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Statistics
a set of mathematical procedures for organizing, summarizing and interpreting information

Population
the entire set of the individuals of interest for a particular research question

Sample
a set of individuals selected from a population, usually intended to represent the population in a research study

Variable
a characteristic or condition that changes or has different values for different individuals

Data (plural)
measurements or observations

Data set
a collection of measurements or observations

Datum (singular)
a single measurement or observation, commonly called a score/raw score

Parameter
a value, usually a numerical value, that describes a population. Usually derived from measurements of the individuals in the population

Statistic
a value, usually a numerical value, that describes a sample. Usually derived from measurements of the individuals in the sample

Descriptive statistics
statistical procedures used to summarize, organize and simplify data

Inferential statistics
techniques that allow us to study samples and then make generalization about the populations from which they were selected

Sampling error
the naturally occurring discrepancy, or error, that exists between a sample statistic and the corresponding population parameter

Correlational method
two different variables are observed to determine whether there is a relationship between them
aka correlational research strategy

Experimental method
one variable is manipulated while another variable is observed and measured. To establish a causeandeffect relationship between the two variables, an experiment attempts to control all other variables to prevent them from influencing the results

Confounded
whenever a research study allows more than one explanation for the results because it is impossible to reach an unambiguous conclusion

Random assignment
each participant has an equal chance of being assigned to each of the treatment conditions

Independent variable
the variable that is manipulated by the researcher. It usually consists of two (or more) treatment conditions to which subjects are exposed. It consists of antecedent conditions that are manipulated prior to observing the dependent variable

Dependent variable
the variable that is observed to assess the effect of the treatment

Control condition
when individuals do not receive the experimental treatment. Instead, they either receive a neutral, placebo treatment. It provides a baseline for comparison with the experimental condition.

Control group
individuals in the control condition

Experimental condition
individuals who do receive the experimental treatment. Often called the experimental group.

Quasiindependent variable
in a nonexperimental study, the "independent" variable that is used to create the different groups of scores

Constructs
aka hypothetical constructs
internal attributes or characteristics that cannot be directly observed but are useful for describing and explaining behavior

Operational definition
identifies a measurement procedure (a set of operations) for measuring an external behavior and uses the resulting measurements as a definition and a measurement of an internal construct.
It has two components:
1. it describes a set of operations for measuring a construct
2. it defines the construct in terms of the resulting measurements

Discrete variable
consists of separate, indivisible categories. No values can exist between two neighboring categories

Continuous variable
there are an infinite number of possible values that fall between any two observed values. It is divisible into an infinite number of fractional parts

Real limits
boundaries of intervals for scores that are represented on a continuous number line.
The real limit separating two adjacent scores is located exactly halfway between the scores.
Each score has two real limits

Upper real limit
This is at the top of the interval

Lower real limit
This is at the bottom of the interval

Nominal scale
it consists of a set of categories that have different names.
Measurements on this label and categorize observations, but do not make any quantitative distinctions between observations

Ordinal scale
it consists of a set of categories that are organized in an ordered sequence.
Measurements on an ordinal scale rank observations in terms of size or magnitude

Interval scale
it consists of ordered categories that are all intervals of exactly the same size.
Equal differences between numbers on the scale reflect equal differences in magnitude.
However, the zero point on this scale is arbitrary and does not indicate a zero amount of the variable being measured

Ratio scale
an interval scale with the additional feature of an absolute zero point.
With this scale, ratios of numbers do reflect ratios of magnitude

Sigma
the Greek letter used to stand for summation
the sum of a set of scores

