psychstats

• Statistics


  Branch of mathematics that focuses on the organization, analysis and interpretation of group of numbers
• Descriptive statistics


  Used to summarize and describe a group of numbers from research study
• Inferential statistics


  Used to draw conclusion and to make inference that are based on the numbers from research study but that go beyond the numbers
• Population


  The entire set of individuals of interest for particular research question
• Sample


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


  Characteristics that can have different values
• Construct


  Internal characteristic that cannot be directly observed
• Values


  Possible number or category that variable can have
• Score (datum)


  Particular person's value on a variable
• Data/data set


  Collection of measurement or observation, complete set of scores
• Parameter


  Value, usually a numerical value, that describe the population
• Statistic


  Value, usually a numerical value that describe the sample
• Sampling error


  The naturally occurring discrepancy that exist between a sample statistic and the corresponding population parameter
• Levels of measurement


  • Nominal
  • Ordinal
  • Interval
  • Ratio
• Discrete variable


  Has specific values and cannot have values between the specific values
• Continuous variable


  There are in theory an infinite number of values between any two values
• True dichotomous


  Naturally formed two categories
• Artificial dichotomous


  Reflects an underlying continuous scale forced into a dichotomy
• Frequency distribution


  An organized tabulation of the number of individuals located in each category on the scale of measurement. Can be structured either as table or graph
• Frequency table


  Ordered listing of number of individuals, subjects, respondents having each different values for a particular variable
• Proportion


  Measure the fraction of the total group that associated with each score
• Percentage


  An amount of something often expressed as a number out of 100
• Interval


  Range of values in grouped frequency table that are grouped together
• Central tendency


  Statistical measure that attempts to determine the single value, usually located in the center of distribution that is most typical or most representative of the entire set of scores
• Mean


  Also known as arithmetic average, sum of all scores in the distribution divided by the number of scores
• Weighted mean


  An average in which each observation in the data set is assigned or multiplied by a weight before summing to a single average value
• Median


  The middle score when all of the scores in the distribution are arranged from the lowest to highest
• Mode


  The score or category that has the greatest frequency
• Kurtosis


  Extent to which a frequency distribution deviates from the normal curve in terms of whether its curved in the middle is more peaked or flat than the normal curve
• Types of kurtosis


  • Leptokurtic
  • Mesokurtic
  • Platykurtic
• Variability


  Provides a quantitative measure of the difference between the scores in a distribution
• Range


  The distance covered by the scores in a distribution from the lowest to highest score
• Variance


  The average of each score's squared difference from the mean
• Standard deviation


  Uses the mean of the distribution as a reference point and measures variability by considering the distance between each score and the mean
• Formulas for standard deviation

  • Computational formula
  • Definitional formula
• Biased statistics


  Consistently overestimates or underestimates the corresponding population parameter
• Median absolute deviation


  A robust measure of how spread the data is if the assumptions of standard deviation were not met
• 1. score


  The number of standard deviations that a score is above or below (if negative) the mean of its distribution
• Raw score


  An ordinary score as opposed to a z-score
• Normal curve


  Mathematically defined, bell-shaped frequency distribution that is symmetrical and unimodal (also called Gaussian distribution)