chapter 2 stats Flashcards
What is the correct notation for x?
Sigma of x/n= x bar
How do you calculate the mean of a grouped frequency table.
Sigma frequency X x/ sigma frequencies.
When you are calculating median or quartile what should you do if you get a decimal?
Always round up.
How to work out the variance?
The mean of the squares minus the square of the mean.
What is the difference between variance and standard deviation.
standard deviation is the square root of the variance.
What is the main difference between adding and subtracting when coding and then multiplying and dividing?
coding by adding and subtracting will only change averages.
BUT not measures of spread.
Coding by multiplying and dividing will change both averages and spread.
How do you calculate the mean when you have two different means and the number of observations in each of them?
Multiply the mean by the number of observations to find sigma x.
Then add the sigma x of both and add the number of observations of both and divide them
How to calculate the median?
n/2 if it is decimal round up and this is the corresponding term
If it is whole number use this and number above to find midpoint.
Pro and con for mode?
Pro- can be used for both qualitative and quantitative data.
Con- There is no mode if each value appears with the same frequency
Pro and con for median?
Pro- unaffected by anomaly or outlier.
Con- it does not use every data value in the set
Pro and con for mean?
Pro- all values within the data set are used.
Con- can be skewed by anomalies.
How to work out lower quartile and upper quartile?
Lower quartile is n/4 (if it is a decimal round up, if it is whole use that number and the following to find midpoint.)
Upper quartile 3n/4 (if it is a decimal round up, if it is whole use that number and the following to find midpoint.)
How to calculate the mean of a grouped frequency table?
frequency times x / total frequency.
What is important when working with grouped frequency tables?
Think about the lower and upper bounds if it has been rounded.
What is the formula for linear interpolation?
Lower Bound + ( depth intro group/ group frequency) x Class width of group.
When do you round for group tables and where do you not?
For continuous data you use rounding for discrete you do not.
What does the IQR do?
It measures the spread of the middle 50% of data.
How do you calculate variance?
The mean of the squares - the mean squared
How do you calculate standard deviation?
What is an alternative way of calculating standard deviation?
square root of sxx over n
What is standard deviation?
It is a measure of spread and looks at the average distance of each data point from the mean.
What is the difference between standard deviation and variance?
Standard deviation is the root of the variance.
What must you do when finding the standard deviation of grouped frequency?
Use the midpoint as the x value.
What is one standard deviation above the mean?
mean + standard deviation.
Why is coding useful?
if data in a set is particularly large they can be made simpler.
What impact will coding have on measures of spread and measures of average if you add or subtract.
For measures of spread it will have no impact.
For averages
What is different when encoding measures of spread?
You must only divide or multiply you do not need to add or subtract to reverse.
How could you use sxx In data?
Divide by n and square root to find standard deviation.
