ch. 3, descriptive stats

central tendency

a single score that defines the centre of a distribution

• this measure is intended to be the most representative score for your group

list 3 measures of central tendency

1. mean

2. median

3. mode

mean

average score of the group. add all the scores divided by the number of scores

mean is best used for

interval/ration data - because each score contributes to the mean

when is mean not useful

in data sets with extreme scores

2 symbols for means

• M or x̄ = used for sample data

• μ = used for population means

how do we calculate the mean?

calculation for weighted mean

median

the middle score/ mid point. it divides the scores into 2 equally sized groups

4 things median is used for

1. extreme scores

2. undetermined values (such as participants who cannot finish a task in the time alloted)

3. open ended scores

4. ordinal scales

calculating media for even and odd scores

calculating for odd scores: order the scores from smallest → largest, the middle score is the median

calculating for even # of scores: find the two middle scores & take the average (add then divide by 2)

mode

the score or category that has the highest frequency (most frequent score)

mode is often used for

nominal scales

draw the curve for positively skewed data

draw the curve for negatively skewed data