research methods statistics

Question 1

what are the 3 criteria for choosing a statistical test

Answer 1

1. looking for a difference or a correlation / association?
2. is experimental design related (repeated measures / matched pairs) or unrelated (independent groups)
3. what is the level of measurement

Question 2

unrelated design

Answer 2

using independent groups

Question 3

related design

Answer 3

using repeated measures or matched pairs

Question 4

test of difference designs

Answer 4

• unrelated design

- related design

Question 5

test of difference, unrelated design producing nominal data.
what is the appropriate statistical test

Answer 5

chi- squared

Question 6

test for difference, unrelated design producing ordinal data
what is the appropriate statistical test

Answer 6

Mann- Whitney

Question 7

test for difference, unrelated design producing interval data
what is the appropriate statistical test

Answer 7

unrelated t-test

Question 8

test for difference, related design producing nominal data

what is the appropriate statistical test

Answer 8

sign test

Question 9

test for difference, related design producing ordinal data

what is the appropriate statistical test

Answer 9

Wilcoxon

Question 10

test for difference, related design producing interval data

what is the appropriate statistical test

Answer 10

related t- test

Question 11

test for association or correlation producing nominal data

what is the appropriate statistical test

Answer 11

chi- squared

Question 12

test for association or correlation producing ordinal data what is the appropriate statistical test

Answer 12

spearman’s rank

Question 13

test for association or correlation producing interval data

what is the appropriate statistical test

Answer 13

pearson’s rank

Question 14

chi- squared test

Answer 14

used as a test of both difference and association / correlation.
data items must be unrelated
- test of difference, unrelated design, nominal data
or
- test of association or correlation, nominal data

Question 15

mann - whitney

Answer 15

test of difference
unrelated design
ordinal data

Question 16

unrelated t-test

Answer 16

test of difference
unrelated design
interval data

Question 17

sign test

Answer 17

test of difference
related design
nominal data

Question 18

wilcoxon

Answer 18

test of difference
related design
ordinal data

Question 19

Related t test

Answer 19

test of difference
related design
interval data

Question 20

spearman’s rank

Answer 20

test of association or correlation

ordinal data

Question 21

pearson’s rank

Answer 21

test of association or correlation

interval data

Question 22

nominal data

Answer 22

categories
each item can only appear in one category. there is no order.
e.g people naming their favourite football team.

Question 23

ordinal data

Answer 23

placed in order, intervals are subjective
data is collected on a numerical, order scale but intervals are variable, so that a score of 8 is not twice as much as a score of 4
ordinal data lacks precision because it is based on subjective opinion rather than objective measures
there is no units
e.g asking someone to rate how much they like psych on a scale of 1 to 10 where 1 is do not like at all and 10 is absolutely love

Question 24

interval data

Answer 24

units of equal size
interval data is based on numerical scales that include units of equal, precisely defined size.
this includes observations in a observational stay (8 tallies is twice as much as 4 tallies) or any public units of measurement (time, temperature, length)

interval data is better than ordinal data because more detail is preserved as the scores are not converted to ranks

Question 25

what happens if the statistical test is not significant

Answer 25

the null hypothesis must be accepted
the null hypothesis states there is no difference or no correlation between the conditions
the statistical test determines which hypothesis (null or alternative) is true and thus we accept or reject.

Question 26

the null hypothesis is accepted or rejected based on what

Answer 26

particular level of probability
probability is a measure of the likelihood that a particular event will occur, where 0 is a statistical impossibility and 1 a statistical certainties in psychology but there is a significance level - the point at which the null hypothesis is accepted or rejected.

Question 27

what level of significance is used

Answer 27

0.05 or 5%

this means the probability that the observed effect occurred by chance is equal to or less than 5%

Question 28

the calculated value

Answer 28

the value you calculate from the statistical test. this is compared to the critical value

Question 29

what is the critical value

Answer 29

fund from the table of critical values at the 0.05 significance. based on probabilities
the calculated value is compare to the critical value

Question 30

how do you find the correct critical value ( 3 criteria)

Answer 30

• hypothesis one tailed (directional) or 2 tailed (non directional)
• number (N) of participants or degrees of freedom (df)
• level of significant (or p value) 0.05

Question 31

what is a type 1 error

Answer 31

the null hypothesis is rejected and the alternative hypothesis is accepted when the null hypothesis is true

this is an optimistic error or false positive as a significant difference or correlation is found when one does not exist.

Question 32

what is a type 2 error

Answer 32

the null hypothesis is accepted but in reality the alternative hypothesis is true
this is a pessimistic error or false negative

Question 33

why is a type 1 error is likely

Answer 33

is more likely to be made if the significance level is too lenient (too high e.g 0.1 or 10%)

Question 34

when is a type 2 error likely

Answer 34

more likely if the significance level is too stringent (too low e.g 0.01 or 1%) as potentially significant values may be missed

Question 35

what is an correlations

Answer 35

it illustrates the strength and direction of an association between 2 co-variables

Question 36

what is a positive correlation

Answer 36

co-variables rise or fall together

Question 37

what is a negative correlation

Answer 37

one co-variable rises and the other falls

Question 38

what are the differences between correlations and experiments

Answer 38

• in an experiment the researcher manipulates the IV and records the effect on the DV. In a correlation there is no manipulation of variables and so cause and effect cannot be demonstrated
• in correlation the influence of EVs is not controlled so it may be that a third untested variable is causing the relationship between the co-variables (called an intervening variable)

Question 39

evaluation of correlations

Answer 39

+ useful starting point for research. by assessing the strength and direction of a relationship, correlations provide a precise measure of how 2 variables are related. if variables are strongly related it may suggest hypothesis for future research
+ relatively economical. unlike a lab study, there is no need for a controlled environment and no manipulation of variables is required. correlations are less time-consuming than experiments
- no cause and effect. correlations are often present as causal when they only show how 2 variables are related. there may be intervening variables that explain the relationship
- methods used to measure variables may be flawed. for example, the method used to work out an aggression score might be low in reliability (observational categories might have been used). this would reduce the validity of the correlation study

Question 40

what are the measures of central tendency (3)

Answer 40

• mean
• median
• mode

Question 41

what is the mean (and evaluate)

Answer 41

arithmetic average, add up all the scores and divide by the number
+ sensitive. includes all the scores in the data set within the calculation. more of an overall impression of the average than median or mode
- may be unrepresentative. one very large or small number makes it distorted. the median or the mode tend not to so easily.

Question 42

what is the median (and evaluate)

Answer 42

middle value, place scores in ascending order and select middle value. if there are 2 values in the middle, the mean of these is calculated
+ unaffected by extreme scores. the median is only focused on the middle value. it may be more representative of the data set as a whole
- less sensitive than the mean. not all scores are included in the calculation of the median. extreme values may be important

Question 43

what is the mode (and evaluate)

Answer 43

most frequent or common value, used with categorical / nominal data
+ relevant to categorical data. when data is discrete i.e represented in categories. sometimes the mode is the only appropriate measure.
- an overly simple measure. there may be many models in a data set. it is not useful way of describing data when there are many modes.

Question 44

what are the measures of dispersion (2)

Answer 44

• range

- standard deviation

Question 45

what is range (and evaluate)

Answer 45

the difference between highest to lowest value (+1)
+ easy to calculate. arrange values in order and subtract largest from smallest. simple formula, easier than the standard deviation
- does not account for the distribution of the scores. the range does not indicate whether most numbers are closely grouped around the mean or spread out evenly. the standard deviation is a much better measure of dispersion in this respect

Question 46

what is standard deviation (and evaluate)

Answer 46

measure of the average spread around the mean. the larger the standard deviation, the more spread out the data are.
+ more precise than the range. includes all values within the calculation. a more accurate picture of the overall distribution of the data set
- it may be misleading. may hide some of the characteristics of the data set. extreme values may not be revealed, unlike with the range

Question 47

what is a normal distribution

Answer 47

symmetrical, bell shaped curve. most people are in the middle area of the curve with very few at the extreme ends.
the mean median and mode all occupy the same mid point of the curve

Question 48

what is a skewed distribution

Answer 48

distribution that lean to one side or the other because most people are either at the lower or upper end of the distribution

Question 49

what is a negative skew

Answer 49

most of the distribution is concentrated towards the right of the graph, resulting in a long tail on the left.
mode is the highest point of the peak then the median next to the left and the mean is dragged across to the left (if scores are arranged from lowest to highest)

Question 50

what is a positive skew

Answer 50

most of the distribution is concentrated towards the left of the graph resulting in a long tail on the right
the mode is the highest point of the peak, the median comes next to the right and the mean is dragged across to the right (if scores are arranged from lowest to highest)

Question 51

significance

Answer 51

the difference/ association between 2 sets of data is greater than what would occur by chance - coincidence or fluke.
to find out if the difference / association is significant we need to use a statistical test

Question 52

how do you calculate the sign test

Answer 52

(test of difference, related design - nominal data)
1. the core for condition B is subtracted from condition A to produce the sign of difference (either a + or a -)
2. the total number of + and the total number of - should be calculated
3. participants who achieved the same score in condition A and condition B should be disregarded, and deducted from the N value.
4. the S value is the total of the less frequent sign
if S is equal or less than the critical value, then S is significant and the experimental hypothesis is retained.