Statistics - Part 2

Yesterday we spent some time looking at nominal, ordinal, interval and ratio levels of measurement. The key thing here is for you to be able to spot when the data is ordinal or only nominal.

We looked at the Wilcoxon Signed Ranks test - this is used to decide if scores in a repeated measures design experiment are significantly different. The data needs to be at least ordinal, because you have to rank the differences from smallest to largest, then add up the ranks of the positive differences and the ranks of the negative differences. If the smaller of these is less than the critical value (from the table) then the result is significant - in other words only a few results went 'the wrong way' and these only by a bit.

For Monday, make sure you have completed the Using the Sign Test sheet.

Also - gather some experimental data on open and closed passes. An open pass is when a person squeezes past someone else with their front to them - a closed pass is when they put their back to the other person. Create a tally chart for male and female passes and record the number of open and closed ones you observe for each.

Also have a go at the Mann-Witney U Test on the three-page sheet (on which you completed the Sign Test and Wilcoxon). The tricky bit here is that you have to rank the actual scores (NOT the differences between the scores - as this is and independent groups design the scores aren't actually in pairs), and you have to do this AS ONE GROUP meaning that you should get up to 20.