For field survey four important studies of infectious disease are to be made (1) Sample infection rate in different seasons and different months of a year (2) Pest and host population ratio (3) infection rate: mortality rate (4) Ration of diseased and un- diseased population (5) Clinical mortality versus real field mortality (6) Immune tolerance and prophylactic measures taken.

Could you give more information for your study? What disease? Over one site or many? Are you looking to test for an effect of time on prevalence? Is time measured continuously or discretely? These are important aspects to know before recommending an analysis.

You can use # cases per 100,000 mid-year population for the respective months. Construct confidence interval around the prevalence rates for the different months and this will guide as to whether there is differences in the rates.

Hello! If you have now access to data collected under 4 years it could be good to start doing an epidemic channel. Does it happens the same pattern every year? Is it related to rain season or to different particular days (like independence day, Christmas, etc.). If it has the same monthly pattern you can use the mean of the four year to have more power in the data when you do the scientific analysis. Which geografical area covers the data? covers both mountain areas as well as low lands areas? if it is so, it is better to do different epidemic channels. Depending of the prevalence of the study problem do as the other recommend: use rates to compare months and to compare geografical areas.

You can do if you have multiple measurements over time of trannsversal type; you might perform an analysis of time series. This allows to analyze trends over time taking into account the effect of chance in the results

Hello Sadia, what statistical tests you use will depend on what you are trying to determine and what statistical expertise you have access to. I would suggest you read up on seasonal variation and time series analysis as this is an extensive area of methodological research in epidemiology eg see

http://books.google.com.au/books?hl=en&lr=&id=qKzyAbdaDFAC&oi=fnd&pg=PP1&dq=seasonal+variation+time+series+analysis&ots=sxv263TzSr&sig=W0CzlcKb1IzgXlQa3O1CUoBWRjo#v=onepage&q=seasonal%20variation%20time%20series%20analysis&f=false

http://www.ouw.co.uk/Time-Series-Open-University-Course/dp/0749213671?field_availability=-1&field_browse=1402045031&field_keywords=Time+series&id=Time+Series+Open+University+Course&ie=UTF8&refinementHistory=generic_text_1-bin%2Cgeneric_text_2-bin%2Csubjectbin&searchKeywords=Time+series&searchNodeID=1402045031&searchPage=1&searchRank=salesrank&searchSize=12

Hello Sadia,

  you can use one of  morbidity measures, namely, person-time. Person-time is used when at-risk people are not observed throughout the whole time period. For person-time, calculate an incidence rate (incidence density) with a denominator that includes the time the person was at-risk and observed, eg.

◦ Person-months

◦ Person-years

   Please kindly remeber that prevalence is the number of people who are affected by a disease/condition at a specific time over the number of people in the population at that time.

  I would like also recommed you to look at both, point prevalecne and period prevalence and check what option will meet your expectations the most.

Good Luck!!!

Dear Sadia,

If you want to measure the statistical differences in all months of the year, can use ANOVA, to explore the differences between the months and if there are any statistical differences and then conclude your study.

The question certainly needs clarification!