, 1
Unit 3 Basic Principles
m m m
❖ Outline of Any Experiment:
m m m
1- Independentm variable:m them factorm youm changem ex.m temperature:
2- Dependentm variable:m them factorm youm measure
ex.mratemofmthemreactionm/massmofmproduct.m(malwaysmincludemSImunit)
m 3-
m Controlledm variablesm keptm constant.(form /m ensures*m Validity)m(no
tmincrease*mvalidity)m.mTheymaremfactorsmthatmcanmaffectmyourmresults.
-Youm needmtom givem (mwheneverm possible)
a--Examplesm ofm controlledm variables.m (+/-m suggestedm values).
b--Howm tom controlm (apparatus).
c--Effectm onmthemresultsm ifm notm controlledm (mobligatoryminm unitm 6m).
-Mentionm controlledm variablesm in:
a- organism:m (samem agem ,m speciesm ,mass,gender)
b- experiment:m ex.m samem pH,m volumem andm concentrationm ofm (enzyme).
c- surroundingm conditions:m (temperature,m lightm intensity)
d- othersm :msamemtypem andmmassm ofm foodm providedm tom anmorganism.
4- Timemscalem:m suitablem tom showm them expectedm results.
5- Replications:mMinimumm3mtimesmatmEACH….m(
Formreliability,mNOTmtomincreasemxxxmreliability)!
-(tom spotm anomaliesm ,m minimisemthem effectm ofm individualm variations,)
-
tomcalculatemthemmeanm,mshowmvariability,mSD,mandmallowmstatisticalmanalysis).m
6-
m Control:m,mDefinition:mIdenticalmexperiment,mwithmidenticalmapparatusmandmc
onditions,mwithoutm themfactormyoumaremtestingm(ex.mwithoutmenzyme).
- Purposemofmthemcontrol:mAllowsmcomparisonm–
(mEnsures*mVALIDITY)mtombemsuremthatmyourmresultsmaremreallymduemtomthismf
actorm&mnomothermfactor.
,2
1
, 3
e.g..m Experimentm resultm =m50maum ,,mcontrolmresultm =mzerom au
Actualm resultm ofm experimentm is: 50m –mzerom=m50mau.
e.g.m Experimentm result = 50mau. Controlmresultm =m 4mau.
Actualmresultmofm experimentm is:m 50m –m4m =m46m au.
❖ Validitym:mHowm TRUE/correctm yourm resultsm are??m Thism ism achievedm by:
1- Keepm allm controlledm variablesm constant.
2- Usem am controlmtom compare.
3- Choosem them correctm accuratem instrumentm tom measurem yourm parameter.
4- Nonm overlappingm errorm bars→m SIGNIFICANTm differencem /correlation.
❖ Reliability:m(mCanm youmtrustmthemresults)m?
1- Largemsamplem sizem (m individualsm /m repetitions)m tom bem representative.
Alsom anomaliesm canm bem identifiedm andm excluded.
2- m Lowm Variability:m Consistentm /similar/m closem resultsm ofm repetitions,
/clusteredmaroundmthem meanm →m SmallmSDm/m narrowmrangem/merrormbars.
3- mNonmoverlappingmerrormbars→mSIGNIFICANTmdifferencemormcorrelation.
4-mRepeatablembymothermscientists,mgivingmthemsame/similarmresults.
m
NB:m(repeatingmdoesmNOTmmakemyourmmeasurementsmmoremreliable,mitmjust
m helpsmyoumtomspotmandmremovemanomalies,massesmandmjudgemthemdegreemo
fmvariability,mhencemreliability!)
• Randomm error:m Unpredictablem ,m occasionalm errorm inm one*m orm morem ofm th
emmeasurements,musuallymcausedmby:
1-
m problemminmthemcontrolledmvariablesm,morm
2m-inaccurateminstrument.
-Ex.m whenm weighingm yourself,m andmstandingm differentlym onm them scale,
orm lookingm atm them levelm ofm am liquidm eachm timem fromm am differentm angle,m or
m difficultyminmstandardisingmthempressuremormforcemapplied.
-Correctedm bym :m Performingm manym repetitions,m excludem them anomalies.
2
Unit 3 Basic Principles
m m m
❖ Outline of Any Experiment:
m m m
1- Independentm variable:m them factorm youm changem ex.m temperature:
2- Dependentm variable:m them factorm youm measure
ex.mratemofmthemreactionm/massmofmproduct.m(malwaysmincludemSImunit)
m 3-
m Controlledm variablesm keptm constant.(form /m ensures*m Validity)m(no
tmincrease*mvalidity)m.mTheymaremfactorsmthatmcanmaffectmyourmresults.
-Youm needmtom givem (mwheneverm possible)
a--Examplesm ofm controlledm variables.m (+/-m suggestedm values).
b--Howm tom controlm (apparatus).
c--Effectm onmthemresultsm ifm notm controlledm (mobligatoryminm unitm 6m).
-Mentionm controlledm variablesm in:
a- organism:m (samem agem ,m speciesm ,mass,gender)
b- experiment:m ex.m samem pH,m volumem andm concentrationm ofm (enzyme).
c- surroundingm conditions:m (temperature,m lightm intensity)
d- othersm :msamemtypem andmmassm ofm foodm providedm tom anmorganism.
4- Timemscalem:m suitablem tom showm them expectedm results.
5- Replications:mMinimumm3mtimesmatmEACH….m(
Formreliability,mNOTmtomincreasemxxxmreliability)!
-(tom spotm anomaliesm ,m minimisemthem effectm ofm individualm variations,)
-
tomcalculatemthemmeanm,mshowmvariability,mSD,mandmallowmstatisticalmanalysis).m
6-
m Control:m,mDefinition:mIdenticalmexperiment,mwithmidenticalmapparatusmandmc
onditions,mwithoutm themfactormyoumaremtestingm(ex.mwithoutmenzyme).
- Purposemofmthemcontrol:mAllowsmcomparisonm–
(mEnsures*mVALIDITY)mtombemsuremthatmyourmresultsmaremreallymduemtomthismf
actorm&mnomothermfactor.
,2
1
, 3
e.g..m Experimentm resultm =m50maum ,,mcontrolmresultm =mzerom au
Actualm resultm ofm experimentm is: 50m –mzerom=m50mau.
e.g.m Experimentm result = 50mau. Controlmresultm =m 4mau.
Actualmresultmofm experimentm is:m 50m –m4m =m46m au.
❖ Validitym:mHowm TRUE/correctm yourm resultsm are??m Thism ism achievedm by:
1- Keepm allm controlledm variablesm constant.
2- Usem am controlmtom compare.
3- Choosem them correctm accuratem instrumentm tom measurem yourm parameter.
4- Nonm overlappingm errorm bars→m SIGNIFICANTm differencem /correlation.
❖ Reliability:m(mCanm youmtrustmthemresults)m?
1- Largemsamplem sizem (m individualsm /m repetitions)m tom bem representative.
Alsom anomaliesm canm bem identifiedm andm excluded.
2- m Lowm Variability:m Consistentm /similar/m closem resultsm ofm repetitions,
/clusteredmaroundmthem meanm →m SmallmSDm/m narrowmrangem/merrormbars.
3- mNonmoverlappingmerrormbars→mSIGNIFICANTmdifferencemormcorrelation.
4-mRepeatablembymothermscientists,mgivingmthemsame/similarmresults.
m
NB:m(repeatingmdoesmNOTmmakemyourmmeasurementsmmoremreliable,mitmjust
m helpsmyoumtomspotmandmremovemanomalies,massesmandmjudgemthemdegreemo
fmvariability,mhencemreliability!)
• Randomm error:m Unpredictablem ,m occasionalm errorm inm one*m orm morem ofm th
emmeasurements,musuallymcausedmby:
1-
m problemminmthemcontrolledmvariablesm,morm
2m-inaccurateminstrument.
-Ex.m whenm weighingm yourself,m andmstandingm differentlym onm them scale,
orm lookingm atm them levelm ofm am liquidm eachm timem fromm am differentm angle,m or
m difficultyminmstandardisingmthempressuremormforcemapplied.
-Correctedm bym :m Performingm manym repetitions,m excludem them anomalies.
2
