Flashcards · 7357 · Topic 13

L: Data presentation and interpretation flashcards

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Frequency density: Frequency ÷ class width. The height of a histogram bar.
Relative frequency: Frequency ÷ total frequency. Estimates a probability.
Interquartile range (IQR): Q₃ − Q₁. The spread of the middle half of the data.
Regression line y = a + bx: what does b mean?: The estimated change in y when x increases by 1, in context, with units.
Regression line y = a + bx: what does a mean?: The estimated y when x = 0. Often meaningless if x = 0 is far outside the data.
Cleaning data: missing values: Leave out, say so, reduce n. Never record them as 0.
Cleaning data: outliers: Investigate. Remove only if they are errors or not from the population.
Two rules for identifying outliers: Below Q₁ − 1.5 × IQR or above Q₃ + 1.5 × IQR. Outside x̄ ± 2σ (or x̄ ± 3σ if the question says so).
Mean and standard deviation of raw data: x̄ = Σx/n σ = √(Σx²/n − x̄²)
Cumulative frequency graph: where are points plotted, and where are the median and quartiles read?: Plot at upper class boundaries. Read the median at n/2 and the quartiles at n/4 and 3n/4.
Interpolation vs extrapolation with a regression line: Interpolation predicts inside the range of the observed x-values (more reliable). Extrapolation predicts outside it (unreliable).