descriptive stats

Question 1

What 3 factors should you try to encompass when designing a study

Answer 1

Types of data
If looking for difference or relationship
Number of groups or variables

Question 2

what are the 2 types of data

Answer 2

measurement and categorical

Question 3

what is measurement data

Answer 3

frequency or quantitative data

Question 4

what is categorical data

Answer 4

qualitative data

Question 5

what are the 4 types of scales

Answer 5

nominal
ordinal
interval
ratio

Question 6

what is a nominal scale and when is it used

Answer 6

used for categorical data which reflects labels for categories

Question 7

why shouldn’t you calculate summary descriptions for categorical data

Answer 7

results in nonsensical data

Question 8

define ordinal scales and what they’re used for

Answer 8

ordering objects along continuum of various rankings

no information given on differences btwn scale points

Question 9

give an example of a study using ordinal scales

Answer 9

Holmes and Rahe 1967

Question 10

define interval scales and what they’re used for

Answer 10

used when have equal intervals btwn objects to represent equal differences
do not allow talk on ratios as 0 point on scale is arbitrary

Question 11

define arbitrary

Answer 11

not based on system or re

Question 12

define ratio scales and what they’re used for

Answer 12

have true zero point

true zero corresponds to absence of thing being measured

Question 13

what are the aims descriptive statistics

Answer 13

to characterise numerical dataset representatively
to condense meaningful a lot of info
minimise error involved in condensing process

Question 14

what are inferential statistics

Answer 14

goal to infer characs of whole pop from sample and make likely assertions from information instead of certain ones
use sample stats to estimate population parameters
use of theoretical sampling distributions made of innumerable random samples
uses p-values and confidence intervals

Question 15

what are the 3 categories of descriptive statistics

Answer 15

measures of central tendency and measures of dispersion

Question 16

what are the 3 measure of central tendency

Answer 16

mean
median
mode

Question 17

what are the measures of dispersion

Answer 17

range
IQR
variance
standard deviation

Question 18

what is the mean; give the equation

Answer 18

average score; calculate by sum of scores/number scores

Σ x / N

Question 19

When is the mean most useful and why

Answer 19

For normal/symmetric distributions, the mean is the most efficient and least subject to sample fluctuations

Question 20

what are the disadvantages of using the mean

Answer 20

greatly influenced by extreme scores

Inaccurate sometimes

Question 21

how can you tell if the mean is an appropriate measure to use on a dataset

Answer 21

by using a histogram to see if data is symmetrical and if mean is appropriate

Question 22

what type of distribution is unsuitable for the mean

Answer 22

skewed distributions

Question 23

why is the median

Answer 23

when all scores arranged in order; central value

Question 24

why and when is the median useful

Answer 24

less sensitive extreme scores; gives more accurate representation of data
better measure than mean for highly skewed distributions.

Question 25

what is median formula

Answer 25

N+1/ 2

Question 26

define mode

Answer 26

most common score

Question 27

what happens if you have 2 adjacent modes

Answer 27

add them/2

Question 28

what happens if you have 2 nonadjacent modes

Answer 28

bimodal distribution

Question 29

what are the 2 defining features of measures of central tendency

Answer 29

they indicate typical values and are summarised by a single number

Question 30

what are the suitable summary descriptions for categorical data

Answer 30

frequencies percentages mode

Question 31

what are measures of variability

Answer 31

describe degrees to which values vary

Question 32

what is the range and how is it computed

Answer 32

measure of distance from lowest to highest score; max value- min value

Question 33

what are the disadvantages of using range

Answer 33

extreme values/ outliers distort | unstable across diff samples

Question 34

what is the real advantage of range

Answer 34

straightforward to calculate and easy to interpret

Question 35

what is the IQR, what does it use and how is it calculated

Answer 35

1/2 the distance needed to cover 1/2 the scores it uses percentiles It is computed as one half the difference between the 75th percentile [often called (Q3)] and the 25th percentile (Q1). The formula for semi-interquartile range is therefore: (Q3-Q1)/2.

Question 36

what is the difference btwn IQR in a normal vs skewed distribution

Answer 36

In a symmetric distribution, an interval stretching from one semi-interquartile range below the median to one semi-interquartile above the median will contain 1/2 of the scores. This will not be true for a skewed distribution, however.

Question 37

what are the advantages of IQR and what kind of distribution is it useful in

Answer 37

little affected by extreme scores; good measure of spread for skewed distributions.

Question 38

what is the calculation for the separate IQR/percentiles

Answer 38

percentile/100 first, e.g. 50th percentile= 0.50 then 0.50 * (N+1) = rank X then go across dataset and find number at rank position

Question 39

what is the disadvantage for IQR in normal distributions

Answer 39

more subject to sampling fluctuation in normal distributions than the standard deviation and therefore not often used for data that are approximately normally distributed.

Question 40

define variance

Answer 40

measure of how much scores vary in terms of distance from mean average of each score's squared deviation from mean score

Question 41

what is variance formula

Answer 41

σ2= Σ (x- MEAN)2 / N

Question 42

how does variance formula change when computing for sample vs population

Answer 42

N-1 for sample | N for pop

Question 43

when do you use sample variance formula

Answer 43

when have done sample and want to generalise to wider population and so estimate population variance

Question 44

what is standard deviation

Answer 44

square root of variance

Question 45

what does a bigger SD value mean

Answer 45

values more spread out

Question 46

what is the equation for sample and population SD

Answer 46

Population σ = √σ2 | Sample s = √s2

Question 47

what can you do if you know the SD and mean in normal distribution

Answer 47

possible to compute the percentile rank associated with any given score

Question 48

in a normal distribution, how many of the scores are within 1 SD of the mean

Answer 48

68%

Question 49

in a normal distribution, how many of the scores are within 2 SDs of the mean

Answer 49

95%

Question 50

why is SD useful

Answer 50

used in many inferential stats tests

Question 51

what is a disadvantage of the SD and how can this be overcome

Answer 51

not a good measure of spread in highly-skewed distributions | supplement by the IQR.