Statistics

by Christen and Sue

 

Statistics Basics

  • Statistics- numerical facts assembled in such a manner that they provide that such a manner that they provide significant information about measures or scores.
  • Sample- part of a population
  • Population- a complete group from which a sample is selected.
  • Range- a measure of variability; they distance between extreme measure or scores
  • Average- central tendency of a group of measures, expressed in means, median and mode.

Descriptive Statistics

  • Descriptive Statistics- the branch of statistics that is concerned with providing information about a distribution of scores.

    • The Frequency Distribution

    • Frequency Distribution- an ordered set of data that indicates how frequently scores appear.
    • Histogram- a graphic representation of a frequency distribution that uses rectangular solids. 
    • Polygon- a closed figure.

    Measures of Central Tendency

    • Mean - a type of average calculated by dividing the sum of scores by the number of scores.
    • Median - the scores beneath which 50% of the cases fall.
    • Mode - the most frequently occurring number or score in a distribution.
    • Bimodal- having two modes.

    Measures of Variability

    • Range- the difference between the highest and the lowest scores in a distribution.
    • Standard Deviation- a measure of the variability of a distribution, attained by the formula
    • S.D.  =  Sum of d^2/N ALL THIS IS UNDER A SQUARE ROOT
    • d =  the deviation of each score from the mean of the distribution
    • N = the number of scores in the distribution

    The Normal Curve

    • Normal Distribution: a symmetrical distribution in which approximately 68% of cases lie within a standard deviation of the mean.
    • Normal Curve- graphic presentation of a normal distribution, showing a bell shape.

    Correlation Coefficient 

    • Used to show that there is/isn't a relationship between 2 things
    • +1.00 to -1.00
    • +1 = perfect positive correlation; 
    • -1 = prefect negative correlation, 
    • 0.00 = no correlation 
    • DOESN'T IMPLY CAUSE & EFFECT

    Scatter Diagram

    • Graphic representation of the relationship between 2 variables
    • Reliability : in psychological measure, consistency.
    • Test-retest: reliability- consistency of a test a determined by a comparison of scores on repeated testings.
    • Valid: the degree to which a test measure what is it supposed to measure.

Inferential Statistics

  • Infer- to draw a conclusion.
  • Inferential Stats: branch of stats concerned with the confidence with which conclusions drawn about samples may be tested to the populations from which they were drawn.

    • Statistically Significant Differences

    • Psychologists use formulas involving means & standard deviations of sample groups to determine whether group differences are statistically important.

    Samples and Populations

    • Psychologists use mathematical tools that they apply to samples of scores to determine whether they can generalize their finds to populations of scores. 
    • Samples must accurately represent the population it is supposed to represent.