APA Style

There's no magic number for how many times you should have an in-text citation.  The general rule is that each time you use an idea or words from someone else you should provide a citation. This could mean having multiple citations in one sentence or having one citation at the end of entire paragraph.  Make sure that you cite in a way that someone reading your paper for the first time can match exactly which idea came from which source.

For an example of what NOT to do:

Frogs are excellent indicator species to measure wetland health. They are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. When frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. In addition, when oddities in frog morphology appear, like frogs with five legs or two heads, one can also assume something is going wrong in the wetland environment (Willemssen, 2010).

This writer has not included enough citations.  It's difficult to tell which part of this paragraph came from the source.

Here are two examples of GOOD in-text citation style:

Sample 1

Frogs are excellent indicator species to measure wetland health. According to a recent study by Willemssen (2010), frogs are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. The study notes that when frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. In addition, when oddities in frog morphology appear, like frogs with five legs or two heads, one can also assume something is going wrong in the wetland environment (Willemssen, 2010).

Sample 2

Frogs are excellent indicator species to measure wetland health.  Willemssen (2010) recently conducted research in Wisconsin that shows that frogs are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. Willemssen's research indicates that when frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. One very telling quote from Willemssen's research is that "87% of wetlands where two-headed frogs are found have high levels of  environmental contamination" (p. 341). 

Adapted from http://rasmussen.libanswers.com/faq/32328

Also known as an indirect or secondary citation.  The best way to handle this is to try and access the original source. For example, if you read a textbook that cites a medical study, you should try to find the medical study and cite directly from that. This can also be helpful to make sure you understand the context of the original study. The library offers a free Interlibrary Loan (ILL) service for both books and articles that the SFC Library does not have.

Sometimes however, you may not have access to the original source.  In that case cite the secondary source using "as cited in" in the in-text citation and mention the original source within the sentence. 

According to Blum, women metabolize more glucose and appear to use more of their brains on a given task (as cited in Rathus, 2008, p. 49).​

In the above example, Blum is the original source and Rathus is the secondary source.

In your reference list only include the works that you actually read and referenced in your essay (In the example above, you would include Rathus but not Blum).

eBooks are cited simliar to print books. It is not necessary to include the ebook format. If the book has a DOI or non-database URL this should be included too.

Example from an academic database:

Winters, A. (2014). The displaced of capital. University of Chicago Press.

Example with DOI or non-database URL:

Brown, L.S. (2018). Feminist therapy (2nd ed.). American Psychological Association. https://doi.org/10.1037/0000092-000

Since the page number of ebooks are not consistent (i.e. they change depending on the device and font settings) you should not use page numbers for in-text citations.  One option is to use paragraph numbers if they are provided. (You can also manually count the paragraphs if you wish.)

Winters describes the a summer thunderstorm noting how "the first drops strike their light civic stripes on the pavement" (para. 2).

It is okay to use page numbers in a pdf version of an ebook where the page numbers are consistent with the print version.