Graphs

When asked about information in tables, what should you always include?

Always quote the numbers shown in the table.

What is a bar chart used for?

Used for data in discrete categories (categorical data).

What does discrete data mean?

Numerical data that can only take certain, fixed values, often whole numbers, and is obtained by counting.

What is a scattergram used for?

Used for correlational data to show the relationship or association between two variables.

What does a scattergram show?

Direction and strength of a correlation between two variables.

What is a histogram used for?

Used for continuous data rather than discrete data.

What type of data do histograms display?

Interval or ratio (continuous) data.

What is a line graph used for?

Used for continuous data to show how something changes in value over time.

What does a line graph show?

Trends or patterns over a continuous scale.

What is a normal distribution?

A symmetrical, bell-shaped curve where most scores cluster around the mean.

What are the key features of a normal distribution?

Mean, median and mode are all equal and located at the centre.

In a normal distribution, where are most people’s scores found?

Around the middle of the curve, tapering off at both ends.

What is a skewed distribution?

A distribution where the data are not symmetrical.

What causes a skewed distribution?

Extreme values pulling the mean towards one side.

What is a positive skew?

Most scores are low; the tail is on the right. Order: mode, median, mean.

What is a negative skew?

Most scores are high; the tail is on the left. Order: mean, median, mode.

How do you identify a positive skew from a graph?

Tail extends to the right; mean is greater than the median.

How do you identify a negative skew from a graph?

Tail extends to the left; mean is less than the median.

What measure of central tendency is most affected by skew?

The mean.

What kind of data produces a bell-shaped curve?

Continuous data with an even distribution around the mean.

What does the peak of a normal distribution represent?

The most frequent or average score.