EMPA Flashcards
Accuracy
An accurate measurement is one which is close to the true value.
Anomalous data
Measurements that fall outside the normal, or expected range of measured values.
A large number of readings allows anomalous data to be identified with greater certainty.
Calibration
When using a measuring instrument, calibration involves fixing known points and constructing a scale between these fixed points.
Casual Link
Change in one variable that results from or is caused by a change in another variable.
Chance
Essentially the same as luck. The results of an investigation could have a genuine scientific explanation but they could be due to chance.
Scientists carry out statistical tests to assess the probability of the results of an investigation being due to chance.
Confounding variable
One that may, in addition to the independent variable, affect the outcome of the investigation.
Confounding variables must be kept constant or the investigation will not be a fair test.
Sometimes referred to as control variables.
Control Experiment
An experiment that is set up to eliminate certain possibilities.
used to eliminate possibility that something other than the independent variable might have produced the results obtained.
Control Group
A group treated exactly the same way as the experimental group except for the factor that is being investigated. Allows comparison.
Ensures that data is valid because any differences between the results for the experimental group and those for the control group will be due to a single independent variable.
Correlation
Shows that there is a relationship between two variables, however, it might not be a casual one.
Dependent variable
The variable the value of which is measured for each change in the independent variable.
Double-blind trial
A trial, usually in context of medicine, when assessing the effects of a new drug on humans. Neither the patients nor the scientists concerned know which treatment a particular individual is receiving until after completion of the trial.
Helps avoid bias and increase validity of the trial.
Errors
Errors cause readings to be different from the true value.
Evidence
The data or observations that are used to support a given hypothesis or belief.
Fair Test
A fair test is one in which only the independent variable has been allowed to affect the dependent variable. A fair test can usually be achieved by keeping all other variables constant or controlled.
Hypothesis
Sometimes known as an experimental hypothesis, this is the possible explanation of a problem that can be tested experimentally.
Independent Variable
The variable for which values are changed by the investigator.
Null hypothesis
A statistical test requires a clear hypothesis to test. Often difficult to predict what would happen as the result of the investigation.
It is much easier to phrase a hypothesis in terms of there being no difference or no association. A hypothesis worded in this way is a null hypothesis.
As the result of carrying out a statistical test, a decision can be made about whether to accept or reject null hypothesis.
Placebo
Dummy pill/ injection given to members of a control group in medical trials. Where a placebo is in the form of a pill, it should be identical to the pill used with the experimental group.
Use of placebos helps to ensure that the data collected from a trial are valid.
Precision
Precision is related to the smallest scale division on the measuring instrument that is being used. A set of precise measurements will have very little spread about the mean value.
Probability
The likelihood of an event occurring. Differs from chance in that it can be expressed mathematically.
Protocol
Once an experimental method has been shown to produce valid and reliable results, it becomes a protocol used by other scientists.
Random Distribution
A distribution that arises as a result of chance. When investigating, e.g. variation in living organisms, the data collected will only be valid if they have been collected at random. Avoids observer bias.
Random Errors.
Occur in an unpredictable way. This may be caused by human error, faulty technique or faulty equipment.
Raw Data
Instrument readings and other data collected at time of investigation. These data may subsequently be processed and used to calculate percentages and standard deviations.
Reliability
The result of an investigation considered reliable if they can be repeated.
Within an investigation, reliability of data increased by repeats.
Systematic errors
These errors cause readings to be spread about some value other than true value. All readings are shifted in one direction from the true value. May occur when using a wrongly calibrated instrument. `
True Value
This is the accurate value which would be found if the quantity could be measured without errors.
validity.
Data are only valid if the measurements that have been made are affected by a single independent variable only.
NOT valid if investigation flawed and control variables have been allowed to change or there is observer bias.
Conclusions only valid if they are supported by valid and reliable date measured to an appropriate level of accuracy.
Zero errors
Caused by instruments that have an incorrect zero.
