Psych Stats

• In a typical bell curve, 50% falls above average and 50% falls below average
• Easter Egg: An actuary is someone who analyzes the financial risks
• There are 2 types of statistics: descriptive statistics and inferential statistics
• Descriptive stats: Things you can count; means, medians, modes, ranges
• Inferential stats: requires actual math (e.g. differences between each group )
• Operational definitions are the specific criteria that are used to define the concepts and variables in a study.
• By definition, data needs to represent something, it is not just math
• Statistics: set of mathematical procedures for collecting, organizing, and interpreting data.
• Population is the group of people you want to study
• Sample: a set of individuals from a population, usually intended to represent the population in a research study
• Variable: a characteristic or condition that changes/has different values for different individuals
• A statistic describes a sample while a parameter describes a population
• discrepancy is the amount of error that exists between a sample statistic and the population parameter
• correlational method: a method of studying two variables by measuring the relationship between them
• correlation does not equal causation
• experimental methods compare between groups of scores, have independent and dependent variables, and determine a cause and effect relationship
• the outcome measure in an experiment is the dependent variable
• a type of independent variable is the control measure
• you need at least 2 levels of independent variables
• you need at least one dependent variable
• nonequivalent groups- comparing groups that are not equal
• quasi-independent variables: variables that are not directly manipulated by the researcher but are still included in the study
• discrete variable: a variable consisting of separate indivisible categories, measured in whole numbers
• continuous variable: a variable that can take on any value (infinite) between two or more values. (e.g weight, height)
• sigma: add it up!
• frequency distribution: organize tabulation of the amount of people in each category
• N: number of values in a data set
• proportion: the fraction of a total group that have the same score.
• grouped frequency distribution is used when there is too much data to list
• positive skew (right skew)

  data shifted to the left end
• negative skew (left skew)

  data shifted to the right end
• symmetrical (no skew)

  average bell curve
• p= f/N
• each interval is called "class intervals"
• highest value-lowest value= range
• percentile rank 


  % of people who scored at or below a certain value
• cumulative frequency 


  accumulation of scores as you move up the scale
• 3 characteristics of distribution

  shape, central tendency, and variability