The entire student population of the US has been divided into state/territories as different strata. Samples are then obtained from each stratum. The advantages of this technique are:
This structure and design of the frequency table was chosen because it makes it easier to analyze data using tools such as Microsoft Excel and SPSS. It is also simple to extract data from or to do cross tabulations. As you can see the measures of central tendency: mean, mode and median have been easily calculated using MS-Excel. The section in Table 1 written #N/A shows no mode / multimodal data.
From chart 2 we can conclude that Grade 12 students had the highest percentage mean of those who rarely or never wore a seat belt when riding in a car driven by someone else. This is different from Chart 3 below which shows us that Grade 9 had the highest percentage median of the same data. This implies that the data has extreme values.
From charts above and below looking at the samples for gender we see we have a skewed distribution. We can see long right-tails which implies positive skewness. A normal distribution is symmetric and has a skewness value of 0. The standard deviation is a measure of dispersion around the mean. In our case the standard deviation is very high when compared to the mean, 9.066 for Male data and 9.575 for Female data. This means that our data has a very wide spread from the centre.
a. Parameters are numbers that are used to describe characteristics of an entire population while statistics are numbers that describe characteristics derived from a sample that has been drawn from a larger population.
The standard deviation is a measure of dispersion around the mean. It is the positive square root of the variance. Range is the difference between the highest and lowest values in a sample or population. The inter-quartile range is got from the difference between the 3rd and 1st quartiles of the sample/population data.