<p>Hello, I am new here, but actually my first semester at WashU is close to an end now.</p>
<p>I have a question about the grading of general chemistry 111.</p>
<p>How to convert total quiz score into normalized score in a 100-scale? </p>
<p>eg. 65 in the quizzes = ? in a 100-scale
60 = ? </p>
<p>TA says that professors use cryptic formulas to make conversion, and rumor goes that the conversion is so cruel that it is generally impossible to replace exams with normalized quiz scores (unless one severely blows one exam)</p>
<p>From the chem website (I will not even begin to interpret)…</p>
<p>Exam scores will be scaled to a mean of 60 and a standard deviation of 15, by something called a “z-score.”</p>
<p>Here is how it’s done:</p>
<ol>
<li><p>For each exam, your “raw” test score (x), the mean for the entire class for that exam (xm), and the standard deviation (σ) are used to calculate your z-score:
z = (x – xm)/ σ
For example, the mean for Exam 1 was xm=55.31 and σ =14.01.</p></li>
<li><p>Your z-score is used to calculate your test score in this new distribution, a “scaled” test score, xsc. The new “scaled mean” (xscm) is 60 and the new standard deviation is 15 (σsc). These values will give a distribution of scores peaked at 60.</p></li>
<li><p>The formula is: xsc = (z * σsc) + xscm = (z * 15) + 60.
For example, if you scored one-σ below the mean, 55.31 – 14.01 = 41.30, it’ll now be
45=60-15 (i.e., one-σ below the mean).</p></li>
</ol>
<p>Take-home message: if your old score was one-σ away from the old mean of 55.31, it will still be one-σ away from the new mean of 60.</p>