Measurements

Question 1

What is measuring ?

Answer 1

Assigning a number to some property of an individual

Question 2

Measured value =

Answer 2

true value + bias + random error

Question 3

What is bias?

Answer 3

systematical overstating or understating of measurements

Question 4

What is a random error? How do you minimize it?

Answer 4

Repeated measurements give different results

average of several measurements is more accurate than single one

Question 5

What is variance? what does it measure ?

Answer 5

Variance = average of squared differences from the mean

measures the reliability of measurement

Question 6

What is distribution ?

Answer 6

function that shows the possible values for a variable and how often they occur (frequency)

Question 7

What is the mean ?

Answer 7

average, sum of all numbers divided by total number of data points

Question 8

Give characteristics of Mean

Answer 8

• only for numerical data
• good for normally distributed data
• distorted by outliers

Question 9

What is the median?

Answer 9

Middle value when data is arranged in increasing order (works for both ordinal & numerical data)

Question 10

what is the mode?

Answer 10

Value that appears most in data set

Question 11

Give characteristics of mode

Answer 11

• works for all type of data
• dataset can be multi modal
• useful when you have a large sample

Question 12

Range =

Answer 12

largest # in data set - smallest # in dataset

= distance between 2 extremes

Question 13

What is interquartile range ? How is it calculated ?

Answer 13

looks at spread of middle 50% of data

IQR = Q3 - Q1

Question 14

What is standard deviation ?

Answer 14

Square root of variance, average amount we expect a point to differ from the mean

Question 15

What is standard score?

Answer 15

nb of SD by which a value is above or below the mean

Question 16

Why are Zcores used?

Answer 16

allows us to compare standard score for things that are not on the same scale as long as they are normally distributed

Question 17

Zscore =

Answer 17

(raw score - means core) / SD

Question 18

Raw score =

Answer 18

Zscore * SD + mean score

Question 19

What is a density curve? Why do we used density curves?

Answer 19

visualisation of distribution where the variable can take any value
intended to reflect the idealized shape of population distribution as opposed to simply a sample

Question 20

give characteristics of density curve

Answer 20

• entire area under curve is 1
• median = equal area point
• mean = point where curve would balance

Question 21

Left Skew

Answer 21

= Negative skew

• tail on the left (outliers)
• most of data on right
• mean > median

Question 22

Right skew

Answer 22

= Positive skew

• tail on the right (outliers)
• most of data on left
• median > mean

Question 23

What is normal distribution ?

Answer 23

distribution symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean
=> represented by bell curve

Question 24

characteristics of bell curve

Answer 24

• symetric
• unimodal, single peaked
• SD = distance between mean & change of curvature point
• mean = median = mode

Question 25

Explain the 68-95-99.7 rule

Answer 25

• 68% of observations are within 1 sd of the mean
• 95% of observations are within 2 sd of the mean
• 99.7% of observations are within 3 sd of the mean

Question 26

List 5 numbers of 5 numbers summary

Answer 26

• minimum
• 1st quartile
• median
• 3rd quartile
• maximum