Presentation of Data

Question 1

what are the purposes of screening data

Answer 1

to detect blunders
locate outliers
determine distributional properties
determine number of missing values

Question 2

how is a small data set screened?

Answer 2

by eye

Question 3

how is a large data set screened

Answer 3

frequency table or histogram

Question 4

what are the 2 main types of variables

Answer 4

categorical and quantitative

Question 5

what are categorical variables

Answer 5

occur when individual falls into a category
divided into nominal (no ordering eg sex)
ordinal (have an ordering eg pain)

Question 6

what is the frequency distribution

Answer 6

frequency of the occurrence of different values of a variable

Question 7

what is relative frequency

Answer 7

frequency expressed as a proportion of the total frequency

Question 8

how are interval scale variables graphically presented

Answer 8

histograms or box plots

Question 9

what is a box plot

Answer 9

5 point summary of the data consisting of the minimum, 1st quartile, median, 3rd quartile and maximum valueas

Question 10

what do summary statistics attempt to capture

Answer 10

a typical value (the location) or the spread (or dispersion)

Question 11

what 2 measurements are used for location

Answer 11

mean and median

Question 12

what is mean

Answer 12

sum of all the observations divided by the total number of observations

Question 13

what is the median

Answer 13

middle value if a sample is arranged in increasing order. approx 50% of the sample is less than the median and 50% is greater than the median

Question 14

what summary statistics measure the spread

Answer 14

range, interquartile range, variance, standard deviation, coefficient of variation

Question 15

what is the range

Answer 15

difference between the largest and smallest observations in the sample - not recommended as it severely affected by outlying observations

Question 16

what is the interquartile range

Answer 16

difference between the 3rd and 1st quartiles

Question 17

what is variance (s2)

Answer 17

sum of the squared distance of each value from the mean, divided by the number of values - 1

Question 18

what is the standard deviation

Answer 18

the square root of the variance. used in preference to variance as is in the original scale of measurement

Question 19

what is the coefficient of variation defined by

Answer 19

c = s/x x100%
provides a measure of variation which is independent of the unit of measurement and hence can be used to compare the variation of variables measured on different scales

Question 20

what summary statistics are used if the distribution is roughly symmetrical

Answer 20

mean and std deviation

Question 21

what summary stats are used if the distribution is skewed

Answer 21

median and interquartile range