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43 Cards in this Set
- Front
- Back
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individuals |
objects described by a set of data |
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variable |
any characteristic of an individual |
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categorical variable |
places an individual into one of several groups or categories (pie and bar) |
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quantitative variable |
takes a numerical value (histogram and stem plot) |
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unit of measurement |
seconds or kilograms |
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distribution (of a variable) |
what values it takes and how often |
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distribution of a categorical variable |
lists categories and gives either the count or the percent in each category |
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time plot |
plots each observation against the time that it was measured |
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what best plots quantitative variables? |
histograms and stemplots |
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what kind of variable is age? |
quantitative |
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Q1 and Q3 |
medians on each side of the median |
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five number summary |
minimum, Q1, M, Q3, maximum |
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boxplot |
central box spans Q1-Q3 line in box is M lines extend from box to min and max |
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IQR |
= Q3-Q1 |
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identifying outliers |
1.5 x IQR |
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resistant measures |
median and quartiles |
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non-resistant measures |
mean, correlation and SD |
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N(mean, SD) |
mean and SD of a normal distribution (0,1) |
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z= |
x-mean/SD |
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standardized value |
Z |
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response variable |
measures an outcome of a study (altered by the explanatory variable) |
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explanatory variable |
explain or influence change in a response variable |
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scatterplot |
displays the relationship between two quantitative variables measured on the same individual |
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correlation (r) |
measures the direction and strength of the linear association (positive and negative associations) |
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regression line |
straight line that describes how a response variable changes as an explanatory variable changes |
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least-squares regression line |
the line that minimizes the sum of the squares of the vertical distances of the observed points to the lines |
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influential observations |
individual points that substantially change the correlation or regression line |
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ecological correlation |
the tendency for correlations based on averages to be stronger than correlations based on individuals |
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extrapolation |
use of a regression line to predict values far outside the range of what was actually observed |
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lurking variable |
may explain the relationship between the explanatory and response variable |
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conditional distribution |
distributions of a row variable for each fixed value of the column variable, and vis versa (each value in the column as a percent of the column total) |
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bar graphs |
flexible means of presenting categorical data |
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sample survey |
selects a sample from the population of all individuals about which we desire information |
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random sampling |
uses chance to select a sample |
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stratified random sampling |
classify the population into strata, and then choose SRS from each stratum |
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bias |
systematic error in the way the sample represents the population |
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voluntary response samples are particularly prone to
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bias |
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forms of bias |
-undercoverage -nonresponse -response bias -poorly worded questions |
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experiments |
actively impose treatment (vs observational studies) |
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confounded variable |
effects on a response cannot be distinguished |
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randomization |
uses chance to assign subjects to the treatments |
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blocks |
individuals who are similar in some way |
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matched pairs |
subject receives both treatments, or subjects are paired as similarly as possible to compare treatments |
