Aqa Biology As "how Science Works" Glossary

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Accuracy

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this type of measurement is one which is close to the true value.

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Anomalous data

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"........" data are those measurements that fall outside the normal, or expected, range of measured values. Variation is a characteristic of all living organisms, and it is often difficult in biological investigations to distinguish between data that reflect this variation and those that are genuinely "........". A large number of readings allows "........" data to be identified with greater certainty.

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Calibration

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When using a measuring instrument, this process involves fixing known points and constructing a scale between these fixed points.

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Causal link/Relationship

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A change in one variable that results from or is caused by a change in another variable.

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Confounding variable

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A "..........." variable is one that may, in addition to the independent variable, affect the outcome of the investigation. "............" variables must be kept constant or the investigation will not be a fair test. In some investigations, ecological investigations in particular, it is not always possible to keep "..........." variables constant. In such cases, these variables should be monitored. In this way it may be possible to decide whether or not the factor concerned affects the outcome of the experiment. "........" variables are sometimes referred to as control variables.

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Control Experiment

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This is set up to eliminate certain possibilities. In a well designed investigation, the independent variable is changed and all confounding variables are kept constant. The possibility exists, however, that something else other than the independent variable might have produced the results that were obtained.This type of experiment is one that is designed to eliminate this possibility.

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Control group

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A group that is treated in exactly the same way as the experimental group except for the factor that is being investigated. This allows scientists to make a comparison. It ensures that the data that are collected are valid because any differences between the results for the experimental group and those for the "this" group will be due to a single independent variable.

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Control variable

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See confounding variable

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Correlation

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...shows that there is a relationship between two variables, however, it might not be a causal one.

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Dependent variable

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the variable the value of which is measured for each change in the independent variable.

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Double-blind trial

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A trial, usually used in the context of medicine, when assessing the effects of a new drug or treatment on humans. Neither the patients nor the scientists concerned know which treatment a particular individual is receiving until after completion of the trial. This helps to avoid bias and increase the validity of the trial.

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Errors

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these cause readings to be different from the true value.

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Evidence

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The data or observations that are used to support a given

hypothesis or belief.

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Independent Variable

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the variable for which values are changed variable by the investigator.

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Placebo

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a dummy pill or injection given to members of a control group in medical trials. Where this is in the form of a pill, it should be identical to the pill used with the experimental group. The only difference should be that that it does not contain the drug being trialled. The use of this helps to ensure that the data collected from a trial are valid.

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Precision

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is related to the smallest scale division on the measuring instrument that is being used. A set of ......... measurements will have very little spread about the mean value.

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Probability

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"........' is the likelihood of an event occurring. It differs from chance in that it can be expressed mathematically. In statistical tests, "........" are usually expressed as a decimal fraction of one. Thus a "........" of 0.05 means that an event is likely to occur 5 times in every 100.

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Random distribution

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"......." distribution is one that arises as a result of chance. When investigating, for example, variation in living organisms, the data collected will only be valid if they have been collected at random. This avoids observer bias and allows statistical tests to be used in an analysis of the results of the investigation.

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Chance

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essentially the same as luck. If a coin is tossed in the air, whether it comes down heads or tails is purely due to "this". The results of any investigation could have a genuine scientific explanation but they could be due to "this". Scientists carry out statistical tests to assess the probability of the results of an investigation being due to "this".

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Random errors

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these errors occur in an unpredictable way. They may be caused by human error, faulty technique in taking measurements or by faulty equipment.

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Raw data

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instrument readings and other data collected at the time of the investigation. These data may subsequently be processed and used to calculate percentages and standard deviations.

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Reliability

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The results of an investigation may be considered to be '.....' if they can be repeated. If other scientists get the same results, then the results of the initial investigation are more likely to be '.....'. The '.....' of data within a single investigation can be improved by carrying out repeat measurements.

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Systematic errors

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These errors cause readings to be spread about some value other than the true value. In other words, all the readings are shifted in one direction from the true value. 'These' errors may occur when using a wrongly calibrated instrument.

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Validity

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Data are only '.....' if the measurements that have been made are affected by a single independent variable only and all variables other than the IV are kept constant. They are not '.....' if the investigation is flawed and confounding variables have been allowed to change or there is observer bias. Conclusions are only '.....' if they are supported by '.....' and reliable data measured to an appropriate level of accuracy.

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Zero errors

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These errors are caused by instruments that have an incorrect zero. A .... error may occur when the needle on a colorimeter fails to return to zero or when a top-pan balance shows a reading when nothing is placed on the pan.

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Fair test

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only the independent variable has been allowed to affect the dependent variable. A ".... ....." can usually be achieved by keeping all other variables constant or controlled.