Lecture 6 Flashcards
mean, SE, SD, median and plots
What can stats provide?
provide objective criteria for evaluating hypothesis, synthesize information, help detect patterns in data, help to critically evaluate arguments
what stats cannot provide?
tell the truth, compensate for poor design,
indicate clinical significance
examples of narrative data
gender, social status, profession, colour
numerical measurements examples
lab results, vital signs
what is a population
A population is any entire collection of people, animals, plants, or things from which we may collect data. It is the entire group we are interested in, which we wish to describe or draw conclusions about.
what is a sample
A sample is a group of units selected from a larger group (the population) for the study.
why we select samples for data analysis
• A sample is generally selected for study because the population is too large to study in its entirety. The sample should be representative of the general population. This is often best achieved by random sampling.
what is descriptive statistics
brief descriptive coefficients that summarize a given data set, which can be either a representation of the entire population or a sample of a population.
why descriptive statistics are important
we get acquainted with the data, calculate the outliers, asses assumptions needed to check statistical hypothesis, check that the data doesnt have any errors
describe nominal (categorical/qualitative) variable
values are in arbitrary (sutartinis)categories and no units
describe ordinal (categorical/qualitative) variable
values in ordered categories and no units
describe discrete (metric/quantitative) variable
integer (sveiki skaiciai), counted units
describe continuous (metric/quantitative) variable
continuous values, measured units
how can we systemise descriptive statistics
frequency and contingency tables, charts
how to summarise metric data
Mode, median, mean, quartile, variance, standard deviation
Asymmetry, kurtosis , Charts , histogram
what is a limitation of histograms
they can only represent one variable
how to write assumption of normality?
mean ± SD
what is mean
The mean is the arithmetic average of the observations
what is variance
the spread around the mean.
standard deviation
a quantity expressing by how much the members of a group differ from the mean value for the group.
why analysing only the mean is not accurate
• Analysing just the mean values is not as accurate, due to various values that could be present in the data set. Therefore we need to look at the variance of the data and SD to evaluate the accuracy.
what the empirical rule states?
The empirical rule states that for a normal distribution (bell shaped histogram), nearly all of the data will fall within three standard deviations of the mean.
the empirical rule
In particular, the empirical rule predicts that 68% of observations falls within the first standard deviation (µ ± σ), 95% within the first two standard deviations (µ ± 2σ), and 99.7% within the first three standard deviations (µ ± 3σ)
standard error definition
• The SD of the sample means, known as the standard error (SE), measures the deviation of individual sample means from the population mean. It measures the variability in the sample means.
