RDS Calculations and Formulae Flashcards Preview

Y2 - Research Design and Statistics > RDS Calculations and Formulae > Flashcards

Flashcards in RDS Calculations and Formulae Deck (9)
Loading flashcards...


Sum of all data values divided by the number of data values

Sum (x) / n



Add 1 to the number of data values

Divide this by 2 

Take the value associated with the data value found

e.g. 15 values, + 1 = 16/2 = 8

take value of 8th data point

For even values e.g. 16 +1 = 17/2 = 8.5

Take mean of 8th and 9th values



Most frequently occurring data point



Sum of (x - mean)2 (each individual bracket is squared and then summed)

All divided by n (for population) or n-1 (for sample)

Given as σ2 (population) or s2 (sample)


Standard deviation

Square root of the variance

Given as σ or s (population/sample)


Standard error

Can only be calculated for a sample (not population)

s (standard dev) divided by square root of n

standard deviation of the sample divided by the square root of the number of values in the sample


Interquartile range

Value for lower quartile subtracted from value for upper quartile (this is the range remember)

This is another measure of dispersion of data


Example, you are given systolic blood pressure (in mmHg) for a sample of males and females. How would you go about using descriptive statistics to start describing the data?

Look for a measure of central tendency and of data dispersion.

Central tendency = mean

Dispersion = SD

Since it's a sample it would be appropriate to also include the standard error of the mean

So in total, mean, SD, SEM