STATS- Data presentation/Data processing Flashcards
Explain how one can select a random sample of 10 different trees from the 200 trees
Allocate numbers 001 to 200 to the trees. Choose 10 (3 digit) random numbers from this - could use random number generator
How to work out outliers using mean and standard deviation
Upper Quartile —> Mean + 2 * s.d
Lower Quartile —> Mean - 2 * s.d
How to work out standard deviation
Root sum of x^2 - n(Xbar)^2 / n-1
How to work out variance
Sum x^2 - n(X bar)^2 / n-1
How do you plot a cumulative frequency graph
Use the final number - of the range
Add the frequency as you go along
Frequency is Y AXIS
Range is X axis
How to work out median and IQR from cumulative frequency graph
E.g. Median is 50% of total frequency.
Track and what number is on X axis
How to work out outliers using IQR and LQ/UQ
LQ - 1.5 * IQR
UQ + 1.5 * IQR
What does skewed mean
Data is concentrated on one side of the range
Low numbers (left) - Positive skew High numbers (right) - Negative Skew
What is formula for frequency density
FD = F/CW
What is simple random sampling
Every sample of size has an equal chance of being chosen
Needs a sampling frame
What are the advantages and disadvantages of simple random sampling
Advantages: - Free of bias - Easy and cheap - has an equal chance Disadvantages: - Sampling frame needed - Not suitable when population size is large
What is systematic sampling?
Required elements are chosen at regular intervals from an ordered list
What are the advantages and disadvantages of systematic sampling
Advantages - - Simple and Quick to use - Suitable for large samples Disadvantages- - A sampling frame is needed - Can introduce bias
What is stratified sampling?
The population is divided into distinct groups (e.g male and females) and a random sample is taken from each
What is the formula for stratified sampling?
Number Sampled = number in stratum / number in population * overall sample size
