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9 Cards in this Set
- Front
- Back
Compare accuracy and precision?
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Precision: Closeness of results that have been obtained in the same way
Accuracy: the closeness of the measurement to its true value or accepted value. -it can NEVER be exactly because true value is never exactly known. |
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What statistical calculations are used to determine precision?
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1. Standard deviation
2. Variance 3. Relative Standard Deviation (RSD) 4. Coefficient of Variance (CV) |
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What statistical calculations are used to determine accuracy?
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1. Absolute error = u - x
2. Relative error = (u - x)/u |
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What are the causes of systematic error?
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1.interference: e.g. due to sample itself, temp, etc
2. Sampling error: e.g. bubbles in pipets 3. Error in standards or control 4. Old/bad reagents 5.Wrong instrument setting 6. Electrical interference 7. Instrument design - doesn't do what it suppose to do. 8. Personal bias 9. chemical purity |
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What are the cause of random error?
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Causes: affecting one sample per run.
1. Sample collection 2. Sample preservation problem 3. Sample transport problem 4. Sample storage problem 5. Calculation error 6. Reporting results e.g., 1.0 --> 0.1 reported |
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List three measures of central tendency?
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Central tendency are statistics that represent some central value around which the data is distrubuted.
1.Mean 2. Median 3. Mode |
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How to find median for odd set?
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Odd set, n = total
1. order highest to lowest 2. n+1 3.divide by two 4.position = median value |
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How to find median for even set?
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Even set, n= total
1. order highest to lowest 2. n/3 3. +1 4. Median is average of (n/2) and (n/2 +1) |
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Describe the types of errors that exist in measurements.
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1. Systematic error (determinate)
-affect accuracy, assign cause, same magnitude 2. Random (indeterminate) -affect precision, no pattern, uncontrollable 3. Personal errors - mistakes, carelessness, inattention, and prejudice 4. Gross errors - Outliers |