Descriptive statistics (MOCT/MOS) Flashcards
Define measures of central tendency.
A method to find out the average score from a data set using (mode, median, mean)
Define mean
Average value in a data set
How do you calculate mean?
Add scores up
Divide by the number of ppts
Mean- Strengths
most robust as it uses all the scores to provide an average
Mean Weakness
Can be skewed by exteme low/high scores (anomalies)
Shouldn’t be used when there are extreme scores
Why is the mean a useful calculation?
Data summary, comparisons, predictive value
Define mode
Most frequent value or category in a data set
Mode- Strengths
Not skewed by anomalies
Useful to show the most popular value
Mode- weakness
Less robust- Only uses the most frequent score- ignoring all other data
Can’t be used if theres more than 1 mode
why is the mode a useful calculation?
used for categorical data. Where data is divided into categories
How to work out mode?
Put scores in rank order
Identify the most frequent value
Why shouldn’t the mode be used when there is more than 1 mode?
There are more than 1 categories that occur within the same highest frequency. So the mode doesn’t provide a single unique value to describe the mode
Define median
The middle value of a data set. when arranged in acceding/descending order
Median- strengths
Not skewed by extreme high or low values (anomalies)
Median- weakness
less robust. Only uses middle scores ignoring data that is v high/low
Why is the median a useful calculation?
useful for data where the order matters, like when you’re ranking things
more reliable when you don’t have many numbers to work with.
How to work out median?
Put scores in rank order and identify middle value (divide by 2 if there are 2 medians)
Define measures of spread
Describes how spread out/varied the values in a data set are through calculations of range, and standard deviation.
(How much the individual values in a data set differ/vary from each other)
Define range
Refers to the difference between the higher and lowest values in a data set.
How is the range calculated?
- Finding the largest and smallest value in a data set.
- Subtracting the smallest from the largest
- Add 1
Why is there 1 added to the range?
To account for the fact that the scores are often rounded up and down in research. And make sure both highest/lowest values are included in the range.
Range- strengths
Quick, and easy to calculate
Range weakness
Less robust as it only uses highest and lowest scores. (Which could be skewed by anomalies) that aren’t typical of the majority of ppts.
Standard deviation definition
Shows the amount of variation/dispersion of individual data points from the mean of a dataset.
Groups with scores that are more spread out….
Have larger standard deviations
Groups with closely clustered scores have….
Smaller deviations
What does it mean if the standard deviation of 2 groups are similar?
Not much variation/ They have similar variations around the mean
Standard deviation- strength
More robust- uses all scores to show how far a group of scores vary from the mean
Not influenced by extreme scores at either end of the data set
Standard deviation- weakness
Time consuming to calculate
When are bar charts used?
Used for categorical, ordinal data, and frequency distributions
Describe how to plot the dv and iv on bar charts.
Levels of the iv= X axis
The dv=Y axis
When are histograms used?
To show the pattern of a whole data set and distribution of numbers/scores (how numbers are spread out eg height/age)
Describe how to plot scores on a histogram
The dv: is plotted on the x axis (categorises)
The frequency of each score: is plotted on the y axis
Scattergram definition
The results of a correlational study are displayed on a scatter gram.
Describe how to draw a scatter gram
- Plot points
- Draw a line
- Line of best fit
How does a strong correlation look like on a Scattergram?
Data points are close to the line
How does a weak correlation look like on a Scattergram?
Data points are more spread out
