Introduction to Statistics - Lecture Notes | PSYC 215, Study notes of Psychology

Download Introduction to Statistics - Lecture Notes | PSYC 215 and more Study notes Psychology in PDF only on Docsity! Introduction to Statistics 1. Overview of Course and Requirements 2. Research Methods Overview a. Correlational/Observational method: Make observations of two variables as they exist naturally to observe if there is a relationship. Cannot establish cause-and-effect in the relationship b. Experimental Method: One variable is manipulated while changes are observed in another variable. 3. Terminology a. Variable: A characteristic or condition that changes or has different values for different individuals. i. Independent variable: The variable that is manipulated by the researcher. The “cause” ii. Dependent variable: The variable that is observed for changes in order to assess the effect of the treatment. The “effect” b. Data: Measurements collected in research; often they are scores, but may be ranks, categories, types, etc. c. Statistics: A set of methods and rules for organizing, summarizing, and interpreting information. i. Descriptive: Statistical procedures used to summarize, organize and simplify data. (i.e., averages, tables, graphs) Examples include: Scores from first exam for 88 students, Public attitudes towards death penalty, Rates of adolescent drug and alcohol use ii. Inferential: Consists of techniques that allow us to study samples and then make generalizations about the populations from which they were selected. Examples include: Scores from first exam for 88 students to infer mean of all students in all classes, A sample of public attitudes towards death penalty to infer the attitude of the population, Rates of adolescent drug and alcohol use to infer substance use for the population of adolescents in the U.S. d. Population: Set of all individuals of interest in a particular study. e. Sample: A set of individuals selected from a population, usually intended to represent the population in a study. 4. Different ways of describing variables a. Discrete or Continuous i. Discrete: Possible values are limited (e.g., number of children in a household). ii. Continuous: Possible values are theoretically infinite, given sufficiently precise measurement (e.g., height, temperature, IQ) b. Qualitative vs. Quantitative i. Qualitative – values designate membership in distinct groups (e.g., religions, male/female, married/never married/divorced) ii. Quantitative – numerical values indicate the amount of something and arithmetic operations are sensible. c. Scales of Measurement i. Nominal: A categorical variable where the categories have no ordered values. Value denotes group membership, but no information about quantity e.g., gender (1=male, 2=female); race -- religion -- experimental condition ii. Ordinal: A categorical variable where the categories are ordered. Value denotes rank ordering, but distance between values not necessarily equal e.g., order of finish in a race, 1=very happy; 2=satisfied; 3=very unhappy iii. Interval: A set of categories that are in an organized sequence with equal intervals between the values on the measurement scale; no absolute zero point Temperature in Fahrenheit, SAT scores iv. Ratio: An interval scale with an absolute zero point. Most physical measurements (weight, height, speed), Number of correct answers on a test 5. Summation a. Use the Greek Letter Sigma: ∑ b. Order of operations 1. Brackets/parentheses first ( ) 2. squaring, exponents x2, Öx 3. multiplication, division ´, ¸ 4. addition/summation, subtraction +, S, - 6. Today’s Sticking Points a. There is not a clear consensus on how to define the independent variable i. Some people believe that it requires a manipulation in order to technically be called an IV ii. Some people just like to think of it as the “cause” (and thus refer to correlational studies as having an IV) b. It is not always clear in which scale of measurement a variable may fall in. i. Height measured in inches or as short, medium, tall? c. There is no clear consensus on what Likert-type questions or scales (e.g. on a scale of 1-7) are considered. i. Ordinal or interval? The scores may be collected as a whole value, but they are generally treated as continuous. ii. For our purposes, we will treat them as they are conventionally: interval