Descriptive Statistics Flashcards
What are the measures of central tendency?
Mean
Median
Mode
What is the mean?
Arithmetic average
Add up and divide by n
What are the strengths of the mean?
Most sensitive
Takes all scores into account
What are the weaknesses of the mean?
Affected by extreme values (outliers) which can skew data
What is the median?
Middle value in an ordered list
What are the strengths of the median?
Not affected by extreme values
What are the weaknesses of the median?
Not as sensitive as the mean
Difficult to calculate with a large data set
What is the mode?
Most frequently occurring value in a data set
What are the strengths of the mode?
Useful for nominal data
Simplest to calculate
What are the weaknesses of the mode?
Not useful when there are many modes
What are the measures of dispersion?
Range
Standard deviation
What is the range?
Subtract lowest from highest number
What are the strengths of the range?
Convenient
Easy to calculate
What are the weaknesses of the range?
Affected by extreme values (outliers)
Doesn’t reflect distribution
What is standard deviation?
Mean distance of values from the mean
What are the strengths of standard deviation?
Most precise, uses all the values
What are the weaknesses of standard deviation?
May hide extreme values
Not immediately sensed
What does a high and low standard deviation show?
High SD - the spread is wide
Low SD - scores are clustered
What are bar charts?
Show the relative size of the data collected
Bars shouldn’t touch because the data isn’t continuous
What are frequency tables?
Focus on groups of scores
e.g. how often each event occurred
Frequency is calculated by totalling the number of tallies for each group
What are histograms?
Groups of numbers into ranges
Used to represent the data in a frequency table
Bars should be touching because the data is continuous
Frequency axis must start at 0
What are scatter diagrams?
Represents the strength and direction of a relationship between co-variables in a correlational analysis
Correlational data, dot for x and y values
Positive correlation, scatter from bottom left to top right
Negative correlation, scatter from top left to bottom right
What is normal distribution?
Normal distribution is a bell-shaped symmetrical frequency curve showing a mean, median and mode which all fall at the mid-point
What is skewed distribution?
Skewed distribution occurs when the mean, median and mode are not similar, and if scores are bi-modal (or multi-modal)
Negative skew - the scores in a distribution are bunched towards the right. The mode is to the right of the mean because the mean is dragged to the left by extreme scores tailing in a negative direction (tail to the left)
Positive skew - the scores in a distribution are bunched towards the left. The mode is to the left of them mean because the mean is dragged to the right by extreme scores tailing a positive direction (tail to the right)
