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DATA COLLECTION AND SUMMARIZATION Observational Study Terms Population: the entire group of interest Sample: a part of the population selected to draw conclusions about the entire population Census: sample that attempts to include the entire population. Parameter: concept that describes the population (mean, median, std. dev, variance, etc) Statistic: a number produced from the sample that estimates a parameter Inferential statistics are used to make generalizations about the real world from sample data. Descriptive statistics describe data. Experiment Terms Experimental group: A collection of experimental units subjected to a difference in treatment, imposed by the experimenter Control group: A collection of experimental units subjected to the same conditions as those in experimental group except that no treatment is imposed. Quantitative Data Typical: characterized by the center of the data Spread: reported as an interval containing most of the data Symmetric: roughly the same mirror image on each side of the center value Skewed data: data has one side much longer than the other relative to the mode. Statistics for quantitative data Median: middle observation if the values are arranged in increasing order. Mean: average, given by: Inter-quartile range, IQR: Q3-Q1: the middle 50% of the data Sample variance, s 2 : Standard deviation, s: square root of sample variance. Preferred because it has the same units as the data. o Sample mean and st. deviation are good measures of center and spread for symmetric data If the data is skewed or has outliers, the sample median and IQR are more commonly used. Outliers affect the mean more than the median. Right skewed: mode<median<mean Left skewed: mean<median<mode Summary Statistics o P th percentile: the value such that p*100% of the values are below it and (1- p)*100% are above it. o
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This note was uploaded on 10/04/2010 for the course STAT STAT 211 taught by Professor Idontremember during the Spring '10 term at Texas A&M.

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