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Statistics

QuestionAnswer
Define population The whole set of items that are of interest
Define sample Some subset of the population intended to represent the population
Define sampling unit Each individual thing in the population that can be sampled
Define sampling frame Often sampling units of a population are individually named or numbered to for a list
Define census Data collected from the entire population
Define simple random sample -Each sample has an equal chance of selection -Each item has number -Random number generator
Advantages of simple random sample -No bias -Easy -Cheap -Equal selection chance
Disadvantages of simple random sample -Not suitable for large population -Sampling frame needed
Define systematic sample -Elements ordered into list -Every kth element -k=pop size/samp size -Start at random number between 1 and k
Advantages of systematic sample -Simple -Quick -Suitable for large populations
Disadvantages of systematic sample -Sampling frame needed -Can introduce bias is sampling frame is not random
Define stratified sample -Population divided into strata -Simple random sample for each group -Samp size/pop size sampled from each group -Used when sample is large and divided into groups
Advantages of stratified sample -Reflects population structure -Proportional representation within population
Disadvantages of stratified sample -Population clearly classified into strata -Selection within strata suffer from same disadvantages as simple random
Define quota sample -Population divided into groups according to sampling frame -Interviewer selects quotas to reflect groups proportions
Advantages of quota sample -Small sample is still representative -Easy -Cheap -Comparable
Disadvantages of quota sample -Can introduce bias -Population divided into groups -Non responses not recorded
Define opportunity sample Sample taken from people at the time, who meet criteria
Advantages of opportunity sample -Easy -Cheap
Disadvantages of opportunity sample -Not representative -Dependant on researcher
What is the equation for a stratified sample Strata size x sample size/total population
What is the difference between qualitative and quantitative data Qualitative- Descriptive Quantitative- Numerical
What is the difference between discreet and continuous data Discreet- Only takes certain values Continuous- Takes all values
How do we find outliers Greater than Q3+k(Q3-Q1) Less than Q1-k(Q3-Q1)
Define cleaning the data Removing outliers
What do we plot for cumulative frequency diagrams End point against cumulative frequency
What is the equation for frequency density Frequency density=(Frequency x k)/Class width
When do we use a histogram Continuous data
When do we use a bar chart Discreet data
What do we comment on when comparing data -Measure of location -Measure of spread
What axis is the independent variable on X
What axis is the dependent variable on Y
Define bivariate There are pairs of values for two variable
Define causal relationship Change in one variables causes a change in the other
Define interpolation Estimating a variable within the data range
Define extrapolation Estimating a variable outside the data range
What is the purpose of a regression line To minimise standard deviation
When can we use regression lines For data within the data range
Define mutually exclusive If one event happens the other events can't happen
If events are mutually exclusive: P(A or B)= P(A)+P(B)
Define independent events One event has no effect on the other
If events are independent P(A and B)= P(A) x P(B)
Define random variable A variable whose value depends on the outcome of a random event
Define discreet uniform distribution All probabilities are the same
ΣP(X=x)= 1
When can you model a random variable with a binomial distribution -Fixed no of trials(n) -2 possible outcomes -Fixed probability of success (P) -Trials are independent of each other
P(X<Y)= P(X≤Y-1)
P(X≥Y)= 1-P(X≤Y-1)
P(X>Y)= 1-P(X≤Y)
Define test statistic The result of the experiment or the statistic that is calculated
Define null hypothesis The hypothesis you assume to be correct
Define alternate hypothesis Tells you about the parameter if your assumption is wrong
Define critical region A region of the probability distribution which if the test statistic falls within it would cause you to reject the null hypothesis
Define critical value The first value to fall in the critical region
What is the actual significance level The probability of incorrectly rejecting the null hypothesis
What are the steps of a one tailed hypothesis test -Formulate a model for test statistic -Identify suitable null and alternate hypotheses -Calculate the probability of test statistic being observed assuming null hypothesis is true -Compare to significance level -Write conclusion in context of question
What must you do for a two tailed hypothesis test Halve the significance level
If y+ax^n then logy= loga+nlogx
If y=kb^x then logy= logk+xlogb
What does the PMCC describe The strength and direction of the correlation
When can the PMCC be used If there is LINEAR correlation
If we are hypothesis testing for correlation what are the null and alternate hypothesis H0: p=0 H1: p≠0
How do we write, the probability that B occurs given that A has already occurred P(P|A)
What is the rule for independent events and conditional probability P(A|B)=P(A|B')=P(A)
P(A)+P(B)-P(A∩B)= P(A∪B)
(P(B∩A))/(P(A))= P(B|A)
What are the probability symbols for and and or And=∩ Or=∪
Created by: Liam P
 

 



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