As we did not have exact salaries, we used income ranges instead. However, as we could not graph ranges on excel, we used exact numbers in place of ranges. For example, instead of 0 to $20000, we used $10000 per year; instead of $20000 to $40000, we used $30000, and so on. Then we divided those numbers by 12 for the monthly income. We then calculated their actual monthly spending from the percentages with these calculated incomes. Then we made a scatter plot using salary as the explanatory variable and spending as the response variable. We set a trend line and found that linear gave the best fit. Calculation and r-squared values were also found through excel. We used data analysis: regression on data for 2009 for the values we used in the discussion.
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We hypothesized that expenditure on food necessities would not significantly change due to the economic recession, so we expect that the graphs for both years would have similar shapes. Both graphs show a slope of approximately 0.2, which indicates that the rate of food expenditure increases more slowly than the rate at which income increases. We noticed an increase in slope of 0.0017 between years, but we consider this change negligible. What is more significant is the translation of the graph for food expenditure in 2007 up the y-axis. This indicates that monthly expenditure on food has increased by $50 in 2009, which we believe to be a significant change because this represents a larger proportion of income spent on food.
