1.1.3 Evaluating Experimental Methods

Question 1

How do you evaluate experimental methods?

Answer 1

Evaluating experimental methods is an important skill for a scientist
A good way to evaluate an experimental design is by repeating the experiment yourself (using the instructions provided) and determining if you can produce similar results
When analysing and criticising the design of an experiment there are several key things to consider
Method limitations
Accuracy
Precision
Reliability
Validity

Question 2

What is method limitation?

Answer 2

A method limitation is any experimental design flaw or fault in the method that affects the accuracy of the results
It is crucial that any limitations within an experiment are identified and removed/corrected
For example, in an experiment using a potometer to measure the rate of water uptake in plants, there could be an air bubble inside the plant xylem
The bubble in the apparatus is a limitation as it prevents the accurate measurement of water uptake
It can be corrected by ensuring that all plant stems are cut underwater to prevent the entry of air

Question 3

What is accuracy?

Answer 3

Accuracy is how close a reading/measurement is to its true value
Accuracy can be reduced by the presence of errors in an experiment
Faulty instruments or flaws in the experimental method produce systematic errors that are repeated consistently every time the instrument is used or the method is followed
Unexpected environmental changes or incorrect use of equipment can produce random errors that are different every time the experiment is carried out, e.g. a breeze blowing during a potometer experiment may not blow at the same speed throughout the experiment

Question 4

What is precision?

Answer 4

Precision - how similar repeat readings/measurements are to each other
Readings that are tightly clustered together (a small range) are described as precise
The precision of a measurement is reflected in the values recorded – measurements to a greater number of decimal places are said to be more precise than those to a whole number

Question 5

What is reliability?

Answer 5

Experiments are repeated many times to ensure the reliability of results

Question 6

What is validity?

Answer 6

The other variables in the experiment are identified and controlled in order to ensure the validity of an experiment
Ideally the design of an experiment should be evaluated at the preliminary stage, this way any corrections or adjustments can be made prior to conducting the actual experimen