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A bad data point: A scientist sampled data for a natural phenomenon that she has good reason to believe is appropriately modeled by an exponential function \(N=N(t)\). A laboratory assistant reported that there may have been an error in recording one of the data points but is not certain which one. Which is the suspect data point? Explain your reasoning. $$ \begin{array}{|c|c|c|c|} \hline t & N & t & N \\ \hline 0 & 21.3 & 4 & 204.4 \\ \hline 1 & 37.5 & 5 & 359.7 \\ \hline 2 & 66.0 & 6 & 633.1 \\ \hline 3 & 95.3 & & \\ \hline \end{array} $$

Short Answer

Expert verified
The suspect data point is at \( t = 4 \) with \( N = 204.4 \).

Step by step solution

01

Understanding Exponential Functions

An exponential function has the general form \( N(t) = a \, e^{kt} \), where \( a \) is the initial amount when \( t = 0 \), and \( k \) is the growth rate. In this case, the scientist expects the data to follow such a function.
02

Examining the Initial Data

Consider the data point at \( t = 0 \), where \( N = 21.3 \). This value represents \( a \) in the exponential function.
03

Calculating the Factor Between Consecutive Points

Calculate the ratio of \( N(t+1) \) to \( N(t) \) for the consecutive points to determine the factor by which the data points increase. For example, from \( t = 0 \) to \( t = 1 \), the factor is \( \frac{37.5}{21.3} \approx 1.76 \). Repeat for other consecutive pairs.
04

Identifying Inconsistencies

After calculating all the ratios, identify if any data points have a significantly different ratio. The general trend should show consistent growth factors. Look for outliers.
05

Evaluating the Deviating Data Point

The data point from \( t = 3 \) to \( t = 4 \) has a factor of \( \frac{204.4}{95.3} \approx 2.14 \), which is noticeably higher than the other growth factors, suggesting that this data point is inconsistent with the exponential growth pattern.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Data Analysis
Analyzing data often requires us to search for patterns or trends within a dataset. When we have a series of data points, our task is to understand how these points relate to each other over time or another variable, like in the case of our exercise. This requires a careful examination of the values given and finding a suitable model to fit the expected pattern.

For instance, if we assume that a particular phenomenon should follow an exponential growth model, as the scientist does, we anticipate the data to increase by a fairly predictable factor. This expected growth pattern is what helps analysts to catch anomalies or errors in the data.

By calculating the growth factor between consecutive data points, analysts can confirm whether the pattern holds consistently. If all factors remain similar but one diverges significantly, it signals that something may be amiss with that particular data point. Thus, effective data analysis involves both understanding the expected structure (such as exponential growth) and verifying that the actual data adheres to it through calculation and comparison.
Exponential Growth
Exponential growth is characterized by the property that the rate of change of a quantity is proportional to the quantity itself. In mathematical terms, if a phenomenon follows exponential growth, its equation is generally written as \[ N(t) = a \, e^{kt} \] where \( a \) is the initial amount and \( k \) is the growth rate constant.

One captivating feature of this growth type is its rapid increase over time. Unlike linear growth, which adds a constant amount in each step, exponential growth multiplies by a constant factor. This means each subsequent value is larger due to being a product of the previous quantity multiplied by this consistent factor.

In our data values, we observed growth such as from \( t = 0 \) to \( t = 1 \), the factor was approx 1.76. Ideally, for exponential growth, succeeding factors should remain close to each other, barring errors or exceptions. For every choice of \( t \), confirming the adherence to this powerful pattern is central to verifying the presence of exponential growth.
Error Detection
Detecting errors in data requires keen observation and a methodical approach. Particularly with exponential data, seeking outlier points that deviate from the predicted pattern is crucial. Once a suitable model like exponential growth is assumed, it dictates that deviations from the model's expected behavior can highlight inaccuracies.

Conducting ratio calculations between successive data points can reveal inconsistencies. In our example, the data point transitioning from \( t = 3 \) to \( t = 4 \) was flagged as suspicious due to a growth factor \( \approx 2.14 \), notably higher than previous computations.

This deviation is critical because constant growth ratios support our exponential model hypothesis. By identifying the considerably differing factor, it allows us to pinpoint the potential error. This systematic approach not only helps maintain the integrity of the data but also ensures that resulting conclusions drawn from the dataset are reliable and accurate.

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Most popular questions from this chapter

Stand density: Forest managers are interested in measures of how crowded a given forest stand is. \({ }^{33}\) One measurement used is the stand-density index, or \(S D I\). It can be related to the number \(N\) of trees per acre and the diameter \(D\), in inches, of a tree of average size (in terms of cross- sectional area at breast height) for the stand. The relation is $$ \log S D I=\log N+1.605 \log D-1.605 . $$ b. What is the effect on the stand-density index of increasing the number of trees per acre by a factor of 10 , assuming that the average size of a tree remains the same? c. What is the relationship between the stand-density index and the number of trees per acre if the diameter of a tree of average size is 10 inches? a. A stand has 500 trees per acre, and the diameter of a tree of average size is 7 inches. What is the stand-density index? (Round your answer to the nearest whole number.) b. What is the effect on the stand-density index of increasing the number of trees per acre by a factor of 10, assuming that the average size of a tree remains the same? c. What is the relationship between the stand-density index and the number of trees per acre if the diameter of a tree of average size is 10 inches?

Age of haddock: The age \(T\), in years, of a haddock can be thought of as a function of its length \(L\), in centimeters. One common model uses the natural logarithm: $$ T=19-5 \ln (53-L) $$ a. Draw a graph of age versus length. Include lengths between 25 and 50 centimeters. b. Express using functional notation the age of a haddock that is 35 centimeters long, and then calculate that value. c. How long is a haddock that is 10 years old?

The pH scale: Acidity of a solution is determined by the concentration \(H\) of hydrogen ions in the solution (measured in moles per liter of solution). Chemists use the negative of the logarithm of the concentration of hydrogen ions to define the \(\mathrm{pH}\) scale: $$ \mathrm{pH}=-\log H . $$ Lower pH values indicate a more acidic solution. a. Normal rain has a pH value of 5.6. Rain in the eastern United States often has a pH level of \(3.8\). How much more acidic is this than normal rain? b. If the \(\mathrm{pH}\) of water in a lake falls below a value of 5 , fish often fail to reproduce. How much more acidic is this than normal water with a \(\mathrm{pH}\) of \(5.6 ?\)

Magnitude and distance: Astronomers measure brightness of stars using both the absolute magnitude, a measure of the true brightness of the star, and the apparent magnitude, a measure of the brightness of a star as it appears from Earth.42 The difference between apparent and absolute magnitude should yield information about the distance to the star. The table on the following page gives magnitude difference m and distance d, measured in light-years, for several stars. a. Plot ln d against m and determine whether it is reasonable to model distance as an exponential function of magnitude difference. b. Give an exponential model for the data using the logarithm as a link.$$ \begin{array}{|l|c|c|} \hline \text { Star } & \begin{array}{c} \text { Magnitude } \\ \text { difference } m \end{array} & \text { Distance } d \\ \hline \text { Algol } & 2.56 & 105 \\ \hline \text { Aldebaran } & 1.56 & 68 \\ \hline \text { Capella } & 0.66 & 45 \\ \hline \text { Canopus } & 2.38 & 98 \\ \hline \text { Pollux } & 0.13 & 35 \\ \hline \text { Regulus } & 2.05 & 84 \\ \hline \end{array} $$ c. If one star shows a magnitude difference 1 greater than the magnitude difference that a second star shows, how do their distances from Earth compare? d. Alphecca shows a magnitude difference of 1.83. How far is Alphecca from Earth? e. Alderamin is 52 light-years from Earth and has an apparent magnitude of 2.47. Find the absolute magnitude of Alderamin.

Growth in length of haddock: A study by Riatt showed that the maximum length a haddock could be expected to grow is about 53 centimeters. Let D = D(t) denote the difference between 53 centimeters and the length at age t years. The table below gives experimentally collected values for D. $$ \begin{array}{|c|c|} \hline \text { Age } t & \text { Difference } D \\ \hline 2 & 28.2 \\ \hline 5 & 16.1 \\ \hline 7 & 9.5 \\ \hline 13 & 3.3 \\ \hline 19 & 1.0 \\ \hline \end{array} $$ a. Find an exponential model of \(D\) as a function of \(t\). b. Let \(L=L(t)\) denote the length in centimeters of a haddock at age \(t\) years. Find a model for \(L\) as a function of \(t\). c. Plot the graph of the experimentally gathered data for the length \(L\) at ages \(2,5,7,13\), and 19 years along with the graph of the model you made for \(L\). Does this graph show that the 5 year-old haddock is a bit shorter or a bit longer than would be expected? d. A fisherman has caught a haddock that measures 41 centimeters. What is the approximate age of the haddock?

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