Statistics and Visualisation with R #3
Post number three of my notes from a course on Statistics and (data) Visualisation with R, presented by Lucia Michielin of the University of Edinburgh in June and July.
- Programme overview
- Class 5 - Data Collection Bias, Probability, and Distribution
- Class 6 - Hypothesis testing and the main tests
- Playtime discoveries
- Next steps: other ways to learn R
- Notes and references
|Class||Date and time||Title|
|Class 1||01 June 13:00-14:30||Intro to R and R studio|
|Class 2||02 June 13:00-14:30||Types of data and Grammar of graphs|
|Class 3||08 June 13:00-14:30||Intro to statistics and descriptive stats|
|Class 4||09 June 13:00-14:30||Boxplot and playing with Colours|
|Class 5||15 June 13:00-14:30||Data Collection Bias, Probability, and Distribution|
|Class 6||16 June 13:00-14:30||Hypothesis testings and the main tests|
|Class 7||22 June 13:00-14:30||Barcharts and cleaning the sample|
|Class 8||23 June 13:00-14:30||PCA and Cluster analysis|
|Class 9||29 June 13:00-14:30||Covariance, Regression, Similarity and Difference coefficients|
|Class 10||30 June 13:00-14:30||Recap and Bring your dataset class|
Class 5 - Data Collection Bias, Probability, and Distribution
After a quick review of the challenge from last week, an agenda for today was shared which wasn’t really followed1.
Data Collection and bias
“Data collection is the process of gathering and measuring information on targeted variables in an established system, which then enables one to answer relevant questions and evaluate outcomes. The goal for all data collection is to capture quality evidence that allows analysis to lead to the formulation of convincing and credible answers to the questions that have been posed.” (Wikipedia)
The sample is taken from the population, but a bias is introduced when the sample is taken. One example of this is the survivorship bias.
A basic definition was given to the class, with an example from an earlier class that helped us. If we make the statement
if **A** is true then **B** is true can we infer from this that
if **B** is true then **A** is true? Clearly not, but we might be able to say
if **B** is true then **A** is more plausible. Plausibility here relates to how probably something can be.
“Probability is a numerical description of how likely an event is to occur or how likely it is that a proposition is true.” - Wikipedia
In introducing this topic, we were shown the really neat
rnorm() function that generates random data sets with specified mean and standard deviation.
In the class, we were given a challenge to go through the steps needed with a new data set to examine it. These steps seem to be just to plot it and have a look. All of the curves looked to be distributed around a central mean, which makes them normal distributions. There was a problem with the challenge files which meant that some of us didn’t have the correct files and so did a different (trivial) task. The key message is to examine your data as soon as you have it, to look for central values and distribution, so as to understand it and how you expect it to behave in analysis.
Other distributions include uniform, logarithmic, left-, right-skewed and bimodal.
Class 6 - Hypothesis testing and the main tests
Just half a dozen students today. We started with a review of the mini-challenge from last session, which included a consideration of colours: HTML colour and a ggplot colour reference were shared.
One emphasis today is that there are multiple ways of doing the same thing in R, with an illustration of data importation and summarisation. Although some of the few remaining students seemed to be following the narrative, I became increasingly frustrated and lost trying to follow the class: the thread was along the lines of hypothesis testing, the null hypothesis and corrections.
Between this week’s two classes, I had a quick look at the Comprehensive R Archive Network (CRAN) and discovered a neat thing. Remember the funky assignment operator
<- from the first class which had its funky keyboard shortcut
alt -? Most programming languages I’ve used have a simple equals sign as the assignment operator and I was a bit baffled as to why super-sexy R should do something so weird as
<-. Well, it turns out that in most contexts,
= works in exactly the way you’d expect, so these are equivalent:
> x <- 99 > x = 99
What’s interesting about the R syntax, though, it that it can be reversed and it still works:
> 99 -> x
I’m sure that the case for this will become apparent eventually. One more way to do assignments is to call the assignment function:
> assign('x', 99) # notice the weird need for quotes around x in the function call
Next steps: other ways to learn R
I got totally overwhelmed with the rate of new concepts in this class, or perhaps the pace and style of delivery. I think, given the time I have to spend after each class going over the material in order to make sense of it, it is clear that this course is not right for me. I have decided to abandon it and follow other materials more appropriate to my purpose, which is to develop skills in data visualisation using R. Despite the title, this course is not doing that for me.
Having decided2 to seek out other ways to learn how to R, I found that there are lots of self-directed learning resources out there, of course. An introduction to R course at DataCamp will be the new direction of travel down this rabbit hole for me.
Notes and references
I seem to be not the only one amongst the diminishing cohort (we’re down to a dozen today (Monday), having started closer to 50) that is finding it hard to follow this course. Yes, it’s interesting and cool, the different things you can do with R and geometries, but I am missing clarity, signposting, structure and other basic pedagogical features. ↩
Taking time after class 5 to review the presentation slides, it was possible to reconstruct perhaps what the instructor was intending, for example, in the two slides on probability and more generally with this class today. I might have got very little from today’s session without spending as long again going over the materials. I am perhaps going to seek out other resources. ↩