Statistics Flashcards
Statistics, population, sample
Statistics: collecting, analyzing, interpreting data
Population: a large group of people/animals/objects to be tested
Sample: subset/subgroup of population (the group we’re testing)
Random and representative sample
Random sample: sample obtained in a way that every member of population has an equal chance to be selected
Representative sample: exactly what it sounds like
Frequency, data item, frequency distribution
frequency: how often something occurs
Data item: piece of data
Frequency distribution: table of how many times each thing occurred
Grouped frequency distribution/classes
Class width
Grouping data points when we have a bunch that are hard to read
Class width: number from subtracting two consecutive class limits (smaller from bigger)
How to calculate mean?
Mean = sum of items/number of items
How to calculate mean for frequency distribution?
Mean = sum [(data value X frequency)]/ # data items
AKA
sum(xf)/n
How to calculate median when even # of data items?
Mean of two middle data items
How to find position of median?
(n+1)/2 where n = number of data items
How to find mode?
Most frequent data value
How to find midrange?
(Lowest value + highest value)/2
How is correlation coefficient measured? How does it relate to graphs?
-1 to 1 (strongest negative to strongest positive)
The more scrunkly the graph around LOBF, the weaker the correlation
How do significance levels work?
Decimal to percent, 0.05 = 5% means 5% chance of no correlation in population
What is regression line? Simple equation?
Line of best fit = good old y=mx+b
How to calculate range?
Highest value - lowest value
How to calculate standard deviation? (6 steps)
Find mean
Find deviation of each item
Square each deviation
Sum them ^
Divide sum by n-1
Take that square root ^
What is normal distribution? What is the rule?
Data clusters around mean, spreads or narrows w standard deviation
Rule: 68-95-99.7 = percent of data within 1-2-3 standard deviations respectively
What is a Z-score? How do we calc?
How many standard deviation an item is from mean.
Z-score = (data item - mean)/SD
