solids, lower values indicate high turbidity with a higher concentration of suspended solids
• this value is converted into NTU (Nephelometric Turbidity Unit)
• low NTU = low turbidity

Question 10

How does a turbidity tube work?

Answer 10

• a clear tube with measurements and a cross/Secchi disk pattern painted in the bottom
• the sample liquid is added to the tube until the cross on the bottom of the tube is no longer visible
• the depth of the sample is then measured to the closest centimetre/millimetre
• this value is converted into NTU (Nephelometric Turbidity Unit)
• low NTU = low turbidity

Question 11

How does a spectrophotometer work?

Answer 11

• its a piece of equipment that shines a beam of light and captures the amount of light that reflects back/scatters or transmits through to measure light penetration
• more scattering/reflection means that the light must have hit something, indicating high turbidity