RESEARCH METHODS- descriptive statistics Flashcards
What are the measures of central tendency?
Mean, median and mode.
What is standard deviation?
The standard deviation (σ) is a measure of how much numbers in a data set deviate from the mean (average). It is calculated as follows:
Example data set: 59, 79, 43, 42, 81, 100, 38, 54, 92, 62
Calculate the mean (65)
Subtract the mean from each number in the set
-6, 14, -22, -23, 16, 35, -27, -11, 27, -3
Square these numbers
36, 196, 484, 529, 256, 1225, 729, 121, 729, 9
Add all these numbers together
36+196+484+529+256+1225+729+121+729+9=4314
Divide the result by the number of numbers
4314/10=431.4
The square root of this number is the standard deviation
√431.4=20.77
The standard deviation is 20.77
How do you work out percentage change?
To calculate a percentage change, work out the difference between the original number and the after number, divide that difference by the original number, then multiply the result by 100:
Example: He got 80 marks on the test but after studying he got 88 marks on the test
88-80=8
8/80=0.1
0.1*100=10
His test score increased by 10% after studying
What is a normal distribution?
A data set that has a normal distribution will have the majority of scores on or near the mean average. A normal distribution is also symmetrical.
What is a skewed distribution?
A data set that has a skewed distribution will not be symmetrical: Scores are not distributed evenly either side of the mean.
Skewed distributions are caused by outliers: Freak scores that throw off the mean.
What are positive and negative skewed distributions?
Positively skewed: A freakishly high score (or a cluster of low scores) makes the mean much higher than most of the scores, so most scores are below the mean.
Mean > Median > Mode
Negatively skewed: A freakishly low score (or a cluster of high scores) makes the mean much lower than most of the scores, so most scores are above the mean.
Mean < Median < Mode
What is a correlation?
Correlation refers to how closely related two (or more) things are related. For example, hot weather and ice cream sales may be positively correlated: When hot weather goes up, so do ice cream sales.
