Descriptive statistics Flashcards
What are descriptive statistics?
a way of describing quantitative data and identifying any patterns or trends.
What are the two methods for descriptive statistics?
Measures of central tendency
Measures of dispersion
What are the levels of measurements?
nominal
ordinal
interval
What is nominal data?
data that is presented in named groups or categories. For example, ice cream flavours or film genres.
What is ordinal data?
data that is presented in rank order, but the distance between points on the scale is unknown eg. most to least, but the gap between each score would be different,
What is interval data?
data that can measured in fixed units with equal distance between points on the scale. For example, temperature measured in centigrade, or weight measured in kilograms.
What are measures of central tendency?
This informs us about central (or middle) values of a set of data. They are averages – ways of calculating a typical value for a set of data.
hese can be calculated in different ways, each one appropriate for a different situation - mean, median and mode.
When is the mean used?
Used for interval data.
Strength of using the mean?
Most sensitive measure of central tendency because it takes account of the exact distance between all of the values of all the data.
Limitation of using the mean?
Due to sensitivity – can be distorted by extreme values therefore becoming unrepresentative of the data set
When to use the median?
Interval and ordinal data
Strength of using the median?
Not affected by extreme scores, can be easier to calculate than the mean and can be used for ordinal data
Limitation of using the median?
Not as sensitive, the exact values are not reflected…just the middle numbers.
When to use the mode?
nominal, ordinal and interval
Strength of using the mode?
Unaffected by extreme values and is the only measure which can be used for nominal data.
Limitation of using the mode?
It is not useful for explaining data when there is more than one mode
What is the measures of dispersion?
This refers to how dispersed or spread out data items are.
How to find out the measures of dispersion - range?
find the lowest value and highest value, minus the lowest value from the highest value then +1.
Strength of measures of dispersion - range?
Easy to calculate
Limitation of measures of dispersion - range?
Is affected by extreme values
Fails to take into account the distribution of values, therefore does not give a fair representation of the general spread of data
How to find out the measures of dispersion - standard deviation?
a measure of the average distance between each data item above and below the mean.
Strength of measures of dispersion - standard deviation?
much more sophisticated measure of dispersion because it takes into account all the exact values in a data set.
Limitation of measures of dispersion - standard deviation?
Like the mean, SD can be distorted by extreme values.
Data distributions?
When data is displayed on a graph, we often see a bell curve – the way this bell curve looks helps us to find out how the data is distributed.
We use the average and then the standard deviations to work out how the data is distributed.
Normal distibution?
This is a classic bell shaped curve and shows the data is equally distributed. The distribution is symmetrical around the middle point
Skewed distibutions?
Negatively skewed (left skewed) – the mean is lower than the mode and median.
Positively skewed (right skewed) - the mean is higher than the mode and median.
