1 Scientific Measurement Practice @dave_lush @UWE_JT9USSJT9-30-2 Scientific Measurement Practice @dave_lush @UWE_JT9

2 Ethos – more than just measurement!It’s about how science works/doing science… Scientific theories seek to explain variation in the world Construct testable hypotheses – experimental design Carry out experiments – scientific measurement Analyse results – statistical analysis Report results – scientific communication Refine theories; go around again, etc, etc Alternate module titles? The Practice & Communication of Science Accounting for Variation

3 Structure Activities… Assessment… Online learning – approx 2h / weekscreencasts, reading, data-handling Collaborate sessions 2 h / fortnight – questions (ask/asked)/discuss/problem solve Practicals (at UWE) Week 7 – the ‘glassbeads’ expt Week 24 – antioxidant analysis; control of respiration Assessment… CC1: 1.5h exam – Jan; 3 online activities in Sem 2?? CW1: Literature review (2000 words, Week 19) CW2: Project report (2000 words, Week 37)

4 Assessment Exams… Coursework…Jan exam short answer, data interpretation, and calculation Sem 2 – via Blackboard (depends on its features) Coursework… Both related to a ‘mini-project’, negotiated individually CW1: Literature review of the topic area CW2: Scientific report… Title/Abstract Introduction (unnecessary, given the CW1/Lit Rev) Methods Results/analysis Discussion/conclusions References Firm up topics by Week 15; data finalised Week 26

5 Intro to Prac #1 – The Glassbeads ExptAim… How the answers you get when you observe nature are influenced by randomness and measuring system used Challenge… Determine overall vol of a spoonful of glass beads placed in a 25 ml volumetric flask – without removing beads Equipment… Burette, micropipettes, water, electronic balance, spectrophotometer, measuring cylinder, water-soluble dye, empty 25 ml volumetric flask (no beads) 10 min activity, now… Think of 4 methods, using above equipment, to measure vol of beads

6 Intro to Prac #1 – The 4 MethodsVol by addition… Add water from burette to fill flask to 25 ml Bead vol is 25 ml – vol added Vol by subtraction… Fill flask to 25 ml mark with water, decant into grad cylinder Bead vol is 25 ml – vol in grad cylinder Vol by dilution analysis… Add same amount of dye solution to beads flask and empty flask, make both up to 25 ml mark Decant from each, measure absorbance, do some maths  Vol by indirect weighing… Weigh flask/beads, add H2O to 25 ml, weigh again, do maths Which method is the ‘reference’ method?

7 Intro to Prac #1 – The ResultsVariation between the 4 methods reflects 2 things… Random error – eg pipetting etc (annoying!) Systematic effect of the measuring method (interesting!) If you do experiment once… You can say absolutely nothing apart from ‘this is what I got’ If you do it multiple times (eg we will do it x5)… You can use the power of statistics to start to tease the random and systematic effects apart But, regardless of how good a scientist you are… You can never, ever, ever completely differentiate them! This has the most profound implication… All measurements are ‘corrupted’ by things we cannot control Science can only assign probabilities to things, not certainties This means all science is provisional – potentially falsifiable

8 Intro to Prac #1 – The Follow-upBy end of prac session today… Work out the five estimates of beads volume for each of the four methods Choose which is the ‘reference’ method Between now and Week 9 Collaborate session… Use online tutorial to test if there are significant differences between the reference method estimates and each of the other three methods Think about your results in terms of accuracy, precision and (maybe) sensitivity Accuracy…? Precision…? Sensitivity…?