After reading the paragraphs below, answer the questions that follow.
A negative impact of biofilms in the human body is that biofilms can cause head and neck diseases. A study was completed that compared three groups of medical patients for presence or absence of biofilms. Group 1 were patients with chronic otitis media (COM), a disease where the eardrum continually drains and can often become clogged, that also displayed ear discharge. Group 2 were COM patients without ear discharge. Group 3 were patients undergoing surgery for cochlear implantation, a procedure where a small electronic instrument is placed in the ear to carry out normal functions of the inner ear. Two microscopy methods were used to detect presence of biofilms in all patients of both groups: direct microscopy (DM) and transmission electron microscopy (TEM).
The table below shows the results of presence or absence of biofilms in all study participants.
Table 1. Number of study participants detected with biofilms
| Group | Group Size | Biofilm on DM | Biofilm on TEM |
| 1 COM, discharge | 10 | 10 | 10 |
| 2 COM no discharge | 9 | 2 | 2 |
| 3 cochlear implant | 10 | 0 | 0 |
| Total | 29 | 12 | 12 |
Source: Adapted from Akyıldız, I., Take, G., Uygur, K., Kızıl, Y., & Aydil, U. (2013). Bacterial biofilm formation in the middle-ear mucosa of chronic otitis media patients.
Indian J Otolaryngol Head Neck Surg, 557-561. doi:10.1007/s12070-012-0513-x
Which group served as the control group in the experiment?
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