AS Stats Flashcards
How do you work out the interquartile range?
Upper quartile (halfway between middle and end) - Lower quartile (halfway between start and middle)
What are the 3 different patterns a set of data could form?
- Symmetrical
- Positive skew
- Negative skew.
What does bi-variate mean?
2 variables.
How do you work out if a value is an outlier?
Upper: UQ + 1.5 x IQR
Lower: LQ - 1.5 x IQR
If the value is above the upper outlier value or below the lower one then it is an outlier.
What is H0?
The null hypothesis.
What is H1?
The alternative hypothesis.
When do we accept H0?
When the answer is > significance level.
When do we reject H0?
If the answer is < significance level.
What does each letter represent in X ~ B (n, p)?
- n = number of trials
- p = probability of success
- Ignore X and B.
How do you find the critical region?
Find the values of X where the probability > significance level.
What does P(X=r) = altogether?
1
What do r and X represent in P(X=r)?
- r = list of possible values
- X = actual outcome.
What are the 7 types of sampling?
- Opportunity sample
- Simple random sample
- Systematic sample
- Self-selected sample
- Stratified sample
- Cluster sample
- Quota sample.
What is the sampling frame?
A list of the population.
What is an opportunity sample?
- Taking samples from people who are available at the time and fit the criteria
- Easy in terms of time and money
- Can produce a biased sample due to the researcher choosing people from own social and cultural group
- Participants may decline and it becomes self-selected
- No sampling frame.
What is a simple random sample?
- Every member of the population has an equal chance of being chosen
- Involves choosing at random the samples, e.g. drawing tickets out of a box
- Isn’t always possible since you may not have a list of everyone in the population.
What is a systematic sample?
- Involves choosing individuals to form a sample
- For example, if the parent population was all year 11 students in a school, you would get an alphabetic list and choose every 10th one.
What is a self-selected sample?
- Individuals in the sample have chosen to be in it
- For example if someone responds to an advert to be included in the sample
- People volunteer
- Quick
- Not representative.
What is a stratified sample?
- If the parent population can be divided into subgroups, or strata, then stratified sampling ensures all strata are sampled
- If numbers sampled from each strata are proportional to the sizes of the strata, then this is proportional stratified sampling.
What is a cluster sample?
- If the population can be and is divided into subgroups representative of the population, a sample can be taken from one of these subgroups
- For example divided into towns or countries.
What is a quota sample?
- Similar to a stratified sample, but is specified in terms of the number of data items required within each stratum
- This is often used by interviewers, where the selection of samples is up to them
- Asking them if they meet the criteria.
When would a 2-tailed hypothesis test occur?
If the probability of an event has changed - it could have increased or decreased, so it is a 2-tailed test.
How would a 2-tailed hypothesis test be different?
- p would be not equal to, as opposed to greater or less than
- You have to divide the sig level by 2 as it is 2-tailed.
