02 Descriptive Statistics Free Online FlashCards

What is a frequency distribution?

A frequency distribution lists possible values or intervals and the number of observations in each.

How is relative frequency calculated?

Relative frequency is the proportion or percentage of observations: $\text{frequency} \div \text{total observations}$.

How do bar graphs and histograms differ?

A bar graph displays categorical data with separated bars; a histogram displays quantitative intervals with touching bars.

What is the arithmetic mean?

The mean is the sum of all observations divided by their number: $\bar{x}=\frac{\sum_{i=1}^{n}x_i}{n}$.

How is the range calculated?

The range is the maximum value minus the minimum value: $\text{Range}=\text{maximum}-\text{minimum}$.

What does the 80th percentile indicate?

The 80th percentile is a value below which approximately 80% of observations lie and at or above which approximately 20% lie.

What does a z-score represent?

A z-score expresses an observation's distance from the mean in standard-deviation units: $z=\frac{x-\mu}{\sigma}$ for a population.

How does the 1.5-IQR rule flag outliers?

The 1.5-IQR rule defines fences as $Q_1-1.5(\text{IQR})$ and $Q_3+1.5(\text{IQR})$; values outside them are potential outliers.

What should you do when an outlier appears?

A possible outlier should be investigated: check the record and units, assess population membership, compare conclusions with and without it, and report treatment transparently.

Which summaries suit skewed data?

Use mean and standard deviation for roughly symmetric data; use median and IQR when data are skewed or contain extreme values.

Which graph shows association between two quantitative variables?

A scatterplot displays the association between two quantitative variables measured as paired values.

How is the median determined?

The median is the middle ordered value; with an even number of observations, it is the mean of the two middle values.