Stats

Question 1

SD & ND

Mean (average)

Answer 1

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

Question 2

SD & ND

Variance

Answer 2

How far each number in the data set is from the mean. Subtract the “x” value from the mean, square the output, then divide by n.
(x - Mean)^2 / n

Question 3

SD & ND

Standard deviation

Answer 3

Standard deviation is simply the square root of the variance and gives an idea of how spread out the values in a data set are around the mean.

Question 4

SD & ND

Normal distribution

Answer 4

• A probability distribution that is symmetric around the mean.
• In a graph, it looks like a “bell curve.”
• The mean, median, and mode of a normal distribution are equal.

Question 5

SD & ND

Key features of normal distribution

Answer 5

• 68% of data falls within one standard deviation of the mean (μ ± σ)
• 95% of data falls within two standard deviations (μ ± 2σ)
• 99.7% of data falls within three standard deviations (μ ± 3σ)

Question 6

SD & ND

Z Score

Answer 6

Tells you how many standard deviations it is away from the mean:

Z = (x − μ) / σ

Question 7

SD & ND

A smaller standard deviation indicates…

Answer 7

Data is more tightly clustered around the mean/is more consistent

Question 8

SD & ND

A larger standard deviation indicates…

Answer 8

Greater variance in the data set

Question 9

SD & ND

How does the data change if you change the mean?

Answer 9

If you add a constant to every data point, the mean would shift by that constant, but the standard deviation would stay the same

Question 10

How does the data change if you change the standard deviation?

Answer 10

Multiplying each score by a constant would scale the standard deviation by the absolute value of that constant. E.g., if you double every score, the new standard deviation would be 2 x SD = 2SD. So, e.g., if SD = 1.41, then 2 x 1.41 = 2.82

Question 11

Is it possible to make predictions about other percentiles?

Answer 11

No

Question 12

Box and whisker plot

Answer 12

Middle line in the box represents the median, or middle, of the dataset. The outsides of the box are the medians of the data below and above the median, respectively, which mark the first and third quartile boundaries, or Q1 and Q3

Question 13

Interquartile range

Answer 13

Distance between Q1 (median of the first half of the dataset) and Q3 (median of the second half of the dataset)

Question 14

T/F: Normal distributions are always centered on and symmetrical around the mean

Answer 14

True

Question 15

For any evenly spaced set..

Answer 15

The median equals the mean