RDS Calculations and Formulae Flashcards Preview

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

Flashcards in RDS Calculations and Formulae Deck (9)
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1

Mean

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

Sum (x) / n

2

Median

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

3

Mode

Most frequently occurring data point

4

Variance

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)

5

Standard deviation

Square root of the variance

Given as σ or s (population/sample)

6

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

7

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

8

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

9