Cheat Sheet
Statistics Workbook For Dummies Cheat Sheet
Statistics is all about interpreting numbers, which is where Ztables and ttables come in handy as they help you determine distribution numbers and confidence levels. And, when it comes to statistics tests, tips like reading the whole question before doing any figuring can save you time and improve your score.
Statistical Standard Scores and Standard Normal Distributions — The “ZTable”
Statistics are handy when it comes to making predictions, but to make accurate predictions, you need to know how reliable your results are. The following Z table shows standard scores and percentiles in a standard distribution:
Standard Score  Percentile  Standard Score  Percentile  Standard Score  Percentile 

–3.4  0.03%  –1.1  13.57%  +1.2  88.49% 
–3.3  0.05%  –1.0  15.87%  +1.3  90.32% 
–3.2  0.07%  –0.9  18.41%  +1.4  91.92% 
–3.1  0.10%  –0.8  21.19%  +1.5  93.32% 
–3.0  0.13%  –0.7  24.20%  +1.6  94.52% 
–2.9  0.19%  –0.6  27.42%  +1.7  95.54% 
–2.8  0.26%  –0.5  30.85%  +1.8  96.41% 
–2.7  0.35%  –0.4  34.46%  +1.9  97.13% 
–2.6  0.47%  –0.3  38.21%  +2.0  97.73% 
–2.5  0.62%  –0.2  42.07%  +2.1  98.21% 
–2.4  0.82%  –0.1  46.02%  +2.2  98.61% 
–2.3  1.07%  0.0  50.00%  +2.3  98.93% 
–2.2  1.39%  +0.1  53.98%  +2.4  99.18% 
–2.1  1.79%  +0.2  57.93%  +2.5  99.38% 
–2.0  2.27%  +0.3  61.79%  +2.6  99.53% 
–1.9  2.87%  +0.4  65.54%  +2.7  99.65% 
–1.8  3.59%  +0.5  69.15%  +2.8  99.74% 
–1.7  4.46%  +0.6  72.58%  +2.9  99.81% 
–1.6  5.48%  +0.7  75.80%  +3.0  99.87% 
–1.5  6.68%  +0.8  78.81%  +3.1  99.90% 
–1.4  8.08%  +0.9  81.59%  +3.2  99.93% 
–1.3  9.68%  +1.0  84.13%  +3.3  99.95% 
–1.2  11.51%  +1.1  86.43%  +3.4  99.97% 
Tips for Statistics Test Success
Working on statistics problems (especially word problems) can be frustrating; but it doesn’t have to be! You just have to avoid the urge to jump right in and start doing calculations because the key to success is to develop a sound strategy. Use the following tips for test success (other students have found them helpful):

Think about what the problem is asking you to do (this is often stated in the last sentence of the problem).

Come up with a list of keywords that identify each different technique, and look for them in the problems, so you’ll know how to attack those problems on an exam.

Write down the formula you plan to use and label which numbers you want to plug in to each piece.

Do the calculations correctly and document your work.

Check your answer to see if it makes sense.

Interpret the results correctly, giving both the “statistically correct” answer (I’m 95 percent confident that the population mean is 16 inches, plus or minus 1 inch”) and the “answer in the context of the problem” (“This means we are 95 percent confident that the average height of this breed of dog is between 15 and 17 inches”).
Statistical TDistribution — The “TTable”
As a statistical tool, a ttable lists critical values for twotailed tests. You then use these values to determine confidence values. The following ttable shows degrees of freedom for selected percentiles from the 90th to the 99th:
Degrees of Freedom  90th Percentile (a = .10)  95th Percentile (a = .05)  97.5th Percentile (a = .025)  98th Percentile (a = .02)  99th Percentile (a = .01) 

1  3.078  6.314  12.706  31.821  63.657 
2  1.886  2.920  4.303  6.965  9.925 
3  1.638  2.353  3.182  4.541  5.841 
4  1.333  2.132  2.776  3.747  4.604 
5  1.476  2.015  2.571  3.365  4.032 
6  1.440  1.943  2.447  3.143  3.707 
7  1.415  1.895  2.365  2.998  3.499 
8  1.397  1.860  2.306  2.896  3.355 
9  1.383  1.833  2.262  2.821  3.250 
10  1.372  1.812  2.228  2.764  3.169 
11  1.363  1.796  2.201  2.718  3.106 
12  1.356  1.782  2.179  2.681  3.055 
13  1.350  1.771  2.160  2.650  3.012 
14  1.345  1.761  2.145  2.624  2.977 
15  1.341  1.753  2.131  2.602  2.947 
16  1.337  1.746  2.120  2.583  2.921 
17  1.333  1.740  2.110  2.567  2.989 
18  1.330  1.734  2.101  2.552  2.878 
19  1.328  1.729  2.093  2.539  2.861 
20  1.325  1.725  2.086  2.528  2.845 
21  1.323  1.721  2.080  2.518  2.831 
22  1.321  1.717  2.074  2.508  2.819 
23  1.319  1.714  2.069  2.500  2.807 
24  1.318  1.711  2.064  2.492  2.797 
25  1.316  1.708  2.060  2.485  2.787 
26  1.315  1.706  2.056  2.479  2.779 
27  1.314  1.703  2.052  2.473  2.771 
28  1.313  1.701  2.048  2.467  2.763 
29  1.311  1.699  2.045  2.462  2.756 
30  1.310  1.697  2.042  2.457  2.750 
40  1.303  1.684  2.021  2.423  2.704 
60  1.296  1.671  2.000  2.390  2.660 
Zvalues  1.282  1.645  1.960  2.326  2.576 