Sampling
Experimental know how
Reliable results are experiments
that give the same data.
To ensure that:
• each time the experiment is
repeated
• each time the experiment is
reproduced by other scientists
Step 1:
Divide the
field into a
grid
Valid results are both reliable and
comes from the experiment being a fair
test.
To improve validity you could: Only
change one variable and measure how it
affects another variable.
There are three variables:
The independent variable, the dependent
variable and the control variable.
To improve reliability you need to repeat your measurements and calculate
the mean. You need to repeat each measurement at least three times.
How to make an experiment safer:
Hazards include:
•
Microorganisms for
e.g bacteria that
makes you ill
•
Chemicals for e.g
flammable ethanol
and corrosive acids
•
Fire
•
Electricity which
makes you prone to
shocks
Precision
Sampling
How to reduce these
hazardsIf you are working
with hydrochloric acid
wear gloves and
goggles.
If you’re using a
busen burner,
prepare a heat proof
mat.
Et
h
i
c
s
Step 2: Label the
grid along the
bottom and up
the side with
numbers
Step 3: Use a
random number
generator to
select
coordinates ie.
(2,6)
Take your
samples at
these
coordinates
All organisms involved in your investigations needed to be treated safely and ethically.
Animals need to be treated humanely and handled carefully, any animals captured
from the wild should be returned to their original habitat.
Animals kept in the lab should be cared for and not be kept in overcrowded conditions
for e.g.
if your experiment involves students, make sure they should not be forced to take part
against their will or feel pressure to take part.
How to improve the accuracy of
an experiment?
The accuracy
depends on the
method you are using,
for example if you are
measuring gas
bubbles instead of
estimating the
number of bubbles,
you could measure
the volume of gas.
To take population samples you use quadrats or transects, if
you only take one part of the area, your results will be biased.
To prevent bias:
For
example if
you are
measuring
the length
of a potatio
chip, start
from 0mm
Precision means all the data is really close to the mean and not
spread out.
Sampling data helps draw conclusions about the whole population so
it is important that it is representative. To ensure this, sampling should
be random.
You should be
able to indentify
an anomalous
result and
calculate the
mean.
How to plan an experiment1. Say what you are measuring
2. Say what you are changing
3. Describe the method and apparatus
4. Describe control variables
5. Say whether you are using a control or not
C
O
R
M
S
GRAPHS ➡️
How can an experiment be improved?
1. Comment on the method (was it valid, is there control variables)
2. Comment on the quality of results (were the results valid, reliable and precise?)
3. Were there anamolous results, if there were why did they occur and what variables could
have affected the results?
4. How confident you are that the results are correct
5. Changes to the method that could improve the quality of results
6. Make predictions