Psych Statistics Chapter 1, 2 and 4

• A population is a collection of all possible members of a defined group
• A sample is a subset of observations drawn from the population of interest
• A parameter describes population
• A statistic describes the sample
• A variable is any characteristics that take on different values
• Discrete Observations is data measured in whole units or categories
• Continuous Observation is measured in a continuum, can take on a full range of values including decimals
• Types of Variables:

  • Nominal: categories, discrete, colors, shapes
  • Ordinal: rankings or sequence, discrete, birth order
  • Interval: equally speed observations, either, temperature, calendar year, (Arbitrary 0 Point)
  • Ratio: interval variables that have meaningful 0 points, either, speed
• Interval and Ratio variables are called scale variables, where they are treated the same way
• An Independent Variable (Predictor) is manipulated to determine effect on dependent variable in experiment
• The Dependent Variable or Outcome Variable is measured which causes changes in the independent variable
• The confounding variable is anything that systematically varies with IV and might have an impact on DV
• Correlational Studies are an association of two or more variables and they cannot demonstrate cause and effect
• Random Assignments: distributes confounding variables and reducing it for individual differences in the study
• Between-Group Design: people are exposed to one level of IV
• Within-Group Design: all participants are exposed to both levels of IV
• Frequency is how often values in a data set occur
• Distribution is how a variable is spread throughout data
• n = number of people
• A histogram is a graph that depicts frequencies for one scale variable
• An outlier is the extreme score that is either lower or higher compared to the rest of the scores in a sample
• A Skew is a shape of data with abnormalities
• Normal Distribution: a frequency distribution that is a bell-shaped, symmetric unimodal curve
• Skewed Distribution: a frequency distribution in which one of the tails is pulled away from the center
• A Positive Skew is where the tail points to the right and a Negative Skew is where the tail points to the left
• Control Tendency is the descriptive statistic that best represents the center of a data set
• The mean is the arithmetic average group of scores
• The median is the middle score in a sample when all scores are arranged in order
• The mode is the most frequently occurring number in a sample
• Unimodal Distribution is when there is one mode
• Bimodal Distribution is when there are two modes
• Multimodal Distribution is when there are more than two modes
• Modes can be used in 3 Ways:

  1. One particular score dominates a distribution
  2. Multimodal or Bimodal Distribution
  3. Data is nominal
• Variability tells you about the spread in a distribution
• The range is the measure of lowest to highest score
• The Interquartile Range (IQR) is the measure of distance between first and third quartile
• Variance is the average of the squared deviations from the mean
• Standard Deviation is the typical amount each score differs from the mean