Mathsy stuff/measuring techniques

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

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

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

repetition - if repeated results lie close together then the results have high reliability • taking repeat measurements also helps you identify and omit anomalous results

• 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

whether a test actually measures what it sets out to measure

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

Secchi disk Turbidity tube Spectrophotometer

• 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

• 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

• 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

is the data we have collected what we would expect or is it significantly different?

χ2 = ∑(O – E)2/E

• Dry soil sample • Weigh it • Burn it in a crucible to burn off the organic matter content • Weigh it again • Take the burnt weight from the original and convert it into a percentage

Anemometer on a transect Repeat at different distances along the transect Same heights, same time of day Use a calibrated device Repeat at least 10 times

“Significant at the x level, not significant at y. Can be more than x confident that the result did not occur by chance, so the null hypothesis is rejected at x confidence level” OR “…. can be x confident that the result did occur by chance, so the null hypothesis is accepted at x confidence level”