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# AS and A Level: Probability & Statistics

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Meet our team of inspirational teachers Get help from 80+ teachers and hundreds of thousands of student written documents ## Statistical diagrams

1. 1 When working with grouped data, if the class is from 9 to 12, this includes values from 8.5 up to 12.5, which means the class width is 4, not 3.
2. 2 In a histogram, the area is the frequency. The y-axis is the frequency density.
3. 3 When working out lengths of scaled histograms, it is always helpful to draw the rectangle and label the relevant sides with the lengths given.
4. 4 When drawing a stem and leaf diagram, make sure to include a key. The key is worth a mark. For example 2|1 represents 2.1 or on a different stem and leaf, 3|2 represents 32.
5. 5 Always draw a scale when drawing a box plot, the scale is worth a mark.

## How to tackle questions on regression and correlation

1. 1 When asked about the relationship in a regression model, always get the context the correct way round. For example, weight does not affect height, height effects weight.
2. 2 When asked if your answer is reliable for the regression model, comment on whether the x value you used to get the answer is within the original data set. If the x value is within the boundary it is suitable. Never extrapolate when using a regression model.
3. 3 If you have found a regression model for a relationship between h and p, and are then told h=x+100 and p=y-20 and asked to find a regression model for x and y. Sub x+100 and y-20 into your original equation and re-arrange.
4. 4 When data is coded the correlation co-efficient is not changed.
5. 5 If a regression model is created using for example, heights and weights of children. This model could not be used to predict the weight of an adult. Models are very specific to the data with which they were created..

## Normal distribution

1. 1 When answering normal distribution questions always draw a picture and shade in the part of the graph that you know and/or want.
2. 2 In a normal distribution, the area under the curve represents the probability.
3. 3 A normal distribution model is appropriate if the mean and median are the same, or very close.
4. 4 The big normal distribution table gives area to the left of the line. The small table has areas to the right of the line.
5. 5 If unsure what the question is asking. Do the first step which is to rewrite the question, but converted to the normal distribution.

• Marked by Teachers essays 2
1.  ## The heights of 16-18 year old young adults varies between males and females. My prediction is that the majority of males are taller than females.

5 star(s)

So overall the data I collected wasn't bias and was accurate to use for my investigation. I decided to investigate the difference in heights between males and females ages 16-18 by collecting the data from students attending Havering Sixth Form College and then working out the Mean and Variance of both populations so that I could work out confidence intervals. To work out the mean and variance I had to illustrate tables for both populations. I drew up tables showing X as the height in inches which ranged from 60 - 73 in females and 62 - 76 in males.

• Word count: 2173
2.  ## data handling

3 star(s)

If any data is missing or obviously wrong, I will use another person instead. 11/261x50=2.1 I did that for all of the amounts. 14/261x50, 7/261x50 etc Months Boys Girls Total Amount Stratified amount for boys Stratified amount for girls September 11 9 20 2.11 1.72 October 14 6 20 2.68 1.15 November 7 13 20 1.34 2.49 December 9 17 26 1.72 3.26 January 13 6 19 2.49 1.15 February 17 10 27 3.26 1.92 March 15 17 32 2.87 3.26 April 9 8 17 1.72 1.53 May 9 11 20 1.72 2.11 June 12 13 25 2.3 2.49 July 9 16 25 1.72 3.07 August 4 6 10 0.77 1.15 129 132 261 24.71 25.29 Next I rounded up the numbers to their nearest whole number.

• Word count: 3869