AS Revision Flashcards
Population
The whole set of items that are of interest
Sample
Some subset of the population intended to represent the population
Sampling Units
Individual units of a population that can be sampled
Sampling Frame
Sampling units of a population are individually named or numbered to form a list
Advantages of a Census
- should give a completely accurate result
Disadvantages of a Census
- time consuming and expensive
- cannot be used when testing involves destruction
- large volume to data to process
Advantages of a Sample
- cheaper and quicker
- less data to process
Disadvantages of a Sample
- data may not be accurate
- data may not be large enough to represent small sub-groups
Random Sampling
Each thing in the sampling frame has an equal chance of being chosen in order to avoid bias
Advantages of Random Sampling
- bias free
- easy and cheap to implement
Disadvantages of Random Sampling
- not suitable when population size is large
- sampling frame needed
- may not be representative
Systematic Sampling
Required elements are chosen at regular intervals in an ordered list
Advantages of Systematic Sampling
- simple and quick to use
- suitable for large populations
- no bias
Disadvantages of Systematic Sampling
- sampling frame needed
- bias can be introduced if sampling frame isn’t random
Stratified Sampling
Population divided into groups (strata) and a simple random sample carried out in each group
Advantages of Stratified Sampling
- reflects population structure
- guarantess proportional representation within population
Disadvantages of Stratified Sampling
- population must be clearly classified into distinct strata
- same disadvantages as simple random sampling
Quota Sampling
Use stratified sampling to divide population into strata
Actively choose people within each strata until the quota of each group is filled
Advantages of Quota Sampling
- no sampling frame needed
- quick, easy, inexpensive
Disadvantages of Quota Sampling
- can introduce bias
- population must be grouped into clear strata
Opportunity Sampling
Find people at the same time the survey is being carried out
Advantages of Opportunity Sampling
- easy to carry out
- inexpensive
Disadvantages of Opportunity Sampling
- unlikely to provide a representative sample
- highly dependent on individual researcher
Coding: Effect on Mean
Add/Sub = same effect
Div/Mul = same effect
Coding: Effect on Standard Deviation
Add/Sub = no effect
Div/Mul = same effect
Cleaning Data
Removing Anomalies
Frequency Density =
Frequency/Class Width
Casual Relationship
Two variables have a casual relationship if a change in one variable causes a change in the other
Least Squares Regression Line
Best line of best fit
y = a + bx
+ve b = +ve correlation
Probability
Mutually Exclusive Events: P(A and B) = 0
Independent Events: P(A and B) = P(A) x P(B)
Binomial Distribution
- fixed number of trials
- two possible outcomes
- fixed probability of success
- trials are independent
Hypothesis Test
- Let X be …
- H0: p=x H1:p>x p = probability of …
- Significance Level = 5% = 0.05
- X - B(n,x) P(X>/ z) = 1 - P(X< z-1)
- Compare Values
- There is/is not enough evience to reject the H0
- Make the statement in context
Two-Tailed Tests
Half the significance level
Derive SUVAT
Velocity Time Graphs
- gradient -> v = u+at
- area underneath -> s=1/2(u+v)t
- sub variables from v = u+at into s=1/2(u+v)t
