choosing a statistical test

Question 1

what 3 factors are used to determine what statistical test is used?

Answer 1

1. whether researcher is looking for a difference or correlation / association
2. if a difference, what experimental design is being used
3. level of measurement

Question 2

decision 2: experimental design

Answer 2

• related designs: repeated measures, matched pairs
• unrelated: independent groups

Question 3

what are the 3 levels of measurement?

Answer 3

• nominal
• ordinal
• interval

Question 4

what is nominal data?

Answer 4

• data in the form of categories
• one item can only appear in one category (discrete)

Question 5

what is ordinal data?

Answer 5

• distance between units of measurement are not equal
• lacks precision as it is based on subjective opinion rather than objective measures

Question 6

how is ordinal data used in statistical testing?

Answer 6

raw scores are converted to ranks (ie. 1st, 2nd etc.) which are used in the calculation

Question 7

what is interval data?

Answer 7

• data on numerical scales that include equal, precisely defined size
• most precise and sophisticated form of data in psychology

Question 8

which statistical tests are parametric tests?

Answer 8

• related t-test
• unrelated t-test
• pearson’s r

Question 9

why are parametric tests used?

Answer 9

• more powerful and robust than other tests
• can detect signficance in some data sets that non-parametric tests cannot

Question 10

what 3 criteria must be met to use a parametric test?

Answer 10

1. interval data
2. data should be drawn from a population which would be expected to show a normal distribution for the variable being measured
3. homogeneity of variance: sets of scores in each condition should have similar dispersion

Question 11

how can you determine homogeneity of variance?

Answer 11

• compare standard deviations in each condition
• if they are similar, a parametric test may be used
• in a related design, it is general assumed that the 2 groups of scores have a similar spread

Question 12

nominal: measure of central tendency and dispersion

Answer 12

• CT: mode
• D: n/a

Question 13

ordinal: measure of central tendency and dispersion

Answer 13

• CT: median
• D: range

Question 14

interval: measure of central tendency and dispersion

Answer 14

• CT: mean
• D: standard deviation

Question 15

choose a test: nominal data, test of difference (unrelated design)

Answer 15

chi-squared

Question 16

choose a test: nominal data, test of difference (related design)

Answer 16

sign test

Question 17

choose a test: nominal data, test of association or correlation

Answer 17

chi-squared

Question 18

choose a test: ordinal data, test of difference (unrelated design)

Answer 18

mann-whitney

Question 19

choose a test: ordinal data (related design)

Answer 19

wilcoxon

Question 20

choose a test: ordinal data, test of association or correlation

Answer 20

spearman’s rho

Question 21

choose a test: interval data, test of difference (unrelated design)

Answer 21

unrelated t-test

Question 22

choose a test: interval data (related design)

Answer 22

related t-test

Question 23

choose a test: interval data, test of association or correlation

Answer 23

pearson’s r