Statistics for the Terrified: Glossary
Click on an item below to see the definition
p value:
Hand-in-hand with the test statistic is the p value which indicates
the probability of getting the characteristics observed in a sample if the null hypothesis were true.
Paired t test:
A test on the change that occurs in
a measurement carried out on the same subject under two different conditions,
eg. before and after a therapeutic treatment.
Parameters:
Variables not in the data, but in the model (eg. distribution,
line of best fit) which describes it, eg. mean, gradient, standard deviation.
Parametric statistics:
That branch of statistics based on the estimation and testing of
parameters (usually normally distributed data).
See also Non-parametric statistics, Parameters.
Percentile:
A 10 percentile is the value (of a particular variable such as weight)
beneath which 10% of the population falls. A 50 percentile is the value beneath which 50% of the population
falls. These could also be written as 10%ile and 50%ile.
Placebo:
A non-active treatment applied as a control in a study where psychological
factors could affect the outcome. This allows the observation and quantification of any procedural effects involved
in the trial that have nothing to do with any administered treatment.
See also Placebo effect.
Placebo effect:
Improvement in outcome that is consistent but not due to any treatment or
non-treatment administered. This is only a factor for human beings and possibly animals where psychology of care
can affect outcome.
See also Placebo.
Population:
The set of all possible subjects from which a sample can be drawn.
Population distribution:
The distribution of the population from which a sample was drawn.
See also Distribution.
Power:
The ability to reject the null hypothesis when it is false.
Probability:
The likelihood of an event happening;
must be between 0 and 1.
Proportion:
An observed fraction of the total.
Prospective study:
By nature a long-term experiment, which plots the progression from
an initial state to the particular state under examination. For example, how many first-time prisoners from a
particular prison re-offend within one year of release?
See also Retrospective study.
Protocol:
The protocol of an experiment is a set of rules laid down at the start
to impose a rigid structure on everyone involved, to ensure consistency, and to provide a focus for the
experiment by defining of the decision rule.
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