Topic 3 Flashcards
What is descriptive statistics?
Collection of methods for CLASSIFYING and SUMMARISING data
What are the two main types of descriptive statistics?
- Measures of central tendency
2. Measures of validity
What are frequency distributions?
A count of the number of occurrences of each different value in the data set
How do you make a frequency distribution?
- Count the number of occurrences (frequency) of each DV value
- Plot the graph
X axis -> values of DV
Y axis -> frequency
What kind of value range is a frequency distribution good for?
A narrow value range
What kind of value range is a Class interval good for?
Used for wide value ranges
Describe a Class Interval scale
- The width of the interval is the number of values the in the interval
- Should choose widths like 10-20 intervals
- Choose odd number interval width
Why should a class interval have an odd numbered interval?
Allows the midpoint to be a whole number
What is a midpoint?
The point halfway through the interval
What limits are best to use for continuous variables?
Exact limits
Describe exact limits
1/2 unit below and 1/2 unit above the class interval
How would you calculate the midpoint when using exact limits?
Lower exact limit + 1/2 class interval width
What are the axes for a frequency polygon and histograms?
X axis = mark axis with values corresponding to Class Interval midpoint
Y axis = frequency
In a histogram would you put space between the bars for continuous data?
No
Describe uniform/rectangular distribution shape
Evenly distributed throughout
Describe skewed distribution shape
Lots of scores at one end and relatively few at other end
Can be positive or negative
Of which end of the distribution would positively skewed data be?
Left
Of which end of the distribution would negatively skewed data be?
Right
Describe normal distribution
- Symmetric distribution
- Many scores in the middle, progressively fewer at either end
