Zusammenfassung der Ressource
EMPA: Common Themes
- SAMPLE SIZE, REPEATS & ANOMALIES
- 2< repeats
- Anomalies can be identified. Vice versa
to check if a result is anomalous
REPEAT experiment
- More reliable mean
- check
results
concordant
(similar)
- Minimise effects of variation in data
- Large sample size
- Representative
- Allows statistical tests to be conducted
- 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
- Accuracy: how close
mean is to true value
- Reliable: little variation in results,
approx same. Repeatable- if
experiment repeated, similar results
- CONFOUNDING (CONTROL/KEEP SAME) VARIABLES
- TEMPERATURE
- If not controlled in
investigation, how to find
how it could've influenced
results
- Monitor room temp thru out/ at
beginning & end of experiment
- Keeping it constant
- Water bath: more temp variation in air than water/it
keeps test tubes at constant temp
- 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
- EQUILIBRATION
- Leave tube 1 in water bath for 5 mins before adding enzyme. To
equilibrate /for solution to reach the temp of bath
- Monitor with
thermometer
- use data-logger to
record temp
- Adjust with hot/cold water
- pH
- Keep constant: use buffer
- If 2 enzymes with diff
optimum pH, then use
2 buffers
- Other C
variables/precautions/standardisations
- Volume/mass
- Concentration
- Standardise type/category
- Time: between readings;duration;
mixing
- All controlled apart from 1-independent variable
- Allows comparison of results/reproduce-able (diff techniques but
same results)/repeatable (exact same technique) by someone else
- Investigating 1 variable only
- No./rate of repeats
- Read meniscus at eye level
- Same end point each time
- LIMITATIONS (UNCONTROLLABLE
CONFOUND'N VARIABLES)
- Difficult to time/measure accurately
- Diffi to keep temp constant
- Diffi to decide when product present /formed--subjective
- Everyone's judgement diff
- Theres many variations (creeping in..) in 1 'type'
- CONTROL EXPERIMENT (TO COMPARE with effect of independent)
- YES! shows independent variable causing result , not any
other variable.
- NO! experiment to determine
whether result due to independent,
nothing else
- 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
- 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
- Divide into 2
equal groups
- keep control & experimental group
'same' for 1 factor e.g. age, sex,
mass
- Or divide randomly
- which avoid bias/allows statistical analysis
- STANDARD DEVIATION
- BARS suggest about difference..?
- If SD bars don't overlap difference
significant/more variation in one than the other
- Overlapping SD results due to chance
- WHAT it shows?
- SPREAD of measurements around mean/accounts all
measurements
- how reliable
measurements
are/mean is
- Even without same sample size for each set of measurements, can calculate SD
- Large SD: greater spread of data. Smaller SD: bigger central tendency & data concentrated around mean.
- ACCURACY
- 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;
- using digital timer that measures to 0.0001 sec
No/little difference) as effect of stopping /
starting timer still has big effect
- Judging when all solution
has drained subjective / not as
accurate as timer
- 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;
- Length no
shorter than
instructed
- Errors have relatively larger
effect/length maybe not long
enough to give measurable
change
- GRAPHS
- Join points on graph
straight lines NOT curve; no
INTERMEDIATE values; can't predict
rate between plotted values
- 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
- 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)
- EXTRAPOLATE (extend curve)
- ETHICS
- Natural product used--safe i.e.no harmful
effects;
- No change to lifestyle of participants
- Participants healthy, volunteers (own choice)
- EVALUATING SUGGESTIONS/NEWSPAPERS
- Newspaper: taking MCP will mean
increased resistance to disease.
- Conc not valid: response
only observed in mice
- Disease
organisms not
investigated
- Not all disease caused by pathogens / cured by
antibodies
- Farmer concluded from graph
feeding cows on corn reduces
omega-3 fatty acid content in milk.
Evaluate conclusion
- 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)
- Other named factor may've
changed (other factors)
- Only one investigation so
might not be representative
- PLACEBO & DRUG TRIALS
- placebo juice used to dilute C juice--had same concentration of
sugars, minerals & vitamins as C. P juice used instead of
H2O...
- To maintain constant intake of energy (Otherwise) result may've been due to diff
amounts of sugars/minerals/vitamins
- So that participants didn't know
concentration of juice being used