PPDAC Cycle

What is the PPDAC cycle? The PPDAC cycle is a way of answering statistics questions. Each letter stands for one step. P = D = A = C = Problem Plan Data Analysis Conclusions / Comments

Problem To use the PPDAC cycle you need to state a problem or question. A suitable investigative question needs: to be answerable with the data obtained, the population of interest to be clear, the variables to be clear, and the intention (summary or comparison) to be clear.

Examples of summary questions. I wonder what are the typical heights of Year12 students at HGHS in 2013. I wonder what are the typical number of people in the house for Year12 students at HGHS in 2013. Examples of comparison questions. I wonder if Year 12 students at HGHS in 2013 tend to have a larger neck circumference than Year 10 students at HGHS in 2013.

Plan You need to show a clear explanation of why the particular sampling method has been chosen The sampling method chosen must be one of the known sampling methods e.g. simple random, systematic, stratified and an explanation of why this sampling method was chosen.

For example: I have chosen to take a simple random sample For example: I have chosen to take a simple random sample. I have taken my random sample by drawing cards out of a bag. This method will provide me with a sample of heights where every Year 12 student at this school had an equal chance of being selected. The sample should therefore be representative of all the Year12 students at this school.

Data Relevant data must be directly related to the problem formulated. For a summary question the sample size should be at least 30. For a comparison question each sub group (or population) would need a sample size of at least 30.

For example: The student has listed the 30 students they selected from all the Year12 students. They have included all of the variables available.

Analysis Draw dot plots of the data. Draw box and whisker graphs to compare groups. Use SSUMO to analyse the graphs.

First draw a dot plot to give a very simple overview of the data First draw a dot plot to give a very simple overview of the data. From this graph features such as the shape or distribution of the data can be described. Also comments about spread, the middle group (or groups) and anything unusual can be noted. A box plot visually gives more information especially in comparison situations. The box plot gives a good indication of the range, the inter-quartile range and where the middle 50% (box) of the data lies. It is recommended that the associated dot plot is kept with the box plot.

Conclusions / Comments A conclusion to the problem should be related to the problem statement. In the conclusion you should have; the variable of interest values of the variable(s) with units as appropriate the population of interest.

e.g. Based on these data it seems that Year 10 boys were on average taller than the Year 10 girls. The median height and mean height for the boys was 170 cm compared with the median height and mean height for girls of 164 cm. This suggests that boys are on average about 6 cm taller than girls in Grade 10. There is a small amount of overlap between the middle 50% of height values. This small overlap supports the conclusion that boys are on average taller than girls. Also 75% of the boys are taller than 50% of the girls.