1A: key science skills

Experimental design skills - hypothesis, independent variable, dependent variable, controlled variables, control group, accuracy, precision, systematic errors, random errors, repeatability, reproducibility

hypothesis

• educated prediction / testable statement

  • how your Iv will affect the DV

  • include direction of change

structure of hypothesis

If (IV / experimental group), then (prediction including change in DV) … because … (link to biological concept)

independent variable

variable / factor that you manipulate / change on purpose

dependent variable

variable / factor that you measure

• changed when independent variable is manipulated

controlled variable

factors other than IV that are kept constant

• prevents influence on the DV

control group

• baseline to compare the experimental group with

• ensures results are caused by IV

accuracy

• how close a measurement is to the true value

  • true value: value / range of values that would be found is the quantity could be measured perfectly

precision

• two or more measurements that are close to each other in value

  • affected by random errors

outlier

• readings that lie a long way from other results

• repeating the experiment can help identification

systematic error

• causes readings to differ from the true value by a consistent amount each time a measurement is made

• affects accuracy

examples of systematic errors

• clock is 5 mins slow

• leaking gas cylinder

• observer bias

preventing systematic errors

• calibrate equipment, use high-quality tools

• include known reference standards to check

• use triggered electronic timers

random errors

• unpredictable variations in measuring that result in a spread / range of readings

• affect precision

examples of random errors

• reaction time with stopwatch

• parallax error if viewed from different angles

• controlling size of drop of fluid from pipette

• estimating a quantity between two lines

reducing random errors:

• cannot eradicate competely

  • taking repeated measurements and using a larger sample size

  • controlling extraneous variables

  • using equipment with higher sensitivity

  • improve experimental techniques

repeatability

ability to achieve closeness of results (precision) when experiment is repeated under the same conditions

reproducibility

closeness of results carried out under changed conditions of measurement

improvements of experimental design

• increasing sample size

• implement proper controls

• randomisation

• controlling extraneous variables

qualitative data

• non-numerical

• descriptive

quantitative data

• numerical

• measurable

validity

• only the independent variable should be influencing the dependent variable

• valid experiment = no bias + control group

extraneous

• uncontrolled variable

• introduces error, variability

• any variable other than the IV which varies between the experiment and controlled