Exam One

What range of volume does the micropipet deliver?

0.2 to 1000 µL

Where is the liquid in a micropipet held?

In the disposable polypropylene tip, stable for most aqueous solutions and many organic solvents except chloroform (CHCl₃)

What is the micropipet also not resistant to other than chloroform?

Concentrated nitric or sulfuric acids

How does a micropipet prevent aerosols from entering the pipet shaft and causingh corrosion or cross contamination?

Some tips have polyethylene filters

What is the difference between accuracy and percision?

Accuracy refers to how close a measured value is to the true value, while precision indicates the consistency of repeated measurements.

What is an example where a labeling error can result in a significant problem?

Consider a patient’s blood sample with a name labelling error

What is quantitative chemical analysis?

The measurement of how much of a chemical substance is present in a sample.

What is the purpose of quantitative chemical analysis?

To determine the concentration or amount of substances in a sample. Checking to see if there is a difference from the blank measure that is different from the random noise present.

i.e. “Does this mineral contain enough copper to be an economical source?” or “ Has there been a significant increase in the amount of SARS-COV-2 antibodies in this patients blood?”

What is a t-test?

A statistical test used to compare the means of two groups to determine if they are significantly different from each other.

What are some examples of tools for chemical analysis?

Micropipet, Beaker, and Graduated Cyclinder

Fill in the following statement:

Experimental error is present in ______ measurement.

every

True or False

There is no way to measure the “true” value?

True, because all measurements are subject to error.

What are some examples of different types of error?

Human error, Instrumental error, Labeling Error

What do Random/indeterminate errors affect?

The precision of the result.

i.e. Base line noise in a dopamine test

What does random error arise from?

Uncontrolled variables in measurement that have equal chance of being positive or negative and are always present, nor can be entirely eliminated.

What does systematic error deal with?

It affects the accuracy or nearness to the true value.

What does systematic error arise from?

Flaws in equipment or in the experimental design, which are reproducible and can often be corrected.

How do we deal with experimental error?

With care in experimental design, calibration, and repeated trials to minimize its impact. Random errors however are always present so mathematical methods such as propagation rules help to minimize their effects by accounting for the error in the results.

What is an example of how we account for random error?

Signal averaging or lock-in detectors.

What is Gaussian Distribution?

A statistical distribution characterized by its bell-shaped curve, where most values cluster around the mean, and probabilities for values further away from the mean taper off symmetrically.

What is the symbol for the mean in Gaussian distribution?

x̄, the average and center of distribution

What is the symbol for standard deviation in Gaussian distribution?

s, measures how closely the data clusters about the mean, and the width of the distribution

In ideal gaussian distribution, where does the maximum x occur?

At the mean value. (µ)

True or False:

The probability of observing a value within a certain interval is proportional to the area of that interval.

Treu

What is the F-test?

A statistical test used to compare the variances of two populations to determine if they are significantly different.

What is the formula for an F-test?

F = (s1² / s2²), where s1² and s2² are the sample variances of the two populations being compared.

From a limited number of measurements (n),. we cannot find the true population mean, µ, or the true standard deviation, ∂. What can we determine?

The x and s or the sample mean and the sample standard deviation.

What does the confidence interval allow us to state?

At some level of confidence, a range of values that include the true population mean.

Why is a low level of confidence in a confidence interval result in a smaller confidence interval?

Because a lower confidence level means we are willing to accept a higher margin of error, thus narrowing the range of values around the sample mean.

When data sets are compared in a study what does p mean?

The p-value indicates the probability of observing the data, or something more extreme, given that the null hypothesis is true.

The world population at any given time is off by upwards of 2-3% regardless of the method used to count. What does this represent?

The fact that any measurement has some kind of error.

Since experiment measurements will always contain variability whtat cn not be done.

A conclusion can not be drawn with absolute certainty.

What do statistical tools allow us to do?

To accept or deny conclusions which have high (or low) probability of being correct.

For simple gaussian distribution how do you calculate the degrees of freedom?

n-1

What is variance in Gaussian distribution?

A measure of the dispersion of a set of values in a Gaussian distribution, calculated as the average of the squared differences from the mean.

How do you calculate relative standard deviation?

.

How do we calculate percent relative standard deviation?

.

What do we use when the mean values of two sets of measurements are statistically different from each other when experimental uncertainty is considered?

The t-test, which compares the means of two groups to determine if they are statistically different.

What is the null hypothesis?

Data sets A and B are not significantly different.

When can we reject the null hypthesis?

When the chance of it being true is < 5% (95% confidence)

If t_calc < t_{table, 95%} the null hypothesis is confirmed when?

p>0.05, data is statistically equal

If t_calc > t_{table, 95%} the null hypothesis is rejected when?

p < 0.05, data is statistically different.

What is the meaning of not significantly different?

We are 95% confident that the data sets are equal.

What about a p < 0.001?

We are 99.9% confident that the data sets are different.

What is the prupose of the Grubbs test?

The Grubbs test is used to detect outliers in a univariate data set, helping to determine if a single data point is significantly different from the rest of the data.

What is the formula of the Grubbs test?

G = max |xi - x̄| / s, where xi is a data point, x̄ is the mean of the data set, and s is the standard deviation.

What is the point of the calculations of the mean and standard deviation?

Even with limited data we can make an educated guess about the distribution of the future measurments.

If we expanded aa data set to 1000 measurements what would the histogram look like?

Gaussian distibution, and we only need the mean and standard deviation to do it.

Finish the Statement:

If n increase then the prediction ________.

Changes as the values approach true distribution

When do we know if a line is a good fit with a least squares regression line?

With a R² > 0.99

For significant figures, what do you always round standard deviation to?

one significant figure

For significant figures what do you round the mean to?

the same decimal place as the data sets standard deviation.