What to include
Despite what you may read in non-academic writing, the only information you should include when citing research in-text is information about the study, the authors' last names, and the year. Popular press articles often include the name of the article, the name of the journal in which it was published, and even the institutions where the authors work, but none of this is included in academic writing. Academic writing is short, sweet, and to the point, so you should only include the important stuff, including important details of the study and the information that efficiently tells you how to find the original research (the authors' last names and the year).
In short, you need:
The authors' last names (not first names, initials, degrees, or anything other than their last names)
The year the article was published
Where to put the reference
You have a lot of freedom in how you want to cite in-text as long as you include all of the necessary information. If you cite the reference parenthetically (in parentheses at the end of the sentence), the format is more standardized. Below are a few examples of how you could format your citation:
In their study on adolescent peer relationships, Parkhurst and Hopmeyer (1998) identified two unique forms of popularity: sociometric and perceived popularity.
Myrick (2015) found that procrastination guilt decreases the enjoyment experienced while watching cat videos online.
A 2011 study by Lillard and Peterson tested the effects of different types of television on executive functioning in young children.
As opposed to childhood, when family was most central to the individual, adolescents are more likely to list peers among the most important people in their lives (Furman & Buhrmester, 1992).
You should always put the citation in the first sentence where you talk about that study. If multiple sentences (or more) all refer to the same paper, you only need to cite it at the beginning, and the reader will generally assume that you're still talking about the same thing. If the study has multiple points that are somewhat disconnected, you may want to cite the same paper two or more sentences in a row (e.g. one sentence is on rates of depression in girls, and the next sentence is on rates of ADHD in boys. They both came from the same source, but they may seem like they came from different studies). You want your reader to have an easy time knowing where to look for the reference. If you seem to be talking about something completely different, it's worth it to re-cite the paper just so your reader doesn't have to wonder where you're coming up with what you're saying, even if that means citing the same study two sentences in a row.
How to format it
The number of authors determines how the reference gets cited. Below are a couple examples for each. When putting the authors' names in parentheses, use "&" instead of "and" between the last two authors' names.
Myrick (2015) found that...
Lillard and Peterson (2011) found that...
(Lillard & Peterson, 2011)
Three or more authors:
Galvao and colleagues (2014) found that...
Galvao et al. (2014) found that...
(Galvao et al., 2014)
How to cite multiple studies at once
If you say that prior studies (plural) support a position or have tested an association, you should cite at least two sources. When citing two or more references, be sure to list them in alphabetical order according to the first author's last name. In between each reference (after the year), put a semicolon. Do not add "and" or "&" between references (only use a semicolon).
Support from an adolescent's peers is protective against the detrimental effects of parent-child conflict (Rogers & Rose, 2002; Sentse et al., 2010).
Alternatively, you can cite a review article. Below are examples of how you might cite one, highlighting that it is a review paper.
Several studies have suggested the early pubertal development in girls is associated with increased risk for depression (for review, see Galvao et al., 2014).
A recent review by Galvao and colleagues (2014) examined associations between early pubertal development and risk for depression in girls.
Do not include first or middle initials in the in-text citations. Those only go in the reference list. Occasionally, researchers will use the authors first and last name when writing the reference in the sentence (e.g. "Jean Piaget (1928) theorized that..."), but it's relatively uncommon.
The one exception to this is if you have works by different authors who have the same last name (e.g. references from Douglas A. Granger and from Robert C. Granger), in which case you would cite them as (D. A. Granger & Johnson, 2005) or (R. C. Granger, 2002).
When citing at the end of a sentence, the period should always go outside of the parentheses.
When citing in parentheses, use "&" instead of writing out "and".
APA format uses the Oxford comma. This means you should include a comma before the "&" when citing a paper by three to five authors.
When citing more than two authors, do not put a comma after the first author's last name. Also, et al. is all lowercase and only has a period after "al" (et al. is a Latin abbreviation for et alia). Put a comma after "al." so that it looks like "Galvao et al., 2014".
Page numbers are only included when you are using a direct quotation from the source. I'm not including instructions on how to do a direct quotation because you shouldn't plan on using them (and if you're writing a paper for one of my classes, you will lose a lot of points if you include a direct quotation). Take a few extra minutes to put it into your own words!
If you have more than one reference that has the same in-text citation (e.g. two papers published by Mittal and Walker in 2011), use a lowercase letter after the year to differentiate them: (Mittal & Walker, 2011a) and (Mittal & Walker, 2011b). These letters should also appear in the reference list citation (see Reference list page for instructions).