Click on an item below to see the definition
Data:
Information (usually numeric) collected on the participants in a study and
on which data analysis is performed.
Data types:
All data is not the same, and different types of data must be
handled in different ways.
See also Binary data,
Categorical data, Continuous data, Count, Discrete data, Ordinal data.
Decision rule:
A clear statement made at the outset of a study detailing how a
decidion on significance is to be made.
Degrees of freedom:
This crops up everywhere in statistical tests, and is used to calculate the
p value. It is a fairly deep mathematical topic and we need not go fully into it here. Broadly speaking, the
larger the sample size, the larger the df: the smaller the sample, the smaller the df. However, this is
modified by the number of groups you have and the parameters being estimated. A small df makes it more
difficult to detect significance.
Dependent variable:
The term used for the outcome variable in regression analysis. A
variable that depends on another variable is called the dependent variable: the variable on which it depends
is called the predictor variable (sometimes the independent variable).
See also Linefitting.
Descriptive statistics:
Simple summary description of data carried out before a full analysis, eg.
Mean, Standard error, etc.
Discrete data:
Data that can only take a small set of particular values, usually
whole numbers. For instance, you cannot actually have 2.4 children.
See also Data types.
Distribution:
A graph plotting probability against values. There are some typical shapes:
normal, uniform, exponential. The normal distribution (bell-shaped) is the most common.
See also Normal distribution,
population distribution, null distribution.
Double blind:
When neither subject nor evaluator knows what treatment or regime has been
administered. This double-blind approach reduces the risk of bias (psychological or
otherwise) being introduced by either the investigator or the subjects of the study.
Single-blind occurs when one of these two is aware of the treatment or regime
administered. See also Bias, Blinded evaluation, Blind study, Single blind.
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