Everything Flashcards
Weighted mean vs arithmetic mean! + formulas
The weighted mean is considered if some occasions are more important than others. While the arithmetic mean has his importancy equally disturbed on the values (Xn/n), WM hasn´t.
Weighted mean = Σwx/Σw
Σ = the sum of (in other words…add them up!).
w = the weights.
x = the value.
Sometimes it can happen that the sum of your weights it more than one, that can happen.
What is a Factorial?
”!”, which indicates to multiply every number before and including the given number. So:
4!= 1234
!4= 4321
How to detect bad statistics?
- self-selection study: someone stands to gain financially from the results of a trial or survey (like company paied the trial)
- Voluntary response samples: are not suitable for
statistics, because they carry a heavy bias toward people who have strong opinions (often negatives ones). (when prof asks you to look into his book) - Correlation isnt Causation(mind other factors)
- Journal Bias: Journals report more trials that went positive(p.e. drug is efficient instead of not efficient. P-value …)
- Misleading percentages: Unemployment may have “slowed by 50%,” but if the unemployment rate was previously 100,000 new unemployment claims per month, that still means 50,000 people are joining the unemployed ranks every month.
HOW TO TELL THE DIFFERENCE BETWEEN DISCRETE AND CONTINUOUS VARIABLES?
If a variable takes you forever to count (like temperature, because 3.3, 4,3222…) than it is a continous variable. If you can count it, it is a discrete variable.
HOW TO TELL THE DIFFERENCE BETWEEN A STATISTIC AND A PARAMETER?
A statistic is based on a sample and was calculated upward on scale. You do that when your group is too big. P.e. 40% of all germans like the law. It is not possible to ask so many germans, thus it was a sample calculated upwards.
A Paramter includes everthing. You ask a class og 5th grader if they like football. 70% raise their hand. So 70% of THAT 5th graders in the population like football.
HOW TO TELL THE DIFFERENCE BETWEEN QUANTITATIVE AND QUALITATIVE VARIABLES?
Quantitative means it can be counted, like “number of people per square mile.” Qualitative means it is a description, like “brown dog fur.”
What looks a right/left skewed distribution like?
Like a normal distribution but with the top of the bell more to the left(then:right skewed) or right(vice versa).
HOW TO FIND THE SAMPLE VARIANCE AND STANDARD DEVIATION?
Variance: Sum(x-xmean)**2
____________
n-1
The SD is just the squareroot of that.
The variance also describes how spread out the data is.
What can we do with a COEFFICIENT OF VARIATION and how to find it?
We can compare two tests and how people made them, even if the tests have different scales, measurment systems. We compare the results of SD / MEAN *100% for the tests
What to do if I have 4 dishes, 6 meals, 3 beverages and 6 desert to choose, and I want to know how many possible combinations there are.
4x6x3x6
HOW TO FIND THE PROBABILITY OF SELECTING People FROM A GROUP? We have 8 footballers (included 3 females) and 6 basketballers (included 4 females). What is the probability of randomly choosing a female or footballer.
(8/14)+(7/14)-(3/8)
Add the probabilities of the 2 options and subtract the Schnittmenge (footbaler AND female)
85% of employees have health insurance; out
of this group, 45% had deductibles higher than $1000. How many people had deductibles higher than $1,000?
.85 × .45 = .3825
How to find out if 2 events are mutually exclusive?
events exclude themselves mutually, if:
P(A|B)=P(A)+P(B)
if they are the same, thus both numbers are equal, they exclude mutually.
What is a sample space?
A sample space is the set of all possible probabilities.
