What is used to help me understand the data?
- Stem and leaf plots
- box plots
- Histograms
- Looking for skewness
- Comparing data sets visually
What is used to help others understand data?
- Bar Graphs
- Scatterplots
What do histograms do?
Good at showing the distribution of the data.
What do stem and leap plots do?
And how do they work?
Show distribution of the data
Easy to do, Stem makes up the tens and the leafs make up the units
Why are boxplots useful?
-useful for showing medians, ranges, IQ range, skewness etc.
Describe the structure of a box plot?
Upper adjacent value is the line at the top
Lower adjacent value is the line at the bottom(difference between two provides range)
The top and bottom line are known as upper and lower hinge( Interquartile range is difference between the two)
Line in the middle is the median
- Outliers are displayed as dots further away from adjacent values
- extreme outliers are displayed as stars
What do whiskers on a box plot indicate about data?
The more similar in length the more likely that the data is normally distributed vice versa
What is a frequency distribution?
- Histograms
- made of touching bars
- each bar is the frequency that the given value occurs
- We can count how many people have a healthy heart rate
What is a probability distribution?
- Bell curves
- Smoothed over to flow nicely
- Area under curve is the probability that the value occurs
- We can work out the likelihood of a person producing a certain outcome with a normal distribution.
Why is it ideal to have normally distributed data?
-It allows us to do better an more accurate statistical tests.
What are two ways in which a distribution can deviate away from normality?
- Lack of symmetry (skewness)
- Pointyness (Kurtosis)
What is skewness?
Deviation from symmetry
It also means some extreme scores are affecting the mean
What is kurtosis?
Refers to the extent to which scores cluster at the ends (tails) of the distribution which tends to change how pointy they look.
What is a distribution with positive kurtosis known as ?
Leptokurtic distribution
-more pointy
What is a distribution with negative kurtosis known as?
Platykurtic
-Tends to be flatter than normal
Why is distribution important ?
-Tells us which measure of central tendency and dispersion represents our sample best
-
If our data is normally distributed what measure of central tendency and dispersion should we use?
MCT= mean
MD =SD
If our data is skewed what MCD and MD should we use?
MCT=median
MD=Range
How does skewness statistics on SPSS indicate the distribution of data?
Perfectly normally distributed data has a skewness of 0
More than twice the standard error data is likely to be skewed
Why is distribution important?
- Tells us which measure of central tendency/dispersion represents our sample best.
- also tells us which inferential statistics to use
If we have a normal distribution which measure of central tendency and dispersion should we use?
-mean and SD
If we have skewed distribtuion which measure of central tendency and dispersion should we use?
-median and range.
Why are figures and tables helpful in letting others understand data?
They can be used to assess and illustrate data quickly and easily.
How are tables supposed to be formatted according to the APA?
Only used for descriptive statistics
Labelled and titled
Placed at the top of the most appropriate page
Font and size should be the same as the main text
Logical and easy to understand
