# Descriptive Statistics Part 1 – CEntral Tendency & Dispersion

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#### Learning Objectives

• To KNOW and UNDERSTAND what the term descriptive statistics means.
• To KNOW and UNDERSTAND what central tendency and a mean, median and mode is.
• To KNOW and UNDERSTAND what dispersion and a range, and standard deviation is
• To APPLY this knowledge  of descriptive statistics to the grass head project.
• To ANALYSE the types of central tendency in order to EVALUATE when to use them

### Lesson Outline:

1. To take notes in booklet, on the definition of quantitative data, qualitative data, primary data and secondary data.
2. To take notes in booklet, on the definition of descriptive statistics.
3. To take notes in booklet, on the definition of central tendency.
4. To use the data sets given and calculate the mean, median and mode for each.
5. To use the data sets given and your experience of completing the mean, median and mode for each data set to reflect on their strengths and limitations.
6. To take notes in booklet, on the strengths and limitations of mean, median and mode using the stems of ease, appropriateness, power and sensitivity.
7. To take notes in booklet, on the definition of dispersion.
8. To take notes in booklet, on the strengths and limitations of range and standard deviations using the stems of ease, appropriateness, power and sensitivity

#### Content Recap:

Qualitative Data: Qualitative data are those which are concerned with describing meaning, rather than with drawing statistical inferences. What qualitative methods lose on reliability they gain in terms of validity. They provide a more in depth and rich description.

Quantitative Data: Quantitative data are those that focus on numbers and frequencies rather than on meaning and experience. Quantitative methods provide information that is easy to analyse statistically and is fairly reliable. Quantitative methods are associated with the scientific and experimental approach and are criticised for not providing an in depth description

Primary Data : Primary data are gathered first hand from source, directly by the researcher(s).

Secondary data: Secondary data have already been gathered by someone and are used by someone else for further research.

Descriptive Statistics: Descriptive statistics quantitatively describe the main features of a collection of data. Descriptive statistics aim to provide a summary or overview of a data set.

Central Tendency: Central tendency relates to the way in which quantitative data is clustered around some value. A measure of central tendency is a way of specifying a central value. In the simplest cases, the measure of central tendency is an average of a set of measurements.

Mean: This is calculated by taking the sum of all scores and the dividing this by the number of scores.  It is a powerful method which is first choice for measures of central tendency except it is not always appropriate as it cannot be calculated for all types of data (nominal) and is easily skewed by outliers.

Median: This is calculated by taking the middle score when all scores have been ordered from the smallest to largest. It is used when there are outliers as it is unaffected but this is due to its lack of power, as all data is not used and again it is not always appropriate as it cannot be used for nominal data.

Mode: This is calculated by taking the most frequently occurring score or scores from the set of scores.  Whilst it is the least powerful it is the only choice for nominal data and can be good if there is a clear modal value.  It is less useful when there are bimodal results, or, indeed, no modal value.

Dispersion: How spread out (or diverse) the data is. It tells us whether there was a lot of variation or if the results were consistent. In psychological terms, was there individual differences

Range: This is calculated by subtracting the smallest number in a set of scores from the largest number in the same set. An easy method but effected by outliers.

Standard Deviation: This is calculated by taking the average that score deviates from the mean in a set of scores (although you will not be asked to calculate this one).

If you would like to access PsychoPepper’s Glossary of Terms please click here

#### Resources Used:

Central tendency Data Sets

#### Study Notes (TBC):

If you would like to download a set of study notes for this lesson, you can do so here.  If you would like access to the original word file please tweet @psychopepper

#### TEXTBOOKS OR EXTRA READING:

I would suggest that you have a copy of one of the textbooks which will allow you to read around the subject matter, pre-read ahead of lessons or even take extra notes/practise questions afterwards.  I would recommend the following (you do not need to replicate books, one of each type is plenty!)

Extra ReadingElephants on Acid or Hippo Eats Dwarf