# BIOL 2060 Lecture Notes - Mosaic Plot, Contingency Table, Scatter Plot

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Displaying Data

2.1 Displaying frequency Distributions

- Relative Frequency: proportion of observations having a given measurement

(freq. /total number of observations)

- Relative freq. Distribution: shows the proportion of the occurrences of each value

in the data set

- Frequency table: text, showing the # of occur. In each category

- Bar graph : height of rectangular bars to visualize the frequency of each category

- You can organize the table by putting the most frequent at the top

- Rules for bar graph: baseline must be zero, and you must label the graph.

- Bars should be of the same width and start at the baseline and shouldn’t be fused

together, provide total number of observations in the figure legend.

- Histogram: uses area of rectangular bars to display frequency, splits into bins,

equal width, uses RANGES

- Mode (histogram): highest peak ..bimodal means 2 peaks

- Symmetric: two sides are mirror images

- Skewed: if not symmetric ...skewed right: tail on the right...skewed left: tail on

the left

- Outliers: extreme data points, removed if SHOWN to be errors

- To choose the width of ranges (histogram): look at if what the data shows on 2

separate graphs is true or not

- Rule (histogram): bars rise from baseline zero, no separation between bars, at the

boundary then place in the higher interval..sturges rule of thumb: 1+1(n)/ln2 (n is

the number of observations), but we use more intervals than sturges, break at

god numbers

2.2 Quantiles of a frequency distribution

- Percentile: value below which x% of the individuals lie...also X/100 quantile

- Cumulative frequency distribution: graph of all the quantiles of a numerical

variable

2.3 Associations between categorical variables

- Contingency table: frequency table for 2 or more categorical variables (all

combinations)