4.2.3.3 PROBABILITY AND SIGNIFICANCE

Question 1

what are psychologists interested in finding out about their results or their studies?

Answer 1

if they show real differences or correlations, or if the results are due to chance factors
eg. the probability of the IV having affected the DV

Question 2

how do psychologists determine whether results are significant?

Answer 2

to determine whether they’re significant and not due to chance factors

• researchers use a measure of the level of significance

Question 3

what must researchers decide to conclude that the observed result is unlikely to be due to chance?

Answer 3

must decide how long an effect or relationship is required

this decision is reflected in the level of significance applied to the data

Question 4

how is the level of significance expressed?

Answer 4

as a decimal value where ‘p’ stands for the probability that chance factors are responsible for the results

Question 5

for most purposes in psychology, what level of significance is appropriate?

Answer 5

the 5% level of significance is appropriate which is expressed as p<0.05
ie) the probability of chance factors producing the observed result is less than or equal to 5%

Question 6

how is the critical value found?
what does this determine?

Answer 6

the research will use statistical tables to find the critical value

• this will determine whether or not they can reject the null hypothesis

Question 7

what are inferential statistics?

Answer 7

• enable us to draw inferences about the population
• designed to tell us the likelihood that the IV affected the DV
• refer to a probability factor of less than 0.05 (conventional level)
  -> 5% or less, likely that a chance factor affected the DV
  -> 95% or more, likely IV affected DV
• can go lower for things like drug trials
  -> ‘p’ is less than 0.01

Question 8

what are descriptive statistics?

Answer 8

• show patterns / trends in data of the sample taken from that population
• measures of central tendency
  -> average, mean, median, mode
• measures of dispersion
  -> spread in data, range, standard deviation, spread of data around the mean
• don’t tell us anything about it affecting the DV

Question 9

when is an observed value gained?
what needs to happen with it?

Answer 9

• once the researcher has conducted a statistical test they have an observed value which is used to determine whether results are significant
• this observed value needs to be compared to the critical value in the statistical tables

Question 10

what is a Type I error?

Answer 10

• they occur when the null hypothesis is rejected when it should have been accepted
  ie) the researcher claims that the results are significant when in fact they’re not (aka a ‘false positive’)
• more likely to happen when the researcher uses a probability value that’s too high
  eg) 0.1 rather than 0.0.5

Question 11

what is a Type II error?

Answer 11

• occur when the null hypothesis is accepted when it should’ve been rejected
  ie) the researcher claims that the results aren’t significant when in fact they are (aka ‘false negative’)
• more likely to happen when the researcher uses a probability value that’s too low
  eg) 0.01 instead of 0.05

Question 12

what 3 things are needed to be considered in order to choose a stats test?

Answer 12

1) test of difference or association
- difference = experiment, IV, DV
- association = correlation, 2+ co-variables
2) experimental design
- independent groups = unrelated data
- matched pairs and repeated measures = related data
3) level of data
- nominal data
- ordinal data
- interval data