Psychology Statistics Chapter 1

Statistics

A set of mathematical procedures for organizing, summarizing, and interpreting
information

Population (N)

the set of all the possible individuals in a particular study

Sample (n)

set of individuals selected from the 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. In statistics, they are usually identified by the letters X and Y

Data (Plural)

measurements or observations of a variable

Data set

a collection of measurements or observations

Score (Raw Score)

a single measurement or observation

Parameter

a numerical value that describes the population

Sample statistic

a numerical value that describes the sample

Descriptive statistics

procedures used to summarize, organize, and simplify data

Inferential Statistics

techniques that allow us to make generalizations about the populations from which the data was collected

sampling error

the amount of error that exists between a sample statistic and the
corresponding population parameter

Constructs

internal attributes or characteristics that cannot be directly observed (e.g.,
intelligence)

Operational definition

identifies the set of operations for measuring a behavior. Uses the resulting measurements as both a definition and a measurement of a construct

procedure for measuring external behavior wherein the resulting measurements measure a hypothetical construct

Categorial/Discrete variables

Cannot be divided infinitely. No values can exist between two neighboring categories. Numbers may be used the categories as a “label/code”

ex: 1 for men, 2 for women, 3 for non-binary

Continious Variables

Infinitely divisible variables, numbers on a number line

ie: height in inches, iron in blood in ml, hours slept in a day

Binary Scales

• Classifies a variable into categories/groups with ONLY two possibilities
• No numerical or quantitative properties

example: alive/dead, pregnancy

Nominal Scales

• Classifies a variable into categories/groups with more than two
possibilities
• Set of categories that have different names, cannot be ranked

ie: eye color, political orientaion, gender, year

Ordinal Scale

• Allows variable levels to be rank ordered
• There are no values attached to the intervals, so you cannot determine the magnitude of the differences between them

Set of categories that are organized in an ordered sequence

Interval Scale

• Difference between the numbers is meaningful and can be ranked
• Intervals are equal in size
• Quantitative value, but no meaningful zero reference point

Set of rank ordered categories that are all intervals of exactly the same size

Ratio Scale

Quantitative with all numerical properties including an absolute zero reference point

set of order, equal categories wherein a zero score indicates none of the variable being measured, allowing meaningful ratio

Correlational method

observing two different variables to determine whether there is a relationship between them within a single group of people

The experimental method

manipulating one variable (IV) while another variable (DV) is observed and measured

Control group

individuals do not receive the experimental treatment → they either receive no treatment or a placebo treatment. The purpose of this
is to provide baseline data for comparison with the experimental group

Experimental group

individuals receive the experimental treatment (a
drug, a therapy, a method of teaching, etc)

Confounding variable

variables not controlled in an experiment that might provide
more than one explanation for the results

Non experimental method

still compares two groups of scores on a dependent
variable, but one variable is unable to be manipulated or randomly assigned (quasi-independent variable)

∑

a specialized symbol used to stand for summation

∑X

a statistical notation meaning “the sum of scores” → requiring you to sum all the X values

Real limits

Boundaries of intervals for scores that are represented on a continious number line. This seperates two adjacent scores is located halfway between 2 scores (ie: 7.5-8-8.5)