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A scientist was asked to test the effect of a new vitamin for rats. His hypothesis was that young rats that had vitamins added to their food would gain weight faster than young rats fed a normal diet. He predicted that if young rats were fed vitamins, then they would gain more weight by the end of the experiment. He tested the effect of adding vitamins to some of the rats' diet by measuring the amount of weight each rat gained after three months. He then determined the average weight gained in each group. To analyze his results, he put the data he collected into the table shown below.

\begin{tabular}{|c|c|c|c|c|c|c|c|}
\hline \multicolumn{4}{|c|}{ Rats fed normal diet } & \multicolumn{4}{|c|}{ Rats fed normal diet and vitamins } \\
\hline Rat \# & \begin{tabular}{l}
Starting \\
weight
\end{tabular} & \begin{tabular}{l}
Ending \\
weight
\end{tabular} & \begin{tabular}{l}
Difference \\
in weight
\end{tabular} & Rat \# & \begin{tabular}{l}
Starting \\
weight
\end{tabular} & \begin{tabular}{l}
Ending \\
weight
\end{tabular} & \begin{tabular}{l}
Difference \\
in weight
\end{tabular} \\
\hline 1 & 256 g & 320 g & 64 g & 1 & 249 g & 342 g & 93 g \\
\hline 2 & 274 g & 347 g & 73 g & 2 & 221 g & 307 g & 86 g \\
\hline 3 & 209 g & 268 g & 59 g & 3 & 278 g & 381 g & 103 g \\
\hline \begin{tabular}{l}
Average \\
weight \\
gain
\end{tabular} & & & 65 g & \begin{tabular}{l}
Average \\
weight \\
gain
\end{tabular} & & & 94 g \\
\hline
\end{tabular}

Which of the following could have added bias to the data?

A. Keeping the rats in the same room, but in separate cages during the experiment
B. Not using all male or all female rats, since they are different sizes when grown
C. Recording the data in a table instead of on a graph



Answer :

GinnyAnswer
To address the question of potential bias in the scientist’s experiment, we need to carefully consider each of the options provided:

### Option A: Keeping the rats in the same room, but in separate cages during the experiment
This option suggests that keeping the rats in the same room but in separate cages could introduce bias. However, provided the environmental conditions (such as light, temperature, and noise) are uniform across the room, separating the cages is a consistent method that could help minimize stress by reducing interaction between the rats. Therefore, this method is unlikely to introduce significant bias.

### Option B: Not using all male or all female rats, since they are different sizes when grown
This option highlights a significant potential source of bias. Male and female rats have different metabolic rates, growth patterns, and possibly react differently to dietary changes, including vitamin supplementation. Introducing both genders in the study can lead to variability in the results that is independent of the diet being tested. This means the differences in weight gain observed may partly be due to gender differences rather than the effect of the vitamins, thereby introducing bias.

### Option C: Recording the data in a table instead of on a graph
This option concerns the method of data presentation. Whether data is recorded in a table or on a graph is a matter of presentation and does not affect the data itself. Recording the data in a table is merely a method of organizing and displaying the data and does not introduce bias into the experimental results.

### Conclusion
Based on the analysis above, the most significant potential source of bias in the experiment is Option B: Not using all male or all female rats. This would introduce variability due to inherent differences between male and female rats, which are not related to the diet they received.

Therefore, the most likely source of bias in this experiment is:
B. Not using all male or all female rats, since they are different sizes when grown.

By ensuring all the rats used in the experiment are of the same gender, the scientist could better isolate the effect of the vitamin supplementation on weight gain.

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