Page 380 - Statistics for Dummies

364
Statistics For Dummies, 2nd Edition
misleading statistics (continued)
sources, checking, 39
tornado statistics, 36–37
observational studies
uncovering, 35–41
defi ned, 262
wording of questions as factor in, 40–41
overview, 263
missed detection, 226
Old Faithful’s eruptions, boxplots for,
missing data as factor in errors, 41
120–121
mistake recognition
omission errors, 34
anecdotes, avoiding influence of, 330

on your own, trying problems, 334
biased data, sources of, 323–324
ordering takeout, pie charts for, 94–95
confounding variables, revealing, 327–328
ordinal data, 47
correlations, detecting misinterpreted,
organizing data in surveys, 259
326–327
original sources, 33

data fishing, avoiding, 329–330
outliers
graphs, avoiding misleading, 319–323
boxplots, 121–122
incorrect numbers, looking for, 328–329
described, 52, 293
margin of error, checking for, 324
histograms, 109
random samples, checking for, 325 • O •
overstated results, 21, 275–276
sample size, checking, 325–326
motorcycle fatalities, statistics about, 25
movies, statistics about, 30 • P •
• N • paired t-tests, 61, 236–240
parameters
described, 50, 193, 194
negative t-values, 231–232 statistics linked to, 194–195
90th percentile (top 10%), 155 percentiles
no treatment in experiments, 267 ACT scores, comparing, 87–89
non-random sample, 49–50 calculating, 84–85
normal approximation, 155–156 described, 84
normal distribution high, 153–154
examples of, 144 household incomes, comparing, 86–87

finding probabilities for, 149–151 interpreting, 85–89
mean, 143 kth percentile, 84–85
overview, 54–55, 143–146 low, 152–153
percentiles for, fi nding, 152–155 90th percentile (top 10%), 155
properties, 144–145 overview, 53
standard deviation, 143 10th percentile (bottom 10%), 155
Z-distribution (standard normal t-table, 160–161
distribution), 146–149 percentiles for normal distribution
null hypothesis, 61, 216–217 fi nding, 152–155
numerical data. See also graphing high percentiles, 153–154
numerical data low percentiles, 152–153
described, 71, 103 steps for fi nding, 152
summaries for, 15
wording in percentile problems,
translating, 154–155
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