Behavioural Surveillance Surveys - The Wisdom of Whores

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EXAMPLE : CALCULATING THE CHI-SQUARE STATISTIC BY HAND The following illustrates a step-by-step process of calculating the chi-square statistic : Set up the explanatory variable in columns, and the outcome variable in rows. Then calculate the row and the column totals. Next, calculate the expected number of observations for each cell if there were no difference in distribution according to the explanatory variable (i.e., if the null hypothesis were true). Do this as follows : Table of observed numbers The expected number = row total * column total overall total N Chi-square is calculated by comparing the numbers actually observed with those expected if there were no difference in distribution according to the explanatory variable. For every cell of the table, calculate the difference between the expected and observed values (and square it to get rid of any negatives) and then divide it by the expected value. Now add together the result of that calculation for every cell of the table. The result is the chi-square value. In other words χ 2 = SUM (observed - expected) 2 expected Once the χ 2 value has been calculated, it can be compared with the Chi-square Table to determine whether there is indeed a statistically significant association between the explanatory and the outcome variables. Notice that the table uses the term degrees of freedom. The statistical significance of χ 2 depends on how many categories there are in both the explanatory and the outcome variables. The degrees of freedom (DF) can be calculated easily by looking at the table laying out the variables, as follows : DF = (number of rows - 1) * (number of columns - 1) The steps below refer to the example provided in Chapter 7 of the analysis of the number of non-regular sex partners by age group. Step 1 : Set up the explanatory variable in columns, and the outcome variable in rows. Then calculate the row and the column totals. 0 1 2 3+ Totals < 20 years 12 4 6 9 31 20 - 24 87 36 21 27 171 25 - 29 75 29 11 18 133 30+ 177 26 11 13 227 Totals 351 95 49 67 562 348 A PPEN DI X 5 B EHAV I OR A L SURV EI L L A NC E S U R V EY S
Step 2 : Calculate the expected number of observations for each cell if there were no difference in distribution according to the explanatory variable (i.e., if the null hypothesis were true). Do this as follows: Table of expected numbers The expected number = row total * column total overall total N For cell one (
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BEHAVIORAL SURVEILLANCE SURVEYS GUI
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Family Health International (FHI) H
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Chapter 7 Analysis and interpretati
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3. Choosing populations for behavio
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G UIDELINES FOR REPEATED BEHAVIORAL
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Recognizing that HIV surveillance d
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Different approaches to collecting
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The principal rationale for focusin
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It is not possible to validate data
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GUIDELINES FOR REPEATED BEHAVIORAL
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The process of building partnership
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Funders of HIV prevention activitie
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What is to be measured ? Indicators
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Step 7 : Constructing a sampling fr
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Step 12 : Data collection and super
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choosing population groups GUIDELIN
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the spread of HIV. For this reason,
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In some circumstances, public healt
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The majority of sub-populations of
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In the end, the issue boils down to
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In looking at behaviors of hard-to-
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Maps derived from program planning
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Selecting primary sampling units (c
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...when measures of size are not av
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If there is no reason to believe th
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Figure 3 : Decision tree for first-
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Implications of alternative samplin
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Table 5 : Values of Z 1-α and Z 1-
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Table 6 : Sample size requirements
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equired. In this case, the pros and
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Should one- or two-tailed z-score v
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Other measurement issues for BSS Th
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A “low-tech” solution to the pr
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5 Weighting in multi-stage sampling
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Figure 6 : Procedures for calculati
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Calculating weights from sampling p
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Calculating standard errors with mu
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6 Adapting and using questionnaires
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Some attempts have in the past been
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Informed consent Confidentiality an
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Recommended Methods of Statistical
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where n is the sample size in the d
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Table 2 : Reported number of non-re
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False conclusions: the danger of co
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Analysis of trends in behavior over
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Changes in sampling methodology ove
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8 Using the data collected to impro
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Improving prevention programs As a
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Finally, information about HIV and
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Figure 9 : HIV and STD prevalence,
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9 Indicators This guide identifies
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The standard questionnaires are acc
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INDICATORS Page INDICATORS FOR YOUT
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INDICATORS Page INDICATORS FOR MEN
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KEY INDICATORS What follows is a fu
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The indicator uses promoted data. O
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To be counted the numerator for thi
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Strengths and limitations Some meas
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Adult Indicator 5 Consistent condom
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Adult Indicator 7 (men only) Number
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Adult Indicator 9 Consistent condom
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Adult Indicator 11 Population seeki
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Adult Indicator 12 Exposure to inte
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Youth Indicator 2 No incorrect beli
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Youth Indicator 4 Youth sexually ac
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Youth Indicator 6 Number of sexual
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Youth Indicator 8 Consistent condom
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Youth Indicator 10 Commercial sex a
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Youth Indicator 14 Exposure to inte
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Female Sex Worker Indicator 2 No in
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Female Sex Worker Indicator 5 Sex w
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Indicators for men who have sex wit
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Men Who Have Sex With Men Indicator
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Men who have sex with men Indicator
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Indicators for injecting drug users
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Injecting Drug User Indicator 3 Inj
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Injecting Drug User Indicator 8 Dru
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Injecting Drug User Indicator 10 Dr
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Suggested Reading Brown T, Sittitra
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QUESTIONNAIRE For Adult Target Grou
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The ADULT questionnaire includes th
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FHI 1999 HIV/AIDS/STD BEHAVIORAL SU
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POSSIBLE ADDITIONAL QUESTIONS Commu
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STD Treatment seeking behaviors No.
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STD Treatment seeking behaviors (co
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QUESTIONNAIRE For Unmarried Male An
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The YOUTH questionnaire includes th
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No. Questions and filters Coding ca
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Stigma and Discrimination No. Quest
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FAMILY HEALTH INTERNATIONAL (FHI) H
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STD Treatment seeking behaviors No.
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STD Treatment seeking behaviors (co
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QUESTIONNAIRE For Men Who Have Sex
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The MSM questionnaire includes the
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STD Treatment seeking behaviours No
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No. Questions and filters Coding ca
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QUESTIONNAIRE For Injecting Drug Us
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This questionnaire includes the fol
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EXAMPLE OF SUPERVISORS’ AND INTER
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A “take-all” approach is to be
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• To probe for additional informa
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Part B: How to use the Long Distanc
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An example of a question for which
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Part C: Section-by-section review o
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Q109. If the respondent says he/she
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it is asking if the respondent has
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Page 351 and 352: Form 3 Assignment Information Sheet
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Page 355: TABLE OF CHI-SQUARE STATISTICS AND
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Behavioural Surveillance Surveys - The Wisdom of Whores

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