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5 Practical Matters: Beginning a Meta-Analytic Database

5 Practical Matters: Beginning a Meta-Analytic Database

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56



PLANNING AND PREPARING A META-ANALYTIC REVIEW



meta-­analysis. I suggest that you be rather inclusive during this initial screening, retaining any studies that might meet your inclusion criterion. You should

also retain any nonempirical works, such as reviews or theoretical papers;

although these do not provide empirical results for your meta-­analysis, it will

be worthwhile to read them (1) to identify additional studies cited in these

papers, and (2) to inform interpretation of results of your meta-­analysis.

As you are identifying works that you will retain, it is critical to have some

way of organizing this information. I use spreadsheets such as that shown in

Table 3.1. (I have shown only four studies here, your spreadsheet will likely

be much larger.) Although you should develop an approach that meets your

own needs, this example spreadsheet contains several pieces of information

that I recommend recording. The first column contains a number for each

paper (article, chapter, dissertation, etc.) identified in the search. The number is arbitrary, but it is useful for filing purposes (as the number of papers

becomes large, it is useful to file them by number rather than, e.g., author

name). The next four columns contain citation information for the paper. This

information is useful not only for citing the paper in your write-up, but in

identifying repetitive papers during your multiple search strategies (for this

purpose, having this information in a searchable spreadsheet is useful). The

sixth column contains the abstract, which is useful if you want to search for

specific terms within your spreadsheet. I recommend copying this information into your spreadsheet if it is electronically available, but it probably is not

worth the time needed to type this in manually. The seventh column identifies where and when the paper was found; recording the date is important

because (1) you might want to update the search near the completion of your

meta-­analysis, and (2) you should report the last search dates in your presentation of your meta-­analysis. The two rightmost columns (columns eight and

nine) contain information for retrieving and coding the reports. One column

indicates whether you have the report, or the status of your attempt to retrieve

it (e.g., the third paper notes that I had requested this dissertation through my

university’s interlibrary loan system). The last column will become relevant

when you begin coding the studies (see Chapters 4–8). Here, I have recorded

the person (BS = Brian Stucky, the second author on this paper) who coded

this report and the date it was coded. Recording both pieces of information

are valuable in case you later identify a problem in the coding (e.g., if one

coder was making a consistent error) or if you revise the coding protocol (you

then need to modify the coding of all studies coded before this change). In

this column, I also record when studies are excluded for a particular reason;

for instance, the fourth study was excluded because it used an adult sample

(which was one of the specified exclusion criteria in this review).







57



Hawley, Little,

and Card



Blachman



Bailey and

Ostrov



2



3



4



In press



2003



2007



1995



Year



Differentiating

forms . . .



Predictors of

peer . . .



The allure of a

mean friend . . .



Relational

aggression . . .



Title



Journal of Youth and Adolescence



Dissertation, University of

California, Berkeley



International Journal of

Behavioral Development, 31(2),

170–180



Child Development, 66(3),

710–722



Source



The

purpose . . .



Examined

the role . . .



Recent

theory . . .



Assessed a

form . . .



Abstract



E-mail request



Proquest

dissertation



PsycINFO

(May 2007)



PsycINFO

(Nov. 2005)



Found in



Yes



Requested

ILL



Yes



Yes



Have



Adults



NC, 9/12/07



BS, 12/1/05



Entered



Note. The table lists Bailey and Ostrov as “in press” even though it was published in 2008. I left the date in the table as “in press,” however, because the table is meant to

show progress as it occurred during the time of this research (which was prior to this work being published).



Crick and

Grotpeter



Authors



1



Paper

No.



TABLE 3.1. Example Spreadsheet for Organizing a Literature Search



58



PLANNING AND PREPARING A META-ANALYTIC REVIEW



Of course, you may use a different way of organizing information from

your literature search. The point is that you should have some way of organizing information that clearly records important information and avoids any

duplication of effort.



3.6 Summary

One of the most important steps of a meta-­analytic review is obtaining the

sample of studies that will provide the data for your analyses. To define this

sample, we need to specify a clear set of inclusion and exclusion criteria

specifying what types of studies will and will not comprise this sample. We

then search the literature for studies fitting these inclusion criteria. Several

approaches to searching for literature exist, and I have described some of

the more common methods. The goal of this search is to obtain an unbiased,

typically exhaustive (i.e., complete) sample of studies.



3.7Recommended Readings

Reed, J. G., & Baxter, P. M. (2009). Using reference databases. In H. Cooper, L. V. Hedges,

& J. C. Valentine (Eds.), The handbook of research synthesis and meta-­analysis (2nd

ed., pp. 73–101). New York: Russell Sage Foundation.—This chapter provides a very

detailed, practical guide to using electronic databases, including forward search databases.

Hopewell, S., Clarke, M., & Mallett, S. (2005). Grey literature and systematic reviews. In H.

R. Rothstein, A. J. Sutton, & M. Borenstein (Eds.), Publication bias in meta-­analysis: Prevention, assessment and adjustments (pp. 49–72). Hoboken, NJ: Wiley.—This chapter

describes several ways of identifying and retrieving studies that are more obscure

than traditional journal articles, and discusses the biases potentially introduced by not

including this literature.



Notes

  1. The details (e.g., effect sizes, distributions around the mean) of this example will

become clearer as you read subsequent chapters. For now, you should just try to

understand the gist of this example.

  2. In principle, a meta-­analysis does not need to include all studies that exist.

Instead, you can select a random sample of all existing studies on which to perform your analyses, assuming the studies you have selected provide adequate







Searching the Literature



59



statistical power to evaluate your research questions. I view this type of random

sampling as an extremely valuable approach to performing reviews in areas where

there is so much empirical literature that a full meta-­analysis is not practical.

However, very few meta-­analytic reviews use this random-­sampling approach;

nearly all attempt to be exhaustive in their inclusion of studies. Unfortunately,

this typical practice of being exhaustive seems to have created a standard where

meta-­analytic reviews are expected to be exhaustive, and the random-­sampling

approach would likely draw criticism.

  3. The importance of developing clear operational definitions of constructs is

important regardless of effect sizes used, whether they are of single variables

(e.g., means or proportions) or multivariate effect sizes (see Chapter 7).

  4. If you are particularly interested in drawing cross-­cultural conclusions and there

exists adequate numbers of studies written in a tractable number of languages,

it may be possible to hire translators. However, you should remember that coding studies is an intensive effort (see Chapters 4 and 5) that requires considerable technical expertise. Because it would be difficult to find someone with both

multilingual and meta-­analytic skills, and require considerable amounts of their

time, this is not a viable alternative in the vast majority of cases. For this reason,

restriction of populations of studies to those written in languages you know is

often reasonable as long as you recognize this restriction.

  5. This condition is necessary to include a study in your analyses. However, you

should also consider whether the studies that report insufficient information differ in meaningful ways, with the most relevant possibility being that the results

were nonsignificant. If you find that a considerable number of studies report

insufficient information to compute effect sizes (and other efforts, such as contacting the authors, do not alleviate this problem), then you should report these

studies in your report for transparency.

  6. Here, performing the meta-­analysis with a random sample of studies might be

preferable to changing your inclusion/exclusion criteria, especially if doing so

makes the population of studies of lesser interest. Footnote 2 of this chapter

describes some of the challenges to this approach.

  7. To illustrate this cost, consider my experience when publishing the example

meta-­analysis I use throughout this book: During this review process, one of the

reviewers suggested that I “plow through” the approximately 30,000 studies that

could be identified using a very general search term like “aggression.” Assuming

10 minutes to review each study for possible inclusion (which is a conservative estimate), this process would have taken over two years of 40 hours/week

reviewing. During this time, approximately 3,000 additional studies identified

using this search term would have been added, thus requiring another 3 to 4

months of full-time reviewing. Furthermore, during the coding, analysis, and

write-up of these results, a couple thousand more works would likely have been



60



PLANNING AND PREPARING A META-ANALYTIC REVIEW

added to the database. Although this reviewer was certainly trying to be helpful

by ensuring high recall, this example illustrates that the cost of low precision

can be substantial in making a meta-­analysis impossible.



  8. The use of nonacademic search engines (e.g., Google scholar) might be especially

plagued by inconsistency in what works are included. I personally do not use

these nonacademic search engines. If you do decide to use one, I recommend

not using it as a primary search method, but rather as a check of the adequacy

of your other search procedures (i.e., after searching for literature using other

methods, does this nonacademic search engine uncover additional works that

should have been included?).

  9. We did not do so in the actual meta-­analysis because the number of studies using

samples outside of this age range was reasonably small.

10. To my knowledge, no one has evaluated this possibility empirically. I also suspect that factors unrelated to the effect sizes (e.g., length of time since the presentation, your persuasiveness and persistence in requesting presentations) are

more influential with regard to response than the effect sizes. But this possibility

of biased response should be kept in mind when response rates are low, and it

might be worthwhile to evaluate this possibility (through, e.g., funnel plots or

effect size–­sample size correlations; see Chapter 11) among the conference presentation included in your meta-­analysis.

11. I do not believe that anyone has evaluated this empirically.

12. I find it comforting to consider that, just as there has never been a flawless study

(see quote by Cooper, 2003, in Chapter 2 of the present volume), there has never

been—and never will be—a flawless meta-­analysis. Although you might strive

to obtain every study within your sample, there comes a point of diminishing

returns where a tremendous amount of additional effort yields very few additional benefits. When this point is reached, your field benefits more from timely

completion and dissemination of your meta-­analysis than futile efforts to obtain

additional studies.

13. This image might seem quaint to some readers. If you prefer, point-and-click

your way through the online tables of contents of some relevant journals.



Part II



The Building Blocks

Coding Individual Studies



4



Coding Study Characteristics



Performing the simplest meta-­analysis, in which the goal is simply to estimate

a typical (mean) effect size and perhaps to make statistical inferences about

this effect size (see Chapters 8 and 10), requires only that you code the effect

sizes and sample sizes (to compute the standard errors of the effect sizes) from

each study (see Chapter 5). If you wish to correct for artifacts to these effect

sizes, it is also necessary to code information for these corrections such as the

reliabilities and dichotomizations of variables comprising the effect sizes (see

Chapter 6).

Performing this sort of simple meta-­analysis may seem adequate if it

answers all of your research questions. However, this approach would fail to

provide information about why effect sizes might differ across studies, a question that might be a key motivator of the meta-­analysis (see Chapter 2) or a

valuable follow-up to observed heterogeneity (Chapter 8). Moderator analyses attempt to explain this heterogeneity among effect sizes by evaluating

whether coded study characteristics systematically predict variation in effect

sizes across studies (see Chapter 9). To perform these moderator analyses, it

is necessary that you code relevant study characteristics that might be useful in

predicting variation in effect sizes across studies.

In addition to coding study characteristics for moderator analyses, thorough coding of these characteristics is important simply for describing the

research basis for your meta-­analysis. In other words, what does the sample

of studies from which you draw your conclusions look like? This description is

useful both in describing the population to which you can make conclusions

(see Chapter 3 for a discussion of conceptualizing samples and populations

of studies) and in identifying gaps within the research. For example, does your

meta-­analysis rely primarily on studies using a particular measure or type of





63



64



CODING INDIVIDUAL STUDIES



measure to the exclusion of others, or certain types of samples to the neglect

of others? Answers to these questions inform both the extent to which you can

generalize your conclusions and where it might be valuable to perform future

primary research.

In short, almost every meta-­analysis will benefit from careful coding of

study characteristics, whether you use them for performing moderator analyses

or for describing the sample of studies. In this chapter, I first describe considerations in selecting study characteristics to code (Section 4.1) and then turn

to the specific topic of coding study quality (Section 4.2). I next describe the

important step of evaluating coding decisions (Section 4.3). Finally, I provide

practical suggestions for developing a coding protocol to guide the coding of

studies (Section 4.4).



4.1 Identifying Interesting Moderators

Decisions about which study characteristics to code need to be heavily

informed by your knowledge of the content area in which you are performing

a meta-­analytic review. Nevertheless, I describe two sets of general considerations that I believe apply to meta-­analytic reviews across fields: considering

the research questions you are interested in and considering coding certain

specific aspects of studies.

4.1.1Considering Research Questions of Interest

Just as planning a primary research study requires you to select variables

based on your research questions, planning a meta-­analysis requires that you

base your decisions about which study characteristics to code on the research

questions that you wish to answer. If your research questions are exclusively

about average effect sizes across studies (i.e., combining studies), then you

might not need to code much beyond effect sizes, sample sizes, and information for any artifact corrections you wish to make. I qualify this statement

by noting that it is still valuable to be able to provide basic descriptive information about this sample of studies to inform the generalizability of your

review. Nevertheless, the number of study characteristics that you will need

to code to address this research question adequately is small.

In contrast, if at least some of your research questions involve comparing studies (i.e., identifying whether studies with certain features yield

larger effect sizes than studies with other features), then it will be much more

important to code many study characteristics. Obviously, if you put forth







Coding Study Characteristics



65



a research question about a specific characteristic moderating effect sizes

(e.g., do studies with this characteristic yield larger effect sizes than studies

without this characteristic?), then it will be necessary to code this specific

characteristic. However, you should also consider what study characteristics

might commonly co-occur with the characteristic you are interested in, and

code these. For example, if you are interested in investigating whether studies with certain types of samples yield different effect sizes (e.g., children vs.

adults), you should carefully consider the other study characteristics that

are likely to differ across these types of samples (e.g., studies of adults might

frequently rely on self-­reports, whereas studies of children might frequently

rely on parent reports, observations, etc.). If you fail to code these other study

characteristics, then you cannot empirically rule out the possibility that your

results involving the coded study characteristic of interest are not really due

to these co-­occurring characteristics. In contrast, if you do code these characteristics, then you are able to evaluate empirically such competing explanations (see Chapter 9).

As a more extreme version of research questions involving specific moderators, some meta-­analysts aim to predict all heterogeneity in effect sizes by

coded study characteristics. Although this goal tends to be quite exploratory,

and you would therefore view the findings of moderation by specific characteristics cautiously, it nevertheless is a goal you might consider. If so, then

you will necessarily code a large number of study characteristics; specifically,

you will code any study characteristics that meet two conditions. First, the

study characteristics are consistently reported in many or even most studies;

this is necessary to avoid a preponderance of missing data when you evaluate the coded characteristic as a moderator. The second condition is that the

study characteristic varies across at least some studies; this variability across

studies is necessary for the study characteristic to covary with effect sizes.

You would then enter these coded study characteristics into some large predictive model (e.g., forward stepwise regression) to explore relations between

them and variation in effect sizes.

4.1.2Considering Specific Aspects of Studies

As I mentioned, the exact study characteristics you code will depend on your

research questions and be informed by your knowledge of the topic area.

Nevertheless, four general types of characteristics should be considered in

any meta-­analysis in the social sciences: characteristics of the sample, measurement, design, and source (see also Lipsey, 2009; Lipsey & Wilson, 2001,

pp. 83–86). These are summarized in Table 4.1.



66



CODING INDIVIDUAL STUDIES



TABLE 4.1.  Summary of Study Characteristics to Consider Coding

Broad aspect



Narrow aspects



Examples



Sample

characteristics



Sampling procedures



Sampling from unique settings,

representative sample, country



Demographic features



Gender composition, ethnic composition,

socioeconomic status, age, IQ



Sources of information



Self-­report, other reporter (e.g., spouse,

parent, teacher), observations



Measurement process



Covert versus overt observations, timed

versus untimed performance



Specific measures used



Specific measure, original versus short

forms, translations



Type of design



Experimental, quasi-­experimental, pre–

post comparisons, regression discontinuity



Specific design features



Type of control group, length of

longitudinal time span



Publication status



Published versus unpublished, publication

quality



Year of study



Year of publication, year of data collection



Funding



Funded versus unfunded, source of

funding



Researcher characteristics



Discipline, gender, ethnicity



Internal validity



Use of random assignment, condition

concealment, attrition



External validity



Use of random sampling procedures,

samples based on specific subpopulations



Construct validity



Reliability of measures (for correction

rather than exclusion or moderator

analyses), relevant measurement

characteristics (described above)



Measurement

characteristics



Design

characteristics



Source

characteristics



Study quality



4.1.2.a Sample Characteristics

Potentially relevant characteristics of the sample that you might consider

include aspects of the sampling procedure and the demographic features

of the sample. For instance, you might code sampling procedures such as

whether the sample was drawn from unique settings (e.g., from a university setting, some sort of clinical setting, a correctional facility, or specific

other settings relevant to the area), whether the study attempted to draw a



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