[ Statistics ]: A collection of procedures and principles for gathering data and analyzing information in order to help people make decisions when faced with uncertainty. . [ Variable ]: a characteristic which changes when from observation to observation in a population. [ Categorical (Qualitative) Variable ]: A variable whose values cannot be interpreted as numbers. With categorical data, we can replace numbers with letters, symbols, etc. Note: When analyzing categorical data, we will typically work with counts or percentages of objects. [ Numerical (Quantitative) Variable ]: Measurements or counts, values which have meanings as numbers. Discrete : If the set of all possible values, when pictured on the number line, consists only of isolated points. The most common type of discrete variable we will encounter is a counting variable . Continuous : If the set of all values, when pictured on the number line, consists of intervals. [ Census ]: Look at every object or individual in the population. We know everything exactly, but it takes a lot of time and money, may even be impossible to do if measurements are destructive (e.g., average lightbulb lifetime). [ Sampling Variability ]: The differences between samples from the same population [ Random Sample ]: A subset of the population selected so that every individual has a specified probability of being part of the sample. [ Simple Random Sample ]: A random subset of size n from a population where the subset is chosen in such a way that every possible subset of size n has the same chance of being selected as any other. [ Sample Survey ]: A method of gathering opinions and information from each individual included in the sample. Possible problems: nonresponse bias and volunteer sample , both cause a nonrepresentative sample [ Case-Control Study ]: A study in which ‘cases’ having a particular condition are compared to ‘controls’ who do not. The idea is to compare them to see how they differ on the variable of interest. [ Experiment
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