Reading the data 

• Download the D2K simulated ALSPAC dataset. 

• Read the data dictionary for this simulated dataset to familiarise yourself with the variables. 

• start a new script and save it as a .R file in an appropriate location
• comment in some header information: what is the script for? who is it written by? what data set is being used? etc
• set the working directory using setwd and read the dataset into R and assign it the variable sim.alspac using the read.csv function
• look up the colnames function in the help file and apply it to sim.alspac to list all the column headings in the data.
• look up the dim function in the help file and apply it to to sim.alspac to get the dimensions of the dataset.  Number of columns is the number of variables, number of rows is the number of participants. 

Selecting and subsetting

Selecting variables can be done a number of ways including selection by column number or column name.  It is best practice to use the column name as the column number may vary between datasets.

select.1<-dataframe[,x] #assign the variable select1 column number x in dataframe
select.2<-dataframe[,"x"] #assign the variable select2 column named x in dataframe
select.3<-dataframe$x #assign the variable select3 dataframe column x 

It is also possible to use operators to subset between a range of values.  See the help file for the subset function for further explanation

subset.4<-subset(dataframe, x < 5) #subset of the whole dataframe where x < 5
subset.4<-subset(dataframe, x == 5) #subset of the whole dataframe where x = 5

• create a subset of sim.alspac for males called subset.male and for females called subset.female
• How many participants are female and how many are male? HINT: Use dim to check the dimensions of subset.male and subset.female.  

Exploring the data

• Get object summary statistics by using the summary function on subset.male and subset.female
• Use the boxplot function to plot BMI at age 7 against gender. HINT: You will only need to use the arguments formula= and data=
• Use the hist function to plot histograms of BMI age 7 for females and males.  HINT: You can layer graphs over one another by using the argument add=T in the second histogram.  Line colour of the histogram can be set using the argument e.g. border="red"
• Make the plot more readable by using the legend to add an appropriate key.
• Output your graph as a .png file using the png function. 

Modelling

Rounding numbers

signif(x, digits = 6)

# set how many significant figures using digits =

or use

format(round(x, 2), nsmall = 2)

# for two d.p

Adding text to graphs

text(70,12, labels=paste("y=", RegM11$coefficients[2], "+", RegM11$coefficients[1]), col="orange")