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The scale on the first plot is a bit disingenuous. Here's the same data replotted with a proper scale (i.e. ranging from 0 to 4 instead of 2.6 to 3.4). http://

The scale on the first plot is a bit disingenuous. Here's the same data replotted with a proper scale (i.e. ranging from 0 to 4 instead of 2.6 to 3.4). http://i.imgur.com/HxKss12.png http://i.imgur.com/HxKss12.png

Drakim 11y ago
"there are lies, damned lies and statistics" Your graph still shows the trend. But in a way, that's the most dangerous lie, the sort where you "help truth along" a little bit, to be more compelling.
pervycreeper 11y ago
Considering that a "grade" is an artificial quantity which doesn't represent the "mass" of anything real, the given scale is appropriate. The axes are also labelled very prominently, so I'm not sure what kind of false impression you think a reader would get from the first graph but not the second.
- bnegreve 11y ago
  Grades are at least supposed to reflect the quality of the students who pass the tests with some level of linearity. If the author doesn't believe this is the case, s-he shouldn't use them in the first place, especially not to discuss grade inflation. The kind of false impression that at least I get when I look at this graph is that the grades were multiplied by a factor ~1.3 over the past 20 years when they were only multiplied by a factor 1.06. For anyone familiar with GPA, this is misleading.
  - pervycreeper 11y ago
    >the grades were multiplied by a factor ~1.3 The point is that a grade is an ordinal quantity (somewhat). You don't get anything useful from multiplying grades by any "factor". Anyone in danger of thinking otherwise should not blame the graph. Fast food articles such as "Top 10 secrets of misleading graphs your profs don't want you to know" are probably more culpable in that regard.
    - bnegreve 11y ago
      > The point is that a grade is an ordinal quantity In principle I agree, but grade inflation preserves the order so why should we care about grade inflation if grades are only about order? I think the plot and the rest of the article goes beyond that. Also an histogram is a poor representation choice for ordinal data.
      - bryondowd 11y ago
        Grade inflation doesn't preserve order between the inflated and non-inflated grades, which I think is the point. An inflated low A might actually be lower than an original high B, but gets the shiny A that looks better on paper.
dalke 11y ago
What you likely want is the graph from the full paper, at http://www.gradeinflation.com/tcr2010grading.pdf http://www.gradeinflation.com/tcr2010grading.pdf .
deleted 11y ago
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hnnewguy 11y ago
>The scale on the first plot is a bit disingenuous It isn't really disingenuous. It's become fashionable to claim that "all graphs should start at zero", but that's not necessarily how you display data. Here is Edward Tufte: "In general, in a time-series, use a baseline that shows the data not the zero point. If the zero point reasonably occurs in plotting the data, fine. But don't spend a lot of empty vertical space trying to reach down to the zero point at the cost of hiding what is going on in the data line itself. (The book, How to Lie With Statistics, is wrong on this point.)" He's talking about time-series in this case, but the point remains: you need to understand the data. Sometimes (as in this case, where the trend is important, not the magnitude of change) showing the "zero" point is irrelevant.
- bnegreve 11y ago
  > It isn't really disingenuous. It's become fashionable to claim that "all graphs should start at zero", but that's not necessarily how you display data. Not all graphs no, but for histograms which are meant to compare quantities, maybe yes. See the other discussion in this thread. The kind of false impression that at least I get when I look at this graph is that the grades were multiplied by a factor ~1.3 over the past 20 years when they were only multiplied by a factor 1.06. For anyone familiar with GPA, this is misleading.

Drakim 11y ago

"there are lies, damned lies and statistics" Your graph still shows the trend. But in a way, that's the most dangerous lie, the sort where you "help truth along" a little bit, to be more compelling.

pervycreeper 11y ago

Considering that a "grade" is an artificial quantity which doesn't represent the "mass" of anything real, the given scale is appropriate. The axes are also labelled very prominently, so I'm not sure what kind of false impression you think a reader would get from the first graph but not the second.

bnegreve 11y ago
Grades are at least supposed to reflect the quality of the students who pass the tests with some level of linearity. If the author doesn't believe this is the case, s-he shouldn't use them in the first place, especially not to discuss grade inflation. The kind of false impression that at least I get when I look at this graph is that the grades were multiplied by a factor ~1.3 over the past 20 years when they were only multiplied by a factor 1.06. For anyone familiar with GPA, this is misleading.
- pervycreeper 11y ago
  >the grades were multiplied by a factor ~1.3 The point is that a grade is an ordinal quantity (somewhat). You don't get anything useful from multiplying grades by any "factor". Anyone in danger of thinking otherwise should not blame the graph. Fast food articles such as "Top 10 secrets of misleading graphs your profs don't want you to know" are probably more culpable in that regard.
  - bnegreve 11y ago
    > The point is that a grade is an ordinal quantity In principle I agree, but grade inflation preserves the order so why should we care about grade inflation if grades are only about order? I think the plot and the rest of the article goes beyond that. Also an histogram is a poor representation choice for ordinal data.
    - bryondowd 11y ago
      Grade inflation doesn't preserve order between the inflated and non-inflated grades, which I think is the point. An inflated low A might actually be lower than an original high B, but gets the shiny A that looks better on paper.

dalke 11y ago

What you likely want is the graph from the full paper, at http://www.gradeinflation.com/tcr2010grading.pdf http://www.gradeinflation.com/tcr2010grading.pdf .

deleted 11y ago

[deleted]

hnnewguy 11y ago

>The scale on the first plot is a bit disingenuous It isn't really disingenuous. It's become fashionable to claim that "all graphs should start at zero", but that's not necessarily how you display data. Here is Edward Tufte: "In general, in a time-series, use a baseline that shows the data not the zero point. If the zero point reasonably occurs in plotting the data, fine. But don't spend a lot of empty vertical space trying to reach down to the zero point at the cost of hiding what is going on in the data line itself. (The book, How to Lie With Statistics, is wrong on this point.)" He's talking about time-series in this case, but the point remains: you need to understand the data. Sometimes (as in this case, where the trend is important, not the magnitude of change) showing the "zero" point is irrelevant.

bnegreve 11y ago
> It isn't really disingenuous. It's become fashionable to claim that "all graphs should start at zero", but that's not necessarily how you display data. Not all graphs no, but for histograms which are meant to compare quantities, maybe yes. See the other discussion in this thread. The kind of false impression that at least I get when I look at this graph is that the grades were multiplied by a factor ~1.3 over the past 20 years when they were only multiplied by a factor 1.06. For anyone familiar with GPA, this is misleading.