Session 4: Scatterplots and Correlations

Making a Scatterplot

A scatterplot gives a visual picture of the relationship of (usually)
two continuous variables. One can also use Likert-scaled variables in
a scatterplot. Pick two variables that can be seen as an explanatory
(independent) variable and a response (dependent) variable. Draw a
scatterplot (
Graphs/Legacy Dialogs/Scatter/Simple Scatter

) so that the
dependent variable goes to the Y axis and the independent variable
goes to the X axis. Interpret the resulting scatterplot.

Add a regression line to the finished figure by first entering the chart editor by double clicking the chart, and then selecting the
plots in the figure by clicking them and selecting
Chart/Add Chart Element/Fit Line at Total/Fit Method: Linear

. What conclusions you can draw from the scatterplot?

Computing Correlations

If it appears that there is a linear dependency between your chosen
variables, compute the correlation between the variables

). What does the correlation
coefficient tell you? Is the correlation between the variables
statistically significant?

Correlation and Statistical Significance

Go back to (or redo) the correlation matrix made in day 3, and write a short
analysis on its correlation coefficients and their statistical significance.

Interpreting Correlation

Draw a scatterplot with a regression line and compute the correlation
coeffiecient for the
variables “Country’s cultural life undermined or enriched by immigrants”
(imueclt) and “Year of birth” (yrbrn). How do you interpret the correlation

Preparing Graphs and Tables for Reports

Pick a graph or a table you made before, and make it fit for
publishing. Use the following guidelines (adapted from Maarit

, especially for crosstabulations):

  • Only display row, column OR cell percentages in your tables, but
    don’t use the %-character. Usually there’s no need to display cell
  • Display the figures, where the percentages are counted from,
    i.e. row and column sums and their total sum. If the reader is
    interested in cell frequencies, he/she can count them utilizing the
    displayed percentages.
  • A good way to make sure that the percentages are displayed
    correctly is to attempt to explain the central conclusion of the
    table. An example from a study regarding reading as a hobby: “88% of
    adults in Narujärvi, and 32% of adults in Uppojoki read at least 3
    novels each year.” (It would be considerably more awkward to state the
    percentage of people reading novels coming from Uppojoki.)
  • Avoid displaying too much decimal numbers, they make your graphs
    less readable.
  • Display the sum of percentages, that is a row or column of 100s,
    either in the right or bottom marginal depending on the direction of
    the counted percentages.
  • The meaning of a variable’s categories must be explicated
    clearly. Usually the variable value (i.e. the category “number”) is
    not enough, but each category should have a description in the
    table. This is easily done by giving the variable value labels in the
    Variable View. If the category descriptions don’t fit in the table,
    further explications can be situated in the footnotes.
  • The table title should be informational, and additional
    descriptions can be written in the footnotes if needed.
    The reader
    should be able to understand the table’s contents without looking for
    explanations from the report’s text proper.

    The title does not
    need to be smart nor snappy, this being a scientific report. An
    example of a title: The distribution of Finnish women aged 18 to 35
    years in income categories in the year 1997.
  • The table source is written in the lower margin of the table.
  • Repeating the figures and details from the table excessively in
    the report’s text is a sure way of making the reader lose
  • A table needs to have a number in addition to a title.
  • When dealing with a table of percentages, the number of
    observations should be clearly displayed.
  • The best tip: Show your tables and graphs to a friend who’s not
    afraid to speak out, and ask her to tell you what the tables are
    about, and what conclusions one can make from the figures.

For information on how to tidy up the charts and graphs in your final report, consult these examples.