EMPA: Common Themes

SAMPLE SIZE, REPEATS & ANOMALIES
1. 2< repeats
  1. Anomalies can be identified. Vice versa to check if a result is anomalous REPEAT experiment
  2. More reliable mean
  3. check results concordant (similar)
  4. Minimise effects of variation in data
2. Large sample size
  1. Representative
  2. Allows statistical tests to be conducted
3. data for last 3 tubes more reliable than for 1st 3. Practice in judging when product appears/approximate time of curd appearance known, so able to watch more carefully at that time
4. Accuracy: how close mean is to true value
5. Reliable: little variation in results, approx same. Repeatable- if experiment repeated, similar results
CONFOUNDING (CONTROL/KEEP SAME) VARIABLES
1. TEMPERATURE
  1. If not controlled in investigation, how to find how it could've influenced results
    1. Monitor room temp thru out/ at beginning & end of experiment
  2. Keeping it constant
    1. Water bath: more temp variation in air than water/it keeps test tubes at constant temp
      1. Temp of water bath as reliable as possible: measure temp of bath at beginning & end of reaction period (or more) to assess effect of any temp changes during reaction/to show there was no/little variation in temperature
      2. EQUILIBRATION
        Leave tube 1 in water bath for 5 mins before adding enzyme. To equilibrate /for solution to reach the temp of bath
    2. Monitor with thermometer
    3. use data-logger to record temp
    4. Adjust with hot/cold water
2. pH
  1. Keep constant: use buffer
    1. If 2 enzymes with diff optimum pH, then use 2 buffers
3. Other C variables/precautions/standardisations
  1. Volume/mass
  2. Concentration
  3. Standardise type/category
  4. Time: between readings;duration; mixing
  5. All controlled apart from 1-independent variable
    1. Allows comparison of results/reproduce-able (diff techniques but same results)/repeatable (exact same technique) by someone else
    2. Investigating 1 variable only
  6. No./rate of repeats
  7. Read meniscus at eye level
    1. Same end point each time
LIMITATIONS (UNCONTROLLABLE CONFOUND'N VARIABLES)
1. Difficult to time/measure accurately
2. Diffi to keep temp constant
3. Diffi to decide when product present /formed--subjective
  1. Everyone's judgement diff
4. Theres many variations (creeping in..) in 1 'type'
CONTROL EXPERIMENT (TO COMPARE with effect of independent)
1. YES! shows independent variable causing result , not any other variable.
2. NO! experiment to determine whether result due to independent, nothing else
3. To conduct treat everything same but eliminate/replace independent used in experiment e.g. replace alcohol with H2O
%change/increase in mass/volume/ ratios: COMPARISON as initial diff
1. Analyse class results, student calculates % increase in pulse rate/student. YES: result comparison (as resting pulse maybe diff so accounting all results); NO: exercise not standardised so can't compare
RANDOM TESTING
1. Divide into 2 equal groups
  1. keep control & experimental group 'same' for 1 factor e.g. age, sex, mass
  2. Or divide randomly
    1. which avoid bias/allows statistical analysis
STANDARD DEVIATION
1. BARS suggest about difference..?
  1. If SD bars don't overlap difference significant/more variation in one than the other
  2. Overlapping SD results due to chance
2. WHAT it shows?
  1. SPREAD of measurements around mean/accounts all measurements
  2. how reliable measurements are/mean is
  3. Even without same sample size for each set of measurements, can calculate SD
  4. Large SD: greater spread of data. Smaller SD: bigger central tendency & data concentrated around mean.
ACCURACY
1. measuring time for larger volume drain using larger syringe: MORE ACCURATE as time to drain longer / less effect from stopping / starting timer / smaller percentage error;
  1. using digital timer that measures to 0.0001 sec No/little difference) as effect of stopping / starting timer still has big effect
    1. Judging when all solution has drained subjective / not as accurate as timer
2. Measuring pulse for shorter than 20 secs=>unreliable results. incomplete beats/cycles; Small difference in measurements can produce large difference in pulse rate when multiplied;
3. Length no shorter than instructed
  1. Errors have relatively larger effect/length maybe not long enough to give measurable change
GRAPHS
1. Join points on graph straight lines NOT curve; no INTERMEDIATE values; can't predict rate between plotted values
2. Student said optimum pH for lactase was pH 6.0. Not valid as peak could be anywhere pH 5.5 - 7.5 / should've repeated experiment at appropriate pH
3. Should curve start from 0? NO: Curve shouldn't extend beyond data collected. YES at origin no product formation (in other cases control necessary to deduce this)
  1. EXTRAPOLATE (extend curve)
ETHICS
1. Natural product used--safe i.e.no harmful effects;
  1. No change to lifestyle of participants
  2. Participants healthy, volunteers (own choice)
EVALUATING SUGGESTIONS/NEWSPAPERS
1. Newspaper: taking MCP will mean increased resistance to disease.
  1. Conc not valid: response only observed in mice
  2. Disease organisms not investigated
  3. Not all disease caused by pathogens / cured by antibodies
2. Farmer concluded from graph feeding cows on corn reduces omega-3 fatty acid content in milk. Evaluate conclusion
  1. The graph shows decrease with time feeding on corn (STATE TREND), No control group (-VE)/ may decrease with time than time spent feeding on corn (-VE)
    1. Other named factor may've changed (other factors)
    2. Only one investigation so might not be representative
PLACEBO & DRUG TRIALS
1. placebo juice used to dilute C juice--had same concentration of sugars, minerals & vitamins as C. P juice used instead of H2O...
  1. To maintain constant intake of energy (Otherwise) result may've been due to diff amounts of sugars/minerals/vitamins
  2. So that participants didn't know concentration of juice being used

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EMPA: Common Themes

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	Created by Anna Rattu about 10 years ago