Measures of central tendency and dispersion Flashcards
Define descriptive statistics.
The use of graphs, tables and summary statistics to identify trends and analyse sets of data.
What does it mean to measure central tendency?
The general term for any measure of the average value in a set of data.
How do you calculate the mean?
Add up all of the scores or values in a data set and divide them by the total number of scores that there are.
Strength of the mean?
Most sensitive of the measures of central tendency as it includes all of the scores/values in a data set. More representative of the data as a whole.
Limitation of the mean
Extreme values can easily distort the results so it does not represent the data overall.
What is the median?
The middle value in a data set.
How do you work out the median?
List the scores in the data set from lowest to highest and find the middle. In an odd number of scores, the median is easily identified whereas in an even number the median is halfway between the two middle scores.
Strength of the median
Extreme scores do not affect it. Easy to calculate.
Limitation of the median
Less sensitive than the mean and extreme values may be important. The actual values of lower and higher numbers are ignored.
What is the mode?
The most frequently occurring score/value within a data set.
What is it called if in a data set there are two modes?
bi-modal
How to find the mode?
Find the most common number in a data set.
Strength of using the mode.
Easy to calculate.
Limitation of using the mode.
When there are several modes in a data set, this information is not very useful.
Give some measures of central tendency.
Mean
Median
Mode
What does it mean to measure dispersion?
Measuring the spread or variation in a set of scores.
Give some examples of measures of dispersion.
Range
Standard Deviation
How do we calculate the range?
A simple calculation of the spread of scores by taking the lowest value from the highest value. Usually you would add one after.
Why would we add 1 after calculating the range?
Allows for the fact that raw scores are often rounded up (or down) when they are recorded. (Accounts for a margin of error).
Give a strength of using the range.
Easy to calculate.
Give a limitation of using the range.
Only takes into account the two extreme values and this may be not be representative of the whole data set.
Does not indicate whether most numbers are closely grouped around the mean or spread out- standard deviation does show this.
What is standard deviation?
A sophisticated measure of dispersion in a set of scores. It tells us by how much, on average, each score deviates from the mean.
What does a high standard deviation mean?
Not all participants are affected by the IV in the same way because data is widely spread.
What does a low standard deviation mean?
Data is tightly clustered around the mean which may imply that all participants responded in a fairly similar way.
Strength of standard deviation.
Much more precise measure of dispersion than the range as it includes all values in the final calculation.
Limitation of standard deviation.
Can be distorted by a single extreme value.
