Lesson 10 rm psych stats & graphs 2013

Research Methodsin Psychology

Statistics

Lesson 10:

Saturday, 20 April 13

Lesson 9EXAM QUESTION

Taken from VCAA 2011 Mid Year ExamSaturday, 20 April 13

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Lesson 10: Statistics

* Define descriptive statistics * Define inferential statistics * Describe the types of statistics in Psychology:- calculate measures of central tendency including mean, median and mode-interpret p-values and draw conclusions -evaluate research in terms of generalizing the findings to the population

What you need to know and be able to do


Generalising Results

To be able to generalise results, the following criteria must be met:

The results show statistical significance (p<0.05)

All sampling procedures were appropriate

All experimental procedures were appropriate

All measures were valid

All possible confounding variables were controlled.


Types of Statistics

In psychology there are two types of statistics

1) Descriptive Statistics, show results

2) Inferential Statistics, explains results in relation to hypotheses.


Descriptive statistics

Test A -1,7,22,66,4,3,55,44,5,6,78,789,23,1,23,

Test B -67,43,67,678,33,21,45,76,89,09,3,3,23,

Who would you describe this data?


Descriptive statistics

Descriptive statistics are used to summarise, organise and describe data obtained from research

Test A -1,7,22,66,4,3,55,44,5,6,78,789,23,1,23,

Test B -67,43,67,678,33,21,45,76,89,09,3,3,23,

Who would you describe this data?


Descriptive Statistics

1) Percentages

2) Measures of central tendency

3) Spread of scores

4) Measures of Variability

5) Graphs and tables (Later in the AOS)


Calculating the percentage

Number of times score occurs DIVIDED BY Total number of scores in data set MULTIPLIED BY 100

E.G. The percentage of rolling a 6 would be:

13/80 = 0.1625 x 100 = 16.25%


Tells us how the data are clustered near the central point of the dataset.

There are three measures of central tendency 1) Mean - average of all the scores (calculated by adding up all the scores and dividing that total by the number of scores) 2) Median - the score that occurs exactly halfway between the lowest and the highest score. 3) Mode - the most commonly occurring score in the dataset.

2) Measures of Central Tendency(Measures in the Bell Curve)


3) Spread of scoresAnother way of describing data is by looking at how the scores are spread. This is known as variability. This can be done by

Range - The range of data can be calculated by subtracting the lowest score from the highest score

Standard deviation - How far is each individual piece of data from the mean. A low standard deviation indicates the scores cluster around the mean


Complete Check your understanding questions on page 23 (RM book) - 10 min


Inferential StatisticsInferential Statistics are used once the descriptive statistics have identified there is a difference (variation) from the mean. (Read page 30 of RM book)

What next is to determine if this difference or variance is significant, or is it just due to chance.

Inferential tests give a probability that the difference is caused by chance.

This is expressed as a p value.

Generally the lower the p value the better, however p<0.05 (that is 5 times in 100 or 5% of the time it is due to chance) is widely accepted.


p = 0.03 means there are 3 chances in 100 (3%) that this difference would be achieved by chance

alone.

If the level of significance is p<0.05 then these results can be said to be statistically significant as it

is less then (<) 0.05

If the p value = 0.3 then the results are not significant as 0.3 is greater then 0.05.


Complete questions on page 31 (RM book) 10 min


Lesson 10 rm psych stats & graphs 2013

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