Descriptive Statistics Flashcards
“Samples and Populations”
What is a population?
A group that contains ALL people or objects with characteristic in common
“Samples and populations”
What is a sample?
researcher’s selection from the population
“Samples and populations”
Why do researchers use sampling?
Cheaper
quicker
convenient
“Samples and populations”
Before conducting research, what must the researcher insure?
Population is relevant to the sample
sample is truly representative of target population
“Samples and populations”
What do we use descriptive statistics for?
Describing samples
“Samples and populations”
Do you use inferential statistics for?
Generalising samples to wider populations
“Measures of Central Tendency”
What are measures of central tendency?
Data that indicates the typical score in the data set
“Measures of Central Tendency”
What are the three types of central tendency?
Mean
median
Mode
“Measures of Central Tendency”
How to calculate the mean?
Add up all the sample Scores
Divide by how many scores are in the sample
“Measures of Central Tendency”
How to calculate the median?
The middle value when sample scores are ordered
“Measures of Central Tendency”
How to calculate the mode?
The most frequently occurring score
“Measures of Central Tendency”
Which central tendency should be used When?
The mean is most frequently used.
You should use it when satisfied that scores Are typical of the sample
“Measures of Central Tendency”
What is an issue with the mean? How can it be resolved?
Sensitive to extreme scores
Use the medium instead
“Measures of Central Tendency”
What are outliers?
Extreme Scores in the Sample
Considerably higher or lower then other scores
“Measures of Central Tendency”
How to find outlier on box plot?
School outside hinges of box
Number above Whiskers on box plot Show which score Is extreme
E.g. 10 equals tenth score is extreme
“Measures of Central Tendency”
To do If there’s an outlier?
check data entered is correct
was there anything unusual that explains it in data collection
e.g participant did not finish
“Measures of Central Tendency”
And you remove outliers from the data?
Yes if there is a legitimate reason - not if theres no reasoning
say that you removed it in report
“Normal Distribution”
why do we look at normal distribution?
used to make assumption about a populations distribution
“Normal Distribution”
What does normal distribution and require? (3)
- Symmetrical about the mean
- Tales meet x-axis at infinity
- Bell shaped
“Normal Distribution”
What are all the same normal distribution?
Mean medium and mode
“Normal Distribution”
What is needed to plot normal distribution?
Function of the mean
Standard deviation
“Normal Distribution”
What is normal distribution?
Distribution of scores that creates a bell shape
“Normal Distribution”
how does normal distribution become “perfect”?
modes of mean, median and mode are all represented by the peak
“Normal Distribution”
what does sample size have to do with normal distribution?
larger sample sizes represent distributions better because of the clearer peak
“Variation or spread of distributions”
what is variation?
The the degree that the score of a variable is different to another
“Variation or spread of distributions”
What is used to understand variation?
The range
“Variation or spread of distributions”
How to calculate the range?
Take away the smallest value from the largest value
“Variation or spread of distributions”
What does the range do?
Tells us about a overall range of scores
“Variation or spread of distributions”
What is a limitation of the range?
Does not tell us about overall shape of distribution of the sample
“Variation or spread of distributions”
What is standard deviation?
Square root of variance
“Variation or spread of distributions”
what does standard deviation do?
Measures how much data deviates around the mean
“Variation or spread of distributions”
why is SD Better than the range?
Indicates what is happening between two extremes
which tells the variation around the mean
“Variation or spread of distributions”
why is standard deviation an important method?
Basis for most statistic techniques to analyse data
“Variation or spread of distributions”
what is the problem with mean deviation?
Only measures Central tendency
half of deviations will be negative numbers
-When added they will become zero
“Variation or spread of distributions”
How to resolve the problem with mean deviation?
Square each deviation from the mean
(Negative become positive)
Calculate the mean of squared deviations - This is variance
“Variation or spread of distributions”
What is the issue with variance?
The squared deviation is not expressed in same unit as the original school
must square root variance to achieve this
