Descriptive Statistics, Introduction to Probability Flashcards
Descriptive Statistics?
- numbers used to describe the data collected
- 5-10% of statistics
Statistic?
- descriptive measure from a SAMPLE
Mean of a sample (statistic) and the number of observations in the sample variable?
mean= x-bar (bar over top of x) # of observations in a sample= n
Parameter?
-descriptive measure computed from a population
Mean and # of observations in population in a parameter (population) variable?
mean= u # of observations in a population= N
Measures of Central Tendency?
3 measures of it?
- convey info regarding the average, midpoint and most common value collected in a. data set
- mean, median and mode
Measures of Dispersion?
- measure of the amount of spread/ how far apart the different data pieces are spread apart
- displays the measure of variability in a data set
Mean?
-Sum/ average
Subscript of “x” for finding the mean
- subscript just lists the different pieces of data
3 properties of mean?
- unique (can only be one)
- simplicity (easy to find)
- affected by extreme values
Median?
median with an even numbered set?
- median divides the data set into two equal parts
- to find it, list the data pieces in numeric order
- find which two pieces of data are in the middle, add them and then divide by 2
(n+1)/2th is the equation for finding the?
- median
- points to a location in a data set where you will find the median value
Mode?
- value in a data set that occurs most frequently
3 properties of the median?
- uniqueness
- simplicity
- NOT affected by outliers/ extreme values
Is there dispersion if all the value sin a data set are the same?
No
Range?
- difference b/w the highest value and lowest value in a data set
- effected by extreme values
- doesn’t use all the data pieces in a data set
Q1? Q2? Q3? (what are their percentiles?)
Q1= 25% of participants fall bellow this value (75 above) Q2= 50% of participants fall bellow this value Q3= 75% of values fall below this value (25 above)
Interquartile Range (IQR)?
IQR= Q3-Q1
-difference between the first and third quartiles that make up the middle 50% of the data
Data Skewness?
- data can be classified whether it is symmetric or asymmetric
- if symmetric, the left half and right half of a histogram frequency polygon are mirror images
+ or - if a graph is skewed to the left? right?
skewed left= negative
skewed right= positive
Negatively Skewed value)median v?
- median value is to the left of the peak of the graph
mean, median then mode [at the peak]
Positively Skewed (median value)?
- median value is to the right of the peak
- Mode[peak], median then the mean
In a symmetric distribution, where does the mean, median and mode lie?
- centre, around the peak of the graph
Variance?
- amount of spread around the mean value
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