Lecture 2 Flashcards
(32 cards)
What is Sampling?
Drawing various quantities of scores from a population
What is the shape of a normal distribution?
Central peaks that fall away symmetrically on either side
Also referred to as a ‘bell shape’
What are histograms used for?
Examining the frequency of scores within certain intervals (groups of scores)
They group scores into bands depending on data spread
What does the Central Limit Theorem state?
Larger samples will better approximate a normal distribution
More data points lead to a closer approximation of the true population mean
What are descriptive statistics?
We use descriptive statisctics to summarise distributions
help quantify central tendency and spread of distribution
(mean, median mode, etc.)
What is the most popular measure of central tendency?
Mean
It is easy to calculate and useful for summarising groups of values
What is a median?
The midpoint of the dataset
Useful when the mean is inappropriate due to outliers or skewed data
What is the mode?
The most frequent value in the dataset
Almost never used in practice
What is the range in measures of variability?
The difference between the smallest and largest value in the dataset
What is variance?
The sum of the squared differences between each data point and the mean, divided by the sample size
Find mean > subtract mean from each data point > square each differnce > add all sqaured differnces > divide by sample size
What is the standard deviation?
The square root of the variance
It resembles an average difference score and is popular in psychology
How do you calculate variance?
Find mean > subtract mean from each data point > square each differnce > add all sqaured differnces > divide by sample size
What does a standard deviation of 14 cm indicate in the context of height in Australian women?
The standard deviation is reasonably small due to a large sample size
What does it mean when the standard deviation is larger than the mean?
It indicates a concerning distribution
Suggests that the data may have extreme cases or outliers
Negative vs Postive Skew
positive skew - tail on the right
negative skew - tail on the lft
Positive skew has a long tail in the positive direction
What is skewness?
A measure of the asymmetry of the distribution
Skew values should be less than 2
What is kurtosis?
A measure of how flat or pointy the distribution is
kurtosis values should be less than 9
How can outliers affect statistics?
They can be particularly problematic in small samples and influence the mean and standard deviation
What criteria can be used to identify outliers?
Scores which are 3 or more standard deviations away from the mean
What is the formula for creating thresholds?
Mean +/- 3 x (SD)
Females = 544.28 + 3 (541.66) = 2169.26 mins (36 hours on social media)
One negative - mean and SD are already influenced by outliers
What is the importance of interpreting descriptive statistics?
It helps derive meaning from data and compare it to prior studies or statistical reports
What types of data are best presented as frequencies or percentages?
Data such as gender and sample size
What are the minimum criteria for describing a sample in research papers?
Age and gender
What is the purpose of Z scores?
To understand the relative position of a case within a distribution
