What is an Independent variable?
This is the variable you change to see what effect it has. This is the cause.
What is a control variable?
This will affect the outcome of an investigation as well as the independent variable. These should be kept the same to make a fair test. If impossible to keep constant they should at least be monitored to judge their affect on the outcome.
What is a dependent variable?
This is what you measure as a result of the changes in the independent variable. And the effect.
What is a continuous variable?
A variable that can have any numeric value. Length/ temperature etc. Line graphs are appropriate.
What is a categoric variable?
These have values that are described by labels/names. E.g. the effect of different metals on acids. The type of metal is a categoric variable. You must use pie charts or bar charts.
What is a discrete variable?
A categoric variable that has values restricted to whole numbers. E.g. the number of carbon atoms in a chain.
What is an ordered variable?
A categoric variable that can be ranked. E.g. lumps of rock that can be large, medium or small.
Define - Accuracy
This is a measurement that is close to the true value.
Define - Calibration
This is where you fix known points and then mark a scale on an instrument between those fixed points. E.g. thermometers, the fixed points are the melting and boiling points of water. The scale between is 0 to 100.
Define - Data/datum
A collection of measurements. (Datum is the singular of data).
Define - Random error
These cause readings to be different from the true value. Caused by human error/faulty technique/faulty equipment. Can be detected and compensated for by taking a large number of readings.
Define - Systematic error
Cause readings to be spread about some value other than the true value. All the readings are shifted one way or other from the true value. E.g. a thermometer that always reads 5˚c higher than it should.
Define - Zero error
A type of systematic error. Caused by a measuring instrument that has a false zero. A balance that shows a reading when nothing is on it.
Define - Evidence
Data which has been subjected to some form of validation. We can decide how important data is when coming to a judgment.
Define - Fair test
Happens when only the independent variable has been allowed to affect the dependent variable. Achieved by keeping all other variables constant.
Define - Precision
Determined by the limits of the scale of the instrument being used. It is related to the smallest scale division of a measuring instrument. E.g. a ruler marked in mm is more precise than a ruler marked in cm. 10.1cm (101mm) is more precise than 10 cm.
Define - Reliability
Results are considered reliable if they can be repeated. If someone else can do the experiment and get the same results then they are more likely to be reliable. Reliability can be improved by carrying out repeats and calculating a mean.
Define - True Value
The accurate value which would be found if the measurement could be made without any errors at all.
Define - Validity
Data is only valid for coming to a conclusion if the measurements are affected by a single independent variable only. If you investigated the affect of size of particles on a reaction and the temp changed, then the temp would affect your results and the data would no longer be valid. Not a fair test.
Define - Sensitivity
How quickly an instrument reacts before you take a measurement and/or a measure of the precision of an instrument.
Define - Range
The top and bottom value of a series of measurements. E.g. collect data over the range 0 to 200˚c.
Define - Intervals
The difference between each measurement within a range. E.g. at intervals of 10˚c.