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Statistics pieces of information presented in numerical form; this includes pictures (e.g. graphs, figures) too Population the entire set of all possible occurrences; can be broad or narrow Sample a subset of a population; often a subset selected for study - ideally, it closely resembles the population Accurate sampling sample statistics are similar to the population parameter Inaccurate sampling due to sampling error 2 broad categories of statistics Descriptive and inferential Descriptive statistics Organize and summarize information Inferential statistics Make generalized statements about a population; test hypotheses - experiments rely on these The scientific method A systematic way of gathering and interpreting observations 2 categories of observations Variables (can change); constants (do not change) Sampling How participants are selected - ideally random sampling is used Random assignment Placing participants into groups - experimental group and control group 2 types of variables Independent and dependent Independent variables manipulations; the treatment Dependent variables measurements; the data Qualitative variables e.g. names; usually non-numerical Quantitative variables e.g. exam scores; have numerical values Discrete variables Change in finite steps; often described with integers (e.g. number of students) Continuous variables Fall on an infinitely fine-grained scale; can be described with real numbers (e.g. reaction time) Types of experiments "True"; quasi-experimental; correlational "True" experiments Random sampling and assignment; manipulation of variables Quasi-experimental experiments Random selections but NO random assignment Correlational methods No experimental manipulation; investigate the relationships between variables 4 data scale types Nominal; ordinal; interval; ratio Nominal scale Described by name or type only; frequency-of-occurrence; no information about order or magnitude - Categorical Ordinal scale Can put data into orders or ranks; relative placement (no information about magnitude); e.g. order in which people finish a problem-solving task Interval scale Convey information about differences between numerical observation; relative magnitude (equal size intervals assumed); no information about absolute magnitude; e.g. thermometer Ratio scale Absolute zero point; can be described with ratios; convey information about absolute magnitude; e.g. all physical measures